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2D Bi2O2Se with high mobility for high performance polymer solar cells
Abstract
Carrier mobility of the active layer plays a critical role in the photovoltaic performance of polymer solar cells (PSCs), and the low charge carrier mobility still limits performance improvement of PSCs. Adding high mobility materials to the active layer is an effective way to improve the performance of PSCs. Two-dimensional (2D) Bi2O2Se can be an ideal additive material for improving the carrier mobility of active layer due to its ultrahigh mobility and excellent thermal stability. In this work, we fabricate successfully the Bi2O2Se few-layer 2D nanoflakes by combining lithium intercalation with shear force-assisted liquid phase exfoliation and apply it as a third component to improve charge carrier mobility in PSCs for the first time. The 2D Bi2O2Se nanoflakes, when introduced into the active layer, not only provide an additional low energetic loss donor/acceptor (D/A) interfaces and efficient charge transfer pathways but also induce crystallization of PBDB-T and ITIC and form the continuous interpenetrating networks, which promotes the exciton dissociation, charge transfer and collection process in the PSCs. As result, the PCE based on PBDB-T:ITIC device is increased from 10.09% for binary device to 12.22% for optimized ternary device (2 wt%). Meanwhile, the PCE based on PM6:Y6 device is also increased from 14.59% for binary device to 16.28% for optimized ternary device (2 wt%). Moreover, the optimized ternary device shows excellent air stability by retarding the phase mixing in the active layer during the aging period. This work provides an effective way to improve the performance of PSCs, also shows the Bi2O2Se material has potential application in solar cells.
... 27 Since then, a large number of studies have followed the work and reported the successful fabrication of various Bi 2 O 2 Se based nanostructures, such as 1D nanowire, 49,50 nanoribbon 51 and 0D quantum dots. 52 A variety of applications have been demonstrated, such as photodetector, 28,[53][54][55] transistor, 27,51,[56][57][58][59][60][61][62][63] optical switch, 64,65 terminal memristor, 66 solar cells, 67 Josephson junction, 68 digital devices, [49][50][51] and so on. Furthermore, Bi 2 O 2 Se also showed promising potential in the post-silicon era. ...
... So far, Bi 2 O 2 Se crystals have been prepared by various methods. For bulk Bi 2 O 2 Se, the preparation methods include solid state reaction, 30,43,[93][94][95][96] gas-phase transport reaction, 57 spark plasma sintering (SPS) process, 31,42,43,47,97 chemical vapor transport (CVT) method, 52 Zhang's method, 67 oxygenation method, 98 and modified Bridgman method. 65,99,100 For 2D Bi 2 O 2 Se thin film, the major methods are composite-molten-salt (CMS) method, 48 chemical vapor deposition (CVD), [27][28][29]53,[56][57][58][59]81,[101][102][103] low-pressure CVD, 54,104-106 hydrothermal reaction (HTR), 64 chemical vapor transport (CVT) method, 107,108 molecular beam epitaxy (MBE), 109 pulsed laser deposition (PLD), 110 vapor-solid (VS) deposition approach, 62 shear exfoliation, 111,112 wet chemical procedure, 113 solution-assisted method, 63 liquid-phase mechanical exfoliation, 67,114 and one-step hydrothermal method. ...
... For bulk Bi 2 O 2 Se, the preparation methods include solid state reaction, 30,43,[93][94][95][96] gas-phase transport reaction, 57 spark plasma sintering (SPS) process, 31,42,43,47,97 chemical vapor transport (CVT) method, 52 Zhang's method, 67 oxygenation method, 98 and modified Bridgman method. 65,99,100 For 2D Bi 2 O 2 Se thin film, the major methods are composite-molten-salt (CMS) method, 48 chemical vapor deposition (CVD), [27][28][29]53,[56][57][58][59]81,[101][102][103] low-pressure CVD, 54,104-106 hydrothermal reaction (HTR), 64 chemical vapor transport (CVT) method, 107,108 molecular beam epitaxy (MBE), 109 pulsed laser deposition (PLD), 110 vapor-solid (VS) deposition approach, 62 shear exfoliation, 111,112 wet chemical procedure, 113 solution-assisted method, 63 liquid-phase mechanical exfoliation, 67,114 and one-step hydrothermal method. 115 For 1D Bi 2 O 2 Se, space-confined CVD method 49 and gold-catalyzed vapor-liquid-solid (VLS) method 50 are employed to synthesize nanowires; Solution-based method is used to prepare quantum dots, 52 and bismuth-catalyzed VLS approach is used to synthesize nanoribbons. ...
Layered two‐dimensional (2D) materials have garnered marvelous attention in diverse fields, including sensors, capacitors, nanocomposites and transistors, owing to their distinctive structural morphologies and superior physicochemical properties. Recently, layered quasi‐2D materials, especially layered bismuth oxyselenide (Bi2O2Se), are of particular interest, because of their different interlayer interactions from other layered 2D materials. On this basis, this material offers richer and more intriguing physics, including high electron mobility, sizeable bandgap, and remarkable thermal and chemical durability, rendering it an utterly prospective contender for use in advanced electronic and optoelectronic applications. Herein, this article reviews the recent advances related with Bi2O2Se. Initially, its structural characterization, band structure, and basic properties are briefly introduced. Further, the synthetic strategies for the preparation of Bi2O2Se are presented. Furthermore, the diverse applications of Bi2O2Se in the field of electronics and optoelectronics, photocatalytic, solar cells and sensing were summarized in detail. Ultimately, the challenges and future perspectives of Bi2O2Se are included. image
... In 2019, Tong et al. used Bi2O2Se nanosheets to fabricate a wideband photoelectric transistor with high photoelectric responsivity [19]. In 2020, Huang et al. prepared Bi2O2Se and used them for the first time as additives to promote the charge transfer of PSCs [20]. In 2020, Xu et al. used Bi2O2Se nanosheets to detect trace oxygen and obtained a resistive sensor, indicating that it is an ideal candidate material for trace oxygen detection [21]. ...
... Bi2O2Se material has ultra-high carrier mobility at room temperature, and the absorbed energy can be directly used to promote electronic transfer, which can efficiently enhance the absorbance of light energy and enable the optocarriers to drift out of the metal-Bi2O2Se interface more rapidly and excite more intense SPR phenomena. Also, compared to precious metal nanoparticles such as gold and silver, the much larger specific surface area of Bi2O2Se provides more interfaces for exciton separation and charge transfer, and better contact with the detected material [20,32] 335 1.340 1.345 1.350 1.355 1.360 1.365 1 ...
In this work, we firstly used a new two-dimensional (2D) semiconductor material Bi2O2Se for optical-fiber SPR sensor sensitization, proposed and validated a U-shaped optical-fiber SPR sensor with Au film- Bi2O2Se Sandwich structure. The finite element simulation results illustrate that the electric field strength on the surface is 2.08 times higher than that of the pure Au film, which excites a stronger SPR phenomenon thus leading to a high sensitivity of the sensor. The effect of the Radius on the sensor performance was investigated, and the optimal structural parameters were derived to fabricate the sensing probes. The RI sensitivity of the presented sensor is 6827.41 nm/RIU, 1.98 times superior to that of the pure Au film U-shaped optical SPR sensor. The sensor is insensitive to temperature fluctuations and has good repetitive and environmental stability. The proposed sensor has good potential for future applications in biomass detection, which also indicates that Bi2O2Se has good prospects for future applications in optoelectronic devices.
... 4(e) and 4(f)]. 86 A statistical analysis of transmission electron microscopy (TEM) results indicates that the average lateral dimension size and thickness of as prepared 2D Bi 2 O 2 Se are 47 and 2.8 nm, respectively. ...
... ). Copyright 2020 American Chemical Society.86 (g) Schematic diagram of tape exfoliation. ...
Two-dimensional (2D) materials have drawn much attention in recent years ascribing to their unique properties associated with atomic thickness. Besides graphene, which has aroused tremendous research interest, other 2D materials such as [Bi2O2]-based layered compounds, i.e., Bi2O2Se, BiOCl, and Bi2Sr2CaCu2Ox, have also been studied widely and show promising application prospects in electronics, optoelectronics, photocatalysis fields, and so on. In this Perspective, we systematically review the progress on preparation methods of 2D [Bi2O2]-based layered materials, discuss the strengths and drawbacks of different methods, and give an outlook toward future research directions.
... Hydrothermal synthesis is a simple and effective method for mass preparation of 2D materials, [82][83][84] which has been widely used to synthesize 2D Bi 2 O 2 X flakes 85 reported the synthesis of Bi 2 O 2 S nanosheets by using Bi(NO 3 ) 3 Á5H 2 O and SC(NH 2 ) 2 as precursors in concentrated alkaline (KOH and NaOH) aqueous solution. Bi(NO 3 ) 3 hydrolyzes into BiONO 3 in alkaline solution, and then the as-produced BiONO 3 reacts with SC(NH 2 ) 2 to form Bi 2 O 2 S. The chemical reactions involved in this process are as follows: Figure 5(B)) and the thickness of most flakes is~2 nm ( Figure 5(C)). ...
... Currently, many (Table 2). 76,83,85,86,97,[126][127][128][129][130][131][132][133][134][135][136][137] Yan and coworkers fabricated near-infrared photodetectors based on 2D Bi 2 O 2 S flakes prepared by hydrothermal synthesis (Figure 11(A)). 85 The photodetector exhibited pronounced photoresponse under 785 nm light illumination with various power densities from 0.05 to 500 mW cm À2 (Figure 11(B)). ...
Atomically thin two‐dimensional (2D) bismuth oxychalcogenides (Bi2O2X, X = S, Se, Te) have recently attracted extensive attention in the material research community due to their unique structure, outstanding long‐term ambient stability, and high carrier mobility, which enable them as promising candidates for high‐performance electronic and optoelectronic applications. Herein, we present a comprehensive review on the recent advances of 2D bismuth oxychalcogenides research. We start with an introduction of their fundamental properties including crystal structure and electronic band structure. Next, we summarize the common techniques for synthesizing these 2D structures with high crystallinity and large lateral size. Furthermore, we elaborate on their device applications including transistors, artificial synapses, optical switch and photodetectors. The last but not the least, we summarize the existing challenges and prospects for this emerging 2D bismuth oxychalcogenides field.
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... For instance, directional sintering technology can be employed to form texture along the [001] crystallographic direction [32], thereby reducing the κ ph of BOSC and BOSB. Refining nanosheets through shear exfoliation [39] or mixing highly conductive materials like graphite nanosheets [40] are feasible scenarios for enhancing the electrical conductance of layered materials. The density of states near the Fermi level can be increased through doping BOSC and BOSB at Bi or O sites, based on resonant level theory [19], which can help optimize S. ...
The multiple anion superlattice Bi4O4SeCl2 has been reported to exhibit extremely low thermal conductivity along the stacking c-axis, making it a promising material for thermoelectric applications. In this study, we investigate the thermoelectric properties of Bi4O4SeX2 (X = Cl, Br) polycrystalline ceramics with different electron concentrations by adjusting the stoichiometry. Despite optimizing the electric transport, the thermal conductivity remained ultra-low and approached the Ioffe–Regel limit at high temperatures. Notably, our findings demonstrate that non-stoichiometric tuning is a promising approach for enhancing the thermoelectric performance of Bi4O4SeX2 by refining its electric transport, resulting in a figure of merit of up to 0.16 at 770 K.
... In recent years, with the fast development of polymer transfer technology, several Bi 2 O 2 Se nanosheets with high quality can be entirely isolated from mica to overcome the interfacial electrostatic force to construct 2D/2D, 2D/three-dimensional (3D) vdWs heterojunctions or other structures, leading to the improved properties and the exploration of novel functional devices such as memristors, THz-detection, phototransistors, resistance switching, photonic integrated circuits, and thermoelectrics. 15 a small dark current of 72.9 nA, a high R of 3.5 A·W −1 , a fast rise/decay time of 22/78 ns, and a low noise-equivalent power of 15.1 pW·Hz −0.5 at a V ds of 2 V for communication applications. 18 Meanwhile, in terms of Bi 2 O 2 Se/2D vdWs heterostructures, 2D materials with ambipolar conducting behavior composed of WSe 2 and BP have been integrated with Bi 2 O 2 Se to suppress the dark current, broaden the spectrum, and facilitate the response speed. ...
In recent years, two-dimensional (2D) nonlayered Bi2O2Se-based electronics and optoelectronics have drawn enormous attention owing to their high electron mobility, facile synthetic process, stability to the atmosphere, and moderate narrow band gaps. However, 2D Bi2O2Se-based photodetectors typically present large dark current, relatively slow response speed, and persistent photoconductivity effect, limiting further improvement in fast-response imaging sensors and low-consumption broadband detection. Herein, a Bi2O2Se/2H-MoTe2 van der Waals (vdWs) heterostructure obtained from the chemical vapor deposition (CVD) approach and vertical stacking is reported. The proposed type-II staggered band alignment desirable for suppression of dark current and separation of photoinduced carriers is confirmed by density functional theory (DFT) calculations, accompanied by strong interlayer coupling and efficient built-in potential at the junction. Consequently, a stable visible (405 nm) to near-infrared (1310 nm) response capability, a self-driven prominent responsivity (R) of 1.24 A·W-1, and a high specific detectivity (D*) of 3.73 × 1011 Jones under 405 nm are achieved. In particular, R, D*, fill factor, and photoelectrical conversion efficiency (PCE) can be enhanced to 4.96 A·W-1, 3.84 × 1012 Jones, 0.52, and 7.21% at Vg = -60 V through a large band offset originated from the n+-p junction. It is suggested that the present vdWs heterostructure is a promising candidate for logical integrated circuits, image sensors, and low-power consumption detection.
... 47 Therefore, Bi 2 O 2 Se has strong potential for applications in electronics, 4,21,[48][49][50][51][52] optoelectronics, 23,[53][54][55][56] detectors, 57,58 and energy technologies. 43,59,60 There are still some open questions as well as controversies and discrepancies, such as some missing Raman modes, 61,62 the origins of Rashba spin splitting, 40,63 the mechanism of the magnetic field-induced resistivity upturn, 36 T 1.5 and T 2 resistivity in the dilute limit, 33,34,36,64 magnetic field-dependent MR anisotropy, 36,37,65 quantification of spin-orbital coupling strength, 39 and the origin of quasi-ballistic transport in nanowires. 38 As an emerging novel material, our knowledge of the fundamental properties of Bi 2 O 2 Se has increasing quickly over the past 4 years. ...
With weak interlayer interactions and unique physical properties, bismuth oxyselenide (Bi2O2Se) has become a rising star as a novel quasi-2D material, possessing high symmetry, adjustable electronic structure, ultra-high electron mobility, persistent quantum oscillations, unique defects, strong spin-orbital coupling, natural oxide layers, excellent stability, and marvelous optoelectronic performance. These characteristics will help to break through existing technical barriers for applications such as field-effect transistors and photodetectors. Its unique crystal structure and suitable lattice parameters allow it to grow on lattice-matched (SrTiO3 and LaAlO3) and unmatched (mica and SiO2) substrates, establishing a link between traditional epitaxy and emerging van der Waals epitaxy. This review aims to provide an overview of this promising semiconductor from a fundamental structure, physics, and physical properties perspective. We especially pay attention to the correlation of electronic structure to various physical properties and material performance. We also identify current problems and challenges regarding the fundamental properties of this material.
... To gain more insight into the photogenerated charge recombination and extraction behavior of IPSCs, the dependences of V oc -and J sc -on light intensities (P) are investigated. The relationship between V oc and ln(P) is show as follow [66]: ...
The optimized electron transport layer (ETL) plays a crucial role in the practical application of polymer solar cells (PSCs). Herein, bio-inspired polydopamine (PDA) modified Ti3C2Tx (PDA-Ti3C2Tx) as a multifunctional additive is dispersed into ZnO to fabricate ZnO:PDA-Ti3C2Tx composite ETL. PDA-Ti3C2Tx passivates the trap states of ZnO via forming strong and stable chelate interactions through Zn²⁺ ions and PDA molecules. PDA-Ti3C2Tx also lowers the vacuum level of transport layer by forming interface dipoles between catechol of PDA and Zn²⁺ ions of zinc oxide. Moreover, PDA-Ti3C2Tx constructs additional electron transport pathways by connecting the discontinuities among ZnO nanocrystals. As such, ZnO:PDA-Ti3C2Tx composite ETL, with higher conductivity and proper work function, can effectively collect electrons in the PSCs. Compared with ZnO control devices, the performance of PSCs with ZnO:PDA-Ti3C2Tx ETL is obviously enhanced with power conversion efficiencies (PCEs) from 10.34% to 12.07% based on PBDB-T:ITIC, 14.84% to 16.69% based on PM6:Y6, and 8.14% to 9.41% for PTB7:PC71BM, respectively. The ambient stability of the PSCs with ZnO:PDA-Ti3C2Tx ETLs is significantly improved due to the increased hydrophobicity of ETL and the enhanced crystallinity of active layer. The novel ETLs provide a facile, eco-friendly, low-cost approach to realize the highly performance and stable PSCs.
... This also has implications in reactivity profiles, namely catalysis in these classes of compounds. [6] Selenium is an important main group element and is present in molecules that find application in materials, [7] in drugs, [8] and in proteins (containing selenocysteine) [9] as well. Over the last few decades, several investigations on chalcogen bonded systems have been performed. ...
The importance of selenium‐centered noncovalent chalcogen bonds represented as Se⋅⋅⋅A (A=O/S) has been explored for short directional contacts in small molecules and proteins. In addition, S⋅⋅⋅O centered contacts have been analyzed. Computational analyses involving the quantitative assessment of the associated energetics, the molecular electrostatic potentials (MEP), and electron density derived topological parameters, namely, quantum theory of atom in molecules (QTAIM) analyses, and NBO (natural bond orbital) based calculations, have been performed to unequivocally establish the strength, stability, and attractive role of chalcogen bonds in the solid‐state. This investigation has been performed in molecules from both the Cambridge Structural Database (CSD) and Protein Data Bank (PDB). Thus futuristic materials may be designed keeping in mind the significance of these interactions, including their relevance in biology.
... Twodimensional (2D) material, which has received enormous scientific interest to date, has also been employed as additive in BHJ-PSC. For example, Huang et al 15 reported that 2D Bi 2 O 2 Se additive can afford additional donor/acceptor interface and effective route for the transfer of charge carriers in the polymer layer. The additive can also encourage the crystallization of the active layer and produce continuous interpenetrating network. ...
Graphitic carbon nitride (g‐C3N4) is a potential additive that can alter the polymer solar cells (PSC) performance. Hereby, we report a novel strategy by applying γ‐radiated g‐C3N4 as additive into bulk heterojunction polymer solar cell (BHJ‐PSC). The incorporation of γ‐radiated g‐C3N4 into the active layer P3HT:PC61BM augments the efficiency of BHJ‐PSC by more than half with respect to the standard undoped device counterpart. The increased performance of γ‐radiated g‐C3N4‐doped BHJ‐PSC is related to increased surface roughness, higher crystallinity, greater optical absorption of the polymer layer and improved charge transfer/recombination dynamics within the device. The optimized BHJ‐PSC containing γ‐radiated g‐C3N4 without encapsulation reaches 2.4% power conversion efficiency (PCE) and the device also retains 60% of the initial PCE even after exposure to high humidity condition (relative humidity 40%‐70%) for 30 days. This suggests that γ‐radiated g‐C3N4 is capable of preventing moisture and oxygen‐induced degradation of P3HT:PC61BM. The γ‐radiated g‐C3N4 additive is also employed in PBDTTT‐C:PCBM polymer system which demonstrates the champion PCE of 2.9%. The present work not only provides an effective strategy for simultaneously enhancing the efficiency and stability of BHJ‐PSC, but also opens up a new horizon for radiation technology and additive engineering.
... Therefore the active layer thickness is a compromise because the thick layer absorbs more light but, at the same time, it increases the charge recombination. Figure 2 shows the graphical representation of the PCE of a P3HT:PCBM-based OSC reported in the literature at its respective active layer thickness [20][21][22][23][28][29][30][31][32][33][34][35][36][37][38][39]. It has been observed that the active layer thickness of less than 100 nm is subjected to poor light absorption while the thicker layer reduces the charge collection capability of the OSC. ...
Due to their low production costs, small weight, printability, solution processing, and the possibility of using flexible substrates, organic solar cells (OSCs) exhibit strong potential to be used in future solar cell technology. Major specifications for the commercialization of OSCs are the long life span of OSC devices, enhanced environmental stability and a sufficiently high power conversion efficiency (PCE). The development of low energy gap organic polymers, transport materials and multi-layer system architecture has been effective in achieving higher PCE. However, overcoming environmental stability and sustaining a longer life span are a major challenge. The instability of OSCs is the dynamic mechanism, mostly induced due to the combined impact of oxygen, incident light, and ambient, as well as processing, temperature. Studies have reported that thermal annealing of the active layer tends to a shift in the phase morphology, which typically occurs either because of the vertical phase separation or because of the process of donor–acceptor phase segregation. In this paper, various factors that affect the performance of the OSC have been comprehensively studied. Factors such as thermal stress, vertical phase segregation, material composition and tradeoff between thickness and light absorption have been discussed. This paper mainly reviews the measures carried out to improve the efficiency of conventional polymer-fullerene-based bulk-heterojunction OSCs and reports the different techniques to address these issues.
This review provides insights into the fundamental properties of bismuth oxychalcogenides Bi2O2X (X = S, Se, Te) (BOXs), with a focus on recent advancements in sensing applications primarily from studies...
With the advent of two‐dimensional (2D) van der Waals (vdW) materials, many non‐van der Waals (nvdW) materials have been synthesized and are being exploited for novel applications. Bismuth oxychalcogenides (Bi 2 O 2 X; X is S, Se, Te), a nvdW series with moderate band gap semiconductors, possess high carrier mobility and air stability. The layers in Bi 2 O 2 X stay with a formal bond, giving rise to distinct structural, optical, thermal, and electronic properties different from conventional vdW materials. Herein, these properties, their synthesis, and transfer methods of 2D Bi 2 O 2 X are examined. The photodetector application of Bi 2 O 2 X and their heterostructure (HS) is surveyed with special attention to Bi 2 O 2 Se. Beyond the photodetector, the other emerging application fields, such as gas‐bio sensors, optoelectronic imaging, integrated memory, solar cells, and photothermal technology of Bi 2 O 2 X are looked over. Based on the ongoing research and challenges, the strategies for future innovations are presented from basics to miniaturized applications. In view of the band offsets of vdW and nvdW semiconductors, the type of HS of a series of 94 vdW‐nvdW sets is proposed. This review will guide future studies on Bi 2 O 2 X and their HS to meet the increasing demands in multifunctional applications from the laboratory to the industrial scale.
Plasmonic biosensing is a label‐free detection method that is commonly used to measure various biomolecular interactions. However, one of the main challenges in this approach is the ability to detect biomolecules at low concentrations with sufficient sensitivity and detection limits. Here, 2D ferroelectric materials are employed to address the issues with sensitivity in biosensor design. A plasmonic sensor based on Bi2O2Se nanosheets, a ferroelectric 2D material, is presented for the ultrasensitive detection of the protein molecule. Through imaging the surface charge density of Bi2O2Se, a detection limit of 1 fM is achieved for bovine serum albumin (BSA). These findings underscore the potential of ferroelectric 2D materials as critical building blocks for future biosensor and biomaterial architectures.
Two-dimensional materials have shown great application potential in high-performance electronic devices because they are ultrathin, have an ultra-large specific surface area, high carrier mobility, efficient channel current regulation, and extraordinary integration. In addition to graphene, other types of 2D nanomaterials have also been studied and applied in photodetectors, solar cells, energy storage devices, and so on. Bi 2 O 2 Se is an emerging 2D semiconductor material with very high electron mobility, modest bandgap, near-ideal subthreshold swing, and excellent thermal and chemical stability. Even in a monolayer structure, Bi 2 O 2 Se has still exhibited efficient light absorption. In this mini review, the latest main research progresses on the preparation methods, electric structure, and the optical, mechanical, and thermoelectric properties of Bi 2 O 2 Se are summarized. The wide rang of applications in electronics and photoelectronic devices are then reviewed. This review concludes with a discussion of the existing open questions/challenges and future prospects for Bi 2 O 2 Se.
Electron transport layers (ETLs) with excellent electron extraction capability are essential for realizing high efficiency in organic solar cells (OSCs). Sol-Gel-processed ZnO ETL is widely used in OSCs due to...
Biomaterials are a new kind of photoelectric materials, which have many advantages. Using biomaterials to adjust the photoelectric properties of active layer in organic solar cells (OSCs) is a new strategy for the preparation of high-performance OSCs. In this work, we add environment-friendly and pollution-free biomaterial astaxanthin (AST) into binary PBDB-T:ITIC system to fabricate the high-efficiency ternary OSCs for the first time. The result show that the addition of AST can not only enhance the crystallization of PBDB-T and ITIC, the absorption intensity of active layer and charge transfer, but also prolong the lifetime and diffusion length of exciton in OSCs. Moreover, there exists the Förster resonant energy transfer (FRET) between energy donor AST and the energy accepter (PBDB-T), which promotes the generation of excitons. Therefore, by adding 0.1 wt% AST, the power conversion efficiency (PCE) of ternary OSCs is obviously increased from 10.27% to 12.07% for PBDB-T:ITIC system. In addition, the ternary OSCs shows higher device storage stability due to its stable morphology and crystallization. This work shows that the clean and pollution-free biomaterial AST can effectively improve the performance of OSCs, which paves the way for the development of environmentally friendly OSCs with high efficiency and stability.
In organic solar cells (OSCs), the crystalline morphologies of the donor and acceptor at the microscale play an important role. 2D GeSe with periodic structure and high carrier mobility is an ideal additive material for active layer of OSCs that can effectively improve the crystallinity and molecular orientation of the acceptor molecule ITIC. Here, 2D GeSe is introduced into the active layer of OSCs to adjust the morphology of active layer for the first time, the results show that the incorporation of 2D GeSe induces the crystallization of acceptor molecule and facilitates the formation of efficient bicontinuous interpenetrating charge transport networks, and effectively reduces carrier recombination in OSCs. The power conversion efficiency and lifetime of OSCs are obviously enhanced. More importantly, the results of first‐principles calculation reveal that the interaction between 2D GeSe and ITIC guides the ITIC molecules to form a continuous conductive network. This study provides a method for the morphology regulation of the donor and acceptor domains in bulk heterojunctions, provides an idea for researching the interaction between 2D materials and organic molecules, and also indicates that 2D GeSe has good application prospects in photovoltaic devices.
Recently, layered oxychalcogenides have been extensively studied as promising thermoelectric materials. These materials have ionic oxide with alternative covalent chalcogenide layers, resulting in many interesting electronic properties. The materials also enable the tuning of their properties via chemical substitutions at the coexisting layers. Recently, bismuth (Bi)-based oxychalcogenides have attracted many scientists from the field of material research because of their distinctive structure, high carrier mobility, and excellent environmental stability, making them suitable candidates for high-performance electronic and optoelectronic applications. In this present report, we have presented a comprehensive review of recently developed Bi-based oxychalcogenides. The simplest Bi-oxychalcogenides are in the ternary form (Bi2O2Ch, Ch = S, Se, Te). We start with an introduction and classify the compounds based on sulphide, selenide, and telluride with their fundamental properties. In addition to that, different synthesis methods of oxychalcogenides along with their applications are discussed in detail. Different device applications of related materials, including photodetectors, transistors, optical switches, and artificial synapses, are also presented.
The prominent light-matter interaction in 2D materials has become a pivotal research area that involves either an archetypal study of inherent mechanisms to explore such interactions or specific applications to assess the efficacy of such novel phenomena. With scientifically controlled light-matter interactions, various applications have been developed. Here, we report four diverse applications on a single structure utilizing the efficient photoresponse of Bi2O2Se with precisely tuned multiple optical wavelengths. First, the Bi2O2Se-based device performs the function of optoelectronic memory using UV (λ = 365 nm, 1.1 mW cm-2) for the write-in process with SiO2 as the charge trapping medium followed by a +1 V bias for read-out. Second, associative learning is mimicked with wavelengths of 525 nm and 635 nm. Third, using similar optical inputs, functions of logic gates "AND", "OR", "NAND", and "NOR" are realized with response current and resistance as outputs. Fourth is the demonstration of a 4 bit binary to the decimal converter using wavelengths of 740 nm (LSB), 595 nm, 490 nm, and 385 nm (MSB) as binary inputs and output response current regarded as equivalent decimal output. Our demonstration is a paradigm for Bi2O2Se-based devices to be an integral part of future advanced multifunctional electronic systems.
Totally understanding the excitons dissociation in nonfullerene organic solar cells (OSCs) is the first priority for the minimum of the device energy loss and so that it can get the highest power conversion efficiency (PCE). The free charges harvesting is complicated though it has already published some evident examples to investigate this issue by small driving force between donors (D) and accepters (A). Here, a robust minus highest occupied molecular orbital (HOMO) level offset D-A couple unveiled this phenomena in greater depth by a time-resolved photo physical processes. The OSCs D-A heterojunction interfacial doping resonant coupling relaxation effect was observed and found some clues with device open-circuit voltage (Voc) energy loss. It undoubtedly demonstrated the device PCE up to 2.37% by a −0.12 eV HOMO offsets value. It was also found that the donor polymer aggregation behavior was greatly affected by the small molecular acceptor. These results will be beneficial to promote the OSCs comprehensive properties in future.
Sensible selection of host blends and the third component is crucial to give full play to the advantages of the ternary strategy for achieving high efficiency polymer solar cells (PSCs). In this work, a PM6:BTP-BO-4Cl binary system and non-fullerene acceptor DTTC-4ClC9 with the dithienocyclopentacarbazole (DTC) core are selected as the host blend and the third component, respectively. DTTC-4ClC9 and BTP-BO-4Cl are found to have excellent miscibility, and the addition of DTTC-4ClC9 into the binary blend can modify the morphology of the film, which brings out an improved charge transport and obviously enhanced exciton dissociation ability. The non-radiative energy loss of the devices is significantly reduced to 0.207 eV when employing the ternary strategy, thus leading to a reduction in energy loss. As a result, the introduction of 15% DTTC-4ClC9 in the PM6:BTP-BO-4Cl system can promote the power conversion efficiency from 17.11% to remarkable 18.21%, meanwhile, the open-circuit voltage, short-circuit current density, and fill factor are increased simultaneously.
The thin-film organic solar cells (OSCs) are currently one of the most promising photovoltaic technologies to effectively harvest the solar energy due to their attractive features of mechanical flexibility, light weight, low-cost manufacturing, and solution-processed large-scale fabrication, etc. However, the relative insufficient light absorption, short exciton diffusion distance, and low carrier mobility of the OSCs determine the power conversion efficiency (PCE) of the devices are relatively lower than their inorganic photovoltaic counterparts. To conquer the challenges, the two-dimensional (2D) nanomaterials, which have excellent photoelectric properties, tunable energy band structure, and solvent compatibility etc., exhibit the great potential to enhance the performance of the OSCs. In this review, we summarize the most recent successful applications of the 2D materials, including graphene, black phosphorus, transition metal dichalcogenides, and g-C3N4, etc., adapted in the charge transporting layer, the active layer, and the electrode of the OSCs, respectively, for boosting the PCE and stability of the devices. The strengths and weaknesses of the 2D materials in the application of OSCs are also reviewed in details. Additionally, the challenges, commercialization potentials, and prospects for the further development of 2D materials-based OSCs are outlined in the end.
Additive modification can be a meritorious method for performance enhancement of perovskite solar cells (PSCs). In this work, as a superior charge carrier transportation material, WS2 quantum dots in anti-solvent are generated by pulsed laser irradiation and subsequently embedded in perovskite film to reduce the grain boundary barriers and accelerate charge transport via favorable band alignment, as can be proved by ultraviolet photoelectron spectroscopy (UPS). Besides, X-ray photoelectron spectroscopy (XPS) tests reveal the interaction of WS2 quantum dots with Pb²⁺ via Pb–S bonds, indicating the suppressed uncoordinated Pb²⁺ trap states. Thus, the reduced defects and superior band alignment in PSCs will lead to the decreased charge recombination and excellent charge transport, which can improve the efficiency of PSCs. As a result, the highest power conversion efficiency (PCE) of 16.85% is obtained through WS2 quantum dots modification with an optimum concentration of 0.1 mg/mL in anti-solvent, which is substantially promoted when compared with the pristine PSCs (13.27%). Moreover, the modified device sample can still keep 71% of the original PCE after 50-day conservation indoor with a humidity of 30–50%. This work can provide a novel fast and convenient method for WS2 quantum dots fabrication and the potential applications in PSCs.
The interfacial modification with biomaterials is an effective and environmental protection way to improve the efficiency of inverted polymer solar cells (IPSCs) by reducing the defects and interface recombination of ZnO electron transport layer (ETL). In this paper, ZnO surface is successfully modified via Gly-His-Lys-Cu (GHK-Cu), a nontoxic biomaterial, to fabricate novel ZnO&GHK-Cu composite film. The modification of ZnO surface by GHK-Cu makes the Zn-O-Cu bond formed on the surface of ZnO, which provides a channel for the electron transfer from electron-rich functional groups (such as carboxyl, amino and carbonyl) to Zn²⁺, the electron defects caused by the oxygen vacancies in the ZnO lattice are passivated, which is beneficial to the transfer and extraction of charges in IPSCs. Moreover, the modification of GHK-Cu decreases the chemisorbed oxygen of the surface of ZnO, the height of the Schottky barrier between the ZnO crystal grains is reduced, resulting in an increase in the conductivity of ZnO. The novel ZnO&GHK-Cu composite film has excellent photoelectric properties and IPSCs with new ZnO&GHK-Cu as ETL are fabricated for the first time. As the result, the IPSCs based on PBDB-T:ITIC with ZnO&GHK-Cu as ETL show an optimal power conversion efficiency (PCE) of 11.93%, increases by 15.6% in comparison with ZnO ETL-based IPSCs with a PCE of 10.32%. Meanwhile, the PCE of IPSCs based on PM6:Y6 increases from 14.66% to 16.46%. More interesting, the physical mechanism of improving the performance of IPSCs by modifying of ZnO surface with biomaterial has been deeply analyzed. The work provides an effective method for modification of ZnO surface, also shows that biomaterial GHK-Cu has application prospect in photovoltaic devices.
In this paper, we demonstrate a solution-processed MoSe2quantum dots/PEDOT:PSS bilayer hole extraction layer (HEL) for non-fullerene organic solar cells (OSCs). It is found that the introduction of MoSe2QDs can alter the work function and phase separation of PEDOT:PSS, thus affecting the morphology of the active layer and improving the performance of OSCs. The MoSe2QDs/PEDOT:PSS bilayer HEL can improve the fill factor (FF), short-circuit current density (Jsc) and power conversion efficiency (PCE) of OSCs based on different active layers. The best PCE of up to 17.08% was achieved based on a recently reported active layer binary system named SZ2:N3, which is among the highest reported values to date for OSCs using 2D materials as an interface modifier. Our study indicates that this simple and solution-processed MoSe2QDs/PEDOT:PSS bilayer thin film could be a potential alternative HEL to the commonly used PEDOT:PSS conducting polymers.
Due to the simple structure and excellent scalability, regioregular poly(3-hexylthiophene) (P3HT) has become much more popular as a low-cost donor polymer partner with the emerging nonfullerene acceptors in recent years. Presently, the application and the molar mass dependence of direct arylation polycondensation (DArP) prepared P3HT in fullerene-free organic solar cells have not been explored yet. In this work, five batches of P3HT with weight-average molar mass ranging from 8.9 kg mol⁻¹to 89.1 kg mol⁻¹were successfully preparedviaDArP, with the aim to detail the interaction-performance relationships in the state-of-the-art P3HT:nonfullerene photovoltaic blend, namely P3HT:ZY-4Cl. Our thermodynamic analysis revealed that the amorphous-amorphous interaction parameters strongly depend on the P3HT molar mass and can be varied by a factor of 2.75. Owing to the best π-π stacking order deduced from grazing incidence X-ray diffraction and the smallest domain size, the blend based on the medium molar mass batch (25.5 kg mol⁻¹) delivered the highest current density, fill factor, and power conversion efficiency up to ∼10% among the five systems. Our study confirmed that DArP is an effective protocol for the synthesis of P3HT for efficient non-fullerene polymer solar cells and the established relationships can be applied to screen the best batch for P3HT-based organic photovoltaics.
Additive passivation can be an effective strategy to regulate and control the properties of organic-inorganic halide perovskite film. In this article, carbon quantum dots (CQDs), fabricated by non-focused laser irradiation of carbon nanomaterial diluted in anti-solvent ethyl acetate, denoted as EACQDs, were adopted for perovskite film defect passivation and modification of carbon-based CH3NH3PbI3 perovskite solar cells (PSCs). The size of EACQDs can be tuned by manipulating the laser fluence. The morphology of perovskite film was uncovered through scanning electron microscopy and atomic force microscopy. After embedding of EACQDs, the defect in perovskite crystal was reduced, resulting in the decreased carrier recombination and accelerated carrier transportation, which were demonstrated by electrochemical impedance spectroscopy, photoluminescence and time-resolved photoluminescence. As a consequence, with the optimization of 0.01 mg/mL EACQDs (1064 nm-300 mJ.pulse⁻¹.cm⁻²-10 min), the power conversion efficiency (PCE) of carbon-based PSCs achieved a maximum value of 16.43%, which improved 23.81% when compared with the pristine PSCs of 13.27%. Furthermore, the EACQDs optimized PSCs also exhibited an excellent stability and still retained 86% of its initial PCE after 50-day storage at the room atmosphere with a humidity of 30%∼50%.
The n-type metallic oxide SnO2 exists surface energy band bending due to massive vacancy oxygen. The bending will cause unnecessary electron accumulation and recombination at the interface between electron transport layer (ETL) and perovskite layer. Besides, there exist massive deep-level defects (PbI, Pbi, IPb) for solution-processed polycrystalline perovskite films, which will aggravate the energy band uncoordinated and non-radiative recombination, limiting device efficiency and stability. Herein, amphoteric linking molecule p-amino benzenesulfonic acid (ABSA) is firstly used to synergistically modify the interface between SnO2 ETL and perovskite layer. The acidic sulfonic acid groups in ABSA modify SnO2 ETL by inactivating the under-coordinated Sn ions, which reduces the energy band barrier on the surface of SnO2 film, increasing the conduction and reduces charge recombination. Besides, the alkaline amino groups also passivate the deep-level defects on surface of perovskite to lessen intermediate energy level and non-radiative recombination. The power conversion efficiency (PCE) of perovskite solar cells (PSCs) based on MAPbI3 is obviously increased from 18.02% to 20.32% after 0.10 mg ml⁻¹ ABSA modification. Simultaneously, the modified devices show better stability due to improved perovskite crystallization and the reduced defects. The energy band model for SnO2 nanoparticle and interface between perovskite layer and SnO2 ETL is established to explain the interfacial engineering from a new physical perspective.
Two-dimensional (2D) Bi2O2Se that exhibits high carrier mobility, moderate band gap, and good stability is a promising candidate of 2D semiconductors for next-generation computing technologies. However, the electronic properties of ultrathin Bi2O2Se films are poorly understood, especially the thickness and strain tunability of their electronic structures. In this work, we performed a systematic investigation of electronic structures of 2D Bi2O2Se using HSE06 method with high accuracy. Our results show that Bi2O2Se multi-layers display a weak quantum size effect. The origin of this unusual phenomenon is elucidated by the crystal orbital Hamilton population (COHP) analysis. Imposed with biaxial strain, band gaps of monolayer and bilayer can be modulated in a large energy range, e.g., direct band gap of monolayer from 3.08 eV to 1.17 eV which strides over the whole visible light region. Besides, the band gap of bilayer closes up at large tensile strain of ~8%, indicating a semiconductor-metal transition. Further analysis of valence band and conduction band edges shows that high tunability of band gap originates from the sensitivity of band edge with strain, especially conduction band minimum. With the strain from compressive to tensile, Bi-Se bond length gradually increase with the stretch of lattice, which reduces the Bi-Se bond strength and thus lowers the energies of valence band and conduction band edge states due to their antibonding character. Highly tunable electronic properties via changing thickness or adding strain impart Bi2O2Se more possibilities for its application in electronic and optoelectronic devices.
Due to the excellent electrical and optical properties, few-layered β-indium selenide (InSe) nanosheets are successfully introduced into the active layer of polymer solar cells (PSCs) as the third component for the first time. The addition of few-layered β-InSe nanosheets optimizes the absorption, crystallinity and vertical component distribution of the active layer. Compared with the binary devices, the ternary devices exhibit optimized bulk morphology and reduced charge recombination. The power conversion efficiency (PCE) of PSCs based on the PM6 : Y6 system is obviously improved from 15.02% to 16.56% due to the increasing short-circuit current and fill factor. The mechanism accounting for the morphological change in the ternary active layer is investigated in depth. Moreover, the efficacy of β-InSe in long-term stability and other active layer systems of PSCs is confirmed. Therefore, this work demonstrates that few-layered β-InSe has bright prospects in photovoltaic devices.
Two-dimensional Bi2O2Se has drawn a lot of attention recently, due to its ultrahigh mobility and excellent performance in electronics and optoelectronics. However, the facile synthesis of two-dimensional Bi2O2Se nanocrystals is urgently required for their fundamental study and practical applications. In this work, we develop a controllable synthetic route to ultrathin Bi2O2Se nanosheets through the assistance of lithium nitrate (LiNO3) in a hydrothermal process. TEM, AFM, XRD, XPS and Raman demonstrate the successful synthesis of ultrathin Bi2O2Se nanosheets with a tetragonal phase. With Li⁺ adsorbing on {001} facets to inhibit crystal growth along the [001] direction, the lateral size of the Bi2O2Se nanosheets can be controlled through the amount of LiNO3 in the system. Photoelectrochemical tests reveal the good performance of the ultrathin Bi2O2Se nanosheets as a photoanode material in neutral solution. Detailed analysis of electrochemical impedance spectra and specific surface areas reveals that a high surface area and low recombination rate are responsible for the good photoelectrochemical activity of the larger Bi2O2Se nanosheets. Besides, the stability test shows negligible reduction of current density after 10 hours, and the TEM test demonstrates that the structure of the Bi2O2Se nanosheets is well preserved after long-term electrolysis, revealing great stability of the Bi2O2Se nanosheets as a photoanode material. This work indicates that two-dimensional Bi2O2Se could be a competitive candidate for the future energy systems.
Additive engineering has been proved to be an effective method to increase the performance of perovskite solar cells (PVSCs) by increasing the quality of the perovskite thin film. Two-dimensional (2D) Bi2OS2 nanomaterial is an excellence optoelectronic material because of its tunable direct band gap, ultra-high charge mobility, wide absorption range and high absorption coefficient. In this work, 2D Bi2OS2 nanosheets are synthesized and introduced as additives into the perovskite precursor solution to adjust the film formation process for the first time. Serving as heterogeneous nucleation site, 2D Bi2OS2 can reduce the nucleation barrier and assist the formation of highly crystalline and crystal orientation along the (1 1 0) plane perovskite thin film, which is beneficial to improve the mobility and lifetime of charge carriers. Besides, X-ray photoelectron spectroscopy (XPS) measurement reveals that 2D Bi2OS2 nanosheets can interact with Pb²⁺ within the perovskite through Pb-S bond, thus suppressing the uncoordinated Pb²⁺ ions trap states. Scanning electron microscope (SEM) demonstrates 2D Bi2OS2 nanosheets can fill up the pin-holes and grain boundaries on the perovskite film surface. Ultraviolet photoelectron spectroscopy (UPS) measurement indicates that the valence band (VB) of optimized perovskite film is 0.28 eV upshifted closer to the highest occupied molecular orbital (HOMO) of the hole transport layer (HTL), which accelerates the charge transportation at perovskite/HTL interface. Consequently, the average power conversion efficiency (PCE) of 18.96% (highest PCE of 19.89%) is achieved upon incorporating 2D Bi2OS2 nanosheets with an optimized concentration of 0.02 mg/ml into MAPbI3 precursor solution, which is greatly improved compared to the average PCE of 15.71% for the control devices (highest PCE of 16.77%). Besides, the lifetime of optimized PVSCs is also prolonged due to the less defect states and better perovskite film quality. This work not only provides a facile method to increase the PCE and stability of PVSCs, but also reveals 2D Bi2OS2 material has potential applications in PVSCs.
The study of 2D materials has been a significant and fascinating area, at least since the discovery of graphene. As one of the layered bismuth oxychalcogenides, bismuth oxyselenide (Bi2O2Se) has drawn a lot of attention recently. The study of Bi2O2Se was mainly focused on its thermoelectric performance until its ultrathin 2D structure came to the fore. New physical properties of Bi2O2Se were discovered along with the successful synthesis of 2D Bi2O2Se structures. Few‐layer Bi2O2Se exhibits ultrahigh mobility, outstanding stability, tunable bandgaps, and excellent mechanical properties, showing remarkable performance in electronics and optoelectronics. In this report, an overview of recent advances in Bi2O2Se research is provided, including structure/property modifications, synthetic methods, and practical applications. Theoretical and experimental results on bulk/few‐layer Bi2O2Se are both discussed in this report. Finally, the challenges and outlook for Bi2O2Se are evaluated based on current progress. As a new emerging 2D material, Bi2O2Se has shown remarkable properties. Herein, an overview of the research progress for Bi2O2Se is provided. The turnability of structure/property, preparation methods, and various applications of 2D Bi2O2Se are all discussed in this report. Bi2O2Se exhibits excellent properties for potential applications in many areas.
Controlling the morphological stability of non-fullerene polymer solar cells (NF-PSCs) is a critical process for improving photovoltaic performances. In many systems, liquid additives have been widely used to produce favorable morphological features; however, liquid additives frequently left residues after thermal treatment owing to their high boiling points, which had detrimental effects on the reproducibility of NF-PSCs. In this study, commercially available and volatilizable solid additives, 9,10-anthracenedione (BDT-1) and benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BDT-2), are selected to coordinate molecular arrangement to enhance absorption intensity, charge transfer, and molecular crystallinity. Suppressed bimolecular recombination and favorable balance between the domain size and relative domain purity were observed by the introduction of both solid additives, which improved the photovoltaic parameters of NF-PSCs. PM6:TPT10-based devices with BDT-1 and BDT-2 additives achieved the best power conversion efficiencies (PCEs) of 16.26% and 15.18%, respectively, which were better than 13.55% achieved with a 1,8-diiodooctane (DIO) additive. Other NF-PSC systems of PBDB-T:TPT10 and PTQ10:TPT10 blends also showed that the photovoltaic performance with the solid additives is superior to that with liquid additives. These results imply that the use of solid additives is a promising strategy to improve PCEs of NF-PSCs.
The use of a ternary active layer offers a promising approach to enhance the power conversion efficiency (PCE) of polymer solar cells (PSCs) via simply incorporating a third component. Here, a ternary PSC with improved efficiency and stability facilitated by a new small molecule IBC‐F is demonstrated. Even though the PBDB‐T:IBC‐F‐based device gives an extremely low PCE of only 0.21%, a remarkable PCE of 15.06% can be realized in the ternary device based on PBDB‐T:IE4F‐S:IBC‐F with 20% IBC‐F, which is ≈10% greater than that (PCE = 13.70%) of the control binary device based on PBDB‐T:IE4F‐S. The improvement in the device performance of the ternary PSC is mainly attributed to the enhancement of fill factor, which is due to the improved charge dissociation and extraction, suppressed bimolecular and trap‐assisted recombination, longer charge‐carrier lifetime, and enhanced intermolecular interactions for preferential face‐on orientation. Additionally, the ternary device with 20% IBC‐F shows better thermal and photoinduced stability over the control binary device. This work provides a new angle to develop the third components for building ternary PSCs with enhanced photovoltaic performance and stability for practical applications.
Ternary heterojunction strategies appear to be an efficient approach to improve the efficiency of organic solar cells (OSCs) through harvesting more sunlight. Ternary OSCs are fabricated by employing wide bandgap polymer donor (PM6), narrow bandgap nonfullerene acceptor (Y6), and PC71BM as the third component to tune the light absorption and morphologies of the blend films. A record power conversion efficiency (PCE) of 16.67% (certified as 16.0%) on rigid substrate is achieved in an optimized PM6:Y6:PC71BM blend ratio of 1:1:0.2. The introduction of PC71BM endows the blend with enhanced absorption in the range of 300–500 nm and optimises interpenetrating morphologies to promote photogenerated charge dissociation and extraction. More importantly, a PCE of 14.06% for flexible ITO‐free ternary OSCs is obtained based on this ternary heterojunction system, which is the highest PCE reported for flexible state‐of‐the‐art OSCs. A very promising ternary heterojunction strategy to develop highly efficient rigid and flexible OSCs is presented. High efficiencies of 16.67% (certified as 16.0%) for rigid and 14.06% for flexible organic solar cells (OSCs) are achieved by employing a PM6:Y6:PC71BM ternary system. This is a promising ternary heterojunction strategy for the development of highly efficient rigid and flexible OSCs.
Organic light-emitting diode (OLED) technology is promising for applications in next-generation displays and lighting. However, it is difficult—especially in large-area mass production—to cover a large substrate uniformly with organic layers, and variations in thickness cause the formation of shunting paths between electrodes1,2, thereby lowering device production yield. To overcome this issue, thicker organic transport layers are desirable because they can cover particles and residue on substrates, but increasing their thickness increases the driving voltage because of the intrinsically low charge-carrier mobilities of organics. Chemical doping of organic layers increases their electrical conductivity and enables fabrication of thicker OLEDs3,4, but additional absorption bands originating from charge transfer appear⁵, reducing electroluminescence efficiency because of light absorption. Thick OLEDs made with organic single crystals have been demonstrated⁶, but are not practical for mass production. Therefore, an alternative method of fabricating thicker OLEDs is needed. Here we show that extraordinarily thick OLEDs can be fabricated by using the organic–inorganic perovskite methylammonium lead chloride, CH3NH3PbCl3 (MAPbCl3), instead of organics as the transport layers. Because MAPbCl3 films have high carrier mobilities and are transparent to visible light, we were able to increase the total thickness of MAPbCl3 transport layers to 2,000 nanometres—more than ten times the thickness of standard OLEDs—without requiring high voltage or reducing either internal electroluminescence quantum efficiency or operational durability. These findings will contribute towards a higher production yield of high-quality OLEDs, which may be used for other organic devices, such as lasers, solar cells, memory devices and sensors.
Ternary organic solar cells (OSCs) are among the best‐performing organic photovoltaic devices to date, largely due to the recent development of nonfullerene acceptors. However, fullerene molecules still play an important role in ternary OSC systems, since, for reasons not well understood, they often improve the device performance, despite their lack of absorption. Here, the photophysics of a prototypical ternary small‐molecule OSC blend composed of the donor DR3, the nonfullerene acceptor ICC6, and the fullerene derivative PC71BM is studied by ultrafast spectroscopy. Surprisingly, it is found that after excitation of PC71BM, ultrafast singlet energy transfer to ICC6 competes efficiently with charge transfer. Subsequently, singlets on ICC6 undergo hole transfer to DR3, resulting in free charge generation. Interestingly, PC71BM improves indirectly the electron mobility of the ternary blend, while electrons reside predominantly in ICC6 domains as indicated by fast spectroscopy. The improved mobility facilitates charge carrier extraction, in turn leading to higher device efficiencies of the ternary compared to binary solar cells. Using the (photo)physical parameters obtained from (transient) spectroscopy and charge transport measurements, the device's current–voltage characteristics are simulated and it is demonstrated that the parameters accurately reproduce the experimentally measured device performance.
Ternary approaches to solar cell design utilizing a small bandgap nonfullerene acceptor as the near infrared absorber to increase the short‐circuit current density always decreases the open‐circuit voltage. Herein, a highly efficient polymer solar cell with an impressive efficiency of 16.28 ± 0.20% enabled by an effective voltage‐increased ternary blended fullerene‐free material approach is reported. In this approach, the structural similarity between the host and the higher‐LUMO‐level guest enables the two acceptors to be synergized, obtaining increased open‐circuit voltage and fill factor and a small increase of short‐circuit current density. The same beneficial effects are demonstrated by using two host binary systems. The homogeneous fine film morphologies and the π–π stacking patterns of the host blend are well maintained, while larger donor and acceptor phases and increased lamellar crystallinity, increased charge mobilities, and reduced monomolecular recombination can be achieved upon addition of the guest nonfullerene acceptor. The increased charge mobilities and reduced monomolecular recombination not only contribute to the improved fill factor but also enable the best devices to be fabricated with a relatively thicker ternary blended active layer (110 vs 100 nm). This, combined with the absorption from the added guest acceptor, contribute to the increased short‐circuit current.
Recent advances in the material design and synthesis of nonfullerene acceptors (NFAs) have revealed a new landscape for polymer solar cells (PSCs) and have boosted the power conversion efficiencies (PCEs) to over 15%. Further improvements of the photovoltaic performance are a significant challenge in NFA‐PSCs based on binary donor:acceptor blends. In this study, ternary PSCs are fabricated by incorporating a fullerene derivative, PC61BM, into a combination of a polymer donor (PBDB‐TF) and a fused‐ring NFA (Y6) and a very high PCE of 16.5% (certified as 16.2%) is recorded. Detailed studies suggest that the loading of PC61BM into the PBDB‐TF:Y6 blend can not only enhance the electron mobility but also can increase the electroluminescence quantum efficiency, leading to balanced charge transport and reduced nonradiative energy losses simultaneously. This work suggests that utilizing the complementary advantages of fullerene and NFAs is a promising way to finely tune the detailed photovoltaic parameters and further improve the PCEs of PSCs. Ternary polymer solar cells are successfully developed by combining a fullerene derivative and a nonfullerene material as acceptors. The introduction of PC61BM into the PBDB‐TF:Y6 blend effectively improves the charge transport properties and reduces the nonradiative energy loss. Ultimately, the main photovoltaic parameters are simultaneously enhanced in the ternary devices, leading to an outstanding efficiency of 16.5% (certificated as 16.2%).
Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency. Halogenation has proved an effective strategy to improve the power conversion efficiencies of organic solar cells but it usually leads to lower open-circuit voltages. Here, Cui et al. unexpectedly obtain higher open-circuit voltages and achieve a record high PCE of 16.5% by chlorination.
Vertically aligned zinc oxide nanorod arrays (ZnO NRAs) are expected to provide a direct and stable electron transport pathway in polymer solar cells (PSCs) so as to enhance charge carrier...
Atomically thin 2D materials have received intense interest both scientifically and technologically. Bismuth oxyselenide (Bi2O2Se) is a semiconducting 2D material with high electron mobility and good stability, making it promising for high‐performance electronics and optoelectronics. Here, an ambient‐pressure vapor–solid (VS) deposition approach for the growth of millimeter‐size 2D Bi2O2Se single crystal domains with thicknesses down to one monolayer is reported. The VS‐grown 2D Bi2O2Se has good crystalline quality, chemical uniformity, and stoichiometry. Field‐effect transistors (FETs) are fabricated using this material and they show a small contact resistivity of 55.2 Ω cm measured by a transfer line method. Upon light irradiation, a phototransistor based on the Bi2O2Se FETs exhibits a maximum responsivity of 22 100 AW⁻¹, which is a record among currently reported 2D semiconductors and approximately two orders of magnitude higher than monolayer MoS2. The Bi2O2Se phototransistor shows a gate tunable photodetectivity up to 3.4 × 10¹⁵ Jones and an on/off ratio up to ≈10⁹, both of which are much higher than phototransistors based on other 2D materials reported so far. The results of this study indicate a method to grow large 2D Bi2O2Se single crystals that have great potential for use in optoelectronic applications.
Recently, the advent of non-fullerene acceptors (NFAs) made it possible for organic solar cells (OSCs) to break the 10% efficiency barrier hardly attained by fullerene acceptors (FAs). In the past five years alone, more than hundreds of NFAs with applications in organic photovoltaics (OPVs) have been synthesized, enabling a notable current record efficiency of above 15%. Hence, there is a shift in interest towards the use of NFAs in OPVs. However, there has been little work on the stability of these new materials in devices. More importantly, there is very little comparative work on the photo-stability of FAs vs. NFAs solar cells, to ascertain the pros and cons of the two systems. Here, we show the photo-stability of solar cells based on two workhorse acceptors, in both conventional and inverted structures, namely ITIC (as NFA) and [70]PCBM (as FA) blended with either PBDB-T or PTB7-Th polymer. We found that irrespective of the polymer, the cell structure, or the initial efficiency, the [70]PCBM devices are more photo-stable than the ITIC ones. This observation, however, opposes the assumption that NFA solar cells are more photo-chemically stable. These findings suggest that complementary absorption should not take precedence in the design rules for the synthesis of new molecules and there is still work left to be done to achieve stable as well as efficient OSCs.
The efficiency of organic solar cells can benefit from multijunction device architectures, in which energy losses are substantially reduced. Herein, recent developments in the field of solution‐processed multijunction organic solar cells are described. Recently, various strategies have been investigated and implemented to improve the performance of these devices. Next to developing new materials and processing methods for the photoactive and interconnecting layers, specific layers or stacks are designed to increase light absorption and improve the photocurrent by utilizing optical interference effects. These activities have resulted in power conversion efficiencies that approach those of modern thin film photovoltaic technologies. Multijunction cells require more elaborate and intricate characterization procedures to establish their efficiency correctly and a critical view on the results and new insights in this matter are discussed. Application of multijunction cells in photoelectrochemical water splitting and upscaling toward a commercial technology is briefly addressed. Multijunction organic solar cells provide higher power conversion efficiencies than the corresponding single junction solar cells by reducing thermalization and transmission losses and are fabricated by sequential layer deposition from solution. In recent years, important progress is made in terms of novel materials and device design and the most salient advances are discussed in this review.
Solution‐processed small molecule (SM) solar cells have the prospect to outperform their polymer‐fullerene counterparts. Considering that both SM donors/acceptors absorb in visible spectral range, higher expected photocurrents should in principle translate into higher power conversion efficiencies (PCEs). However, limited bulk‐heterojunction (BHJ) charge carrier mobility (<10‐4 cm² V‐1 s‐1) and carrier lifetimes (<1 µs) often impose active layer thickness constraints on BHJ devices (≈100 nm), limiting external quantum efficiencies (EQEs) and photocurrent, and making large‐scale processing techniques particularly challenging. In this report, it is shown that ternary BHJs composed of the SM donor DR3TBDTT (DR3), the SM acceptor ICC6 and the fullerene acceptor PC71BM can be used to achieve SM‐based ternary BHJ solar cells with active layer thicknesses >200 nm and PCEs nearing 11%. The examinations show that these remarkable figures are the result of i) significantly improved electron mobility (8.2 × 10‐4 cm² V‐1 s‐1), ii) longer carrier lifetimes (2.4 µs), and iii) reduced geminate recombination within BHJ active layers to which PC71BM has been added as ternary component. Optically thick (up to ≈500 nm) devices are shown to maintain PCEs >8%, and optimized DR3:ICC6:PC71BM solar cells demonstrate long‐term shelf stability (dark) for >1000 h, in 55% humidity air environment.
Semiconductors are essential materials that affect our everyday life in the modern world. Two-dimensional semiconductors with high mobility and moderate bandgap are particularly attractive today because of their potential application in fast, low-power, and ultrasmall/thin electronic devices. We investigate the electronic structures of a new layered air-stable oxide semiconductor, Bi 2 O 2 Se, with ultrahigh mobility (~2.8 × 10 ⁵ cm ² /V⋅s at 2.0 K) and moderate bandgap (~0.8 eV). Combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy, we mapped out the complete band structures of Bi 2 O 2 Se with key parameters (for example, effective mass, Fermi velocity, and bandgap). The unusual spatial uniformity of the bandgap without undesired in-gap states on the sample surface with up to ~50% defects makes Bi 2 O 2 Se an ideal semiconductor for future electronic applications. In addition, the structural compatibility between Bi 2 O 2 Se and interesting perovskite oxides (for example, cuprate high–transition temperature superconductors and commonly used substrate material SrTiO 3 ) further makes heterostructures between Bi 2 O 2 Se and these oxides possible platforms for realizing novel physical phenomena, such as topological superconductivity, Josephson junction field-effect transistor, new superconducting optoelectronics, and novel lasers.
Herein, efficient organic solar cells (OSCs) are realized with the ternary blend of a medium band gap donor (poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione)] (PBDB‐T)) with a low band gap acceptor (2,2′‐((2Z,2′Z)‐(((2,5‐difluoro‐1,4‐phenylene)bis(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐6,2‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (HF‐PCIC)) and a near‐infrared acceptor (2,2′‐((2Z,2′Z)‐(((4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(4‐((2‐ethylhexyl)oxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IEICO‐4F)). It is shown that the introduction of IEICO‐4F third component into PBDB‐T:HF‐PCIC blend increases the short‐circuit current density (J sc) of the ternary OSC to 23.46 mA cm⁻², with a 44% increment over those of binary devices. The significant current improvement originates from the broadened absorption range and the active layer morphology optimization through the introduction of IEICO‐4F component. Furthermore, the energy loss of the ternary cells (0.59 eV) is much decreased over that of the binary cells (0.80 eV) due to the reduction of both radiative recombination from the absorption below the band gap and nonradiative recombination upon the addition of IEICO‐4F. Therefore, the power conversion efficiency increases dramatically from 8.82% for the binary cells to 11.20% for the ternary cells. This work provides good examples for simultaneously achieving both significant current enhancement and energy loss mitigation in OSCs, which would lead to the further construction of highly efficient ternary OSCs.
Fullerenes have formed an integral part of high performance organic solar cells over the last 20 years, however their inherent limitations in terms of synthetic flexibility, cost and stability have acted as a motivation to develop replacements; the so-called non-fullerene electron acceptors. A rapid evolution of such materials has taken place over the last few years, yielding a number of promising candidates that can exceed the device performance of fullerenes and provide opportunities to improve upon the stability and processability of organic solar cells. In this review we explore the structure–property relationships of a library of non-fullerene acceptors, highlighting the important chemical modifications that have led to progress in the field and provide an outlook for future innovations in electron acceptors for use in organic photovoltaics.
In this work, a nonfullerene polymer solar cell (PSC) based on a wide bandgap polymer donor PM6 containing fluorinated thienyl benzodithiophene (BDT-2F) unit and a narrow bandgap small molecule acceptor 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) is developed. In addition to matched energy levels and complementary absorption spectrum with IDIC, PM6 possesses high crystallinity and strong π–π stacking alignment, which are favorable to charge carrier transport and hence suppress recombination in devices. As a result, the PM6:IDIC-based PSCs without extra treatments show an outstanding power conversion efficiency (PCE) of 11.9%, which is the record value for the as-cast PSC devices reported in the literature to date. Moreover, the device performances are insensitive to the active layer thickness (≈95–255 nm) and device area (0.20–0.81 cm²) with PCEs of over 11%. Besides, the PM6:IDIC-based flexible PSCs with a large device area of 1.25 cm² exhibit a high PCE of 6.54%. These results indicate that the PM6:IDIC blend is a promising candidate for future roll-to-roll mass manufacturing and practical application of highly efficient PSCs.
High-mobility semiconducting ultrathin films form the basis of modern electronics, and may lead to the scalable fabrication of highly performing devices. Because the ultrathin limit cannot be reached for traditional semiconductors, identifying new two-dimensional materials with both high carrier mobility and a large electronic bandgap is a pivotal goal of fundamental research. However, air-stable ultrathin semiconducting materials with superior performances remain elusive at present. Here, we report ultrathin films of non-encapsulated layered Bi2O2Se, grown by chemical vapour deposition, which demonstrate excellent air stability and high-mobility semiconducting behaviour. We observe bandgap values of ?0.8?eV, which are strongly dependent on the film thickness due to quantum-confinement effects. An ultrahigh Hall mobility value of >20,000?cm(2)?V(-1)?s(-1) is measured in as-grown Bi2O2Se nanoflakes at low temperatures. This value is comparable to what is observed in graphene grown by chemical vapour deposition and at the LaAlO3-SrTiO3 interface, making the detection of Shubnikov-de Haas quantum oscillations possible. Top-gated field-effect transistors based on Bi2O2Se crystals down to the bilayer limit exhibit high Hall mobility values (up to 450?cm(2)?V(-1)?s(-1)), large current on/off ratios (>10(6)) and near-ideal subthreshold swing values (?65?mV?dec(-1)) at room temperature. Our results make Bi2O2Se a promising candidate for future high-speed and low-power electronic applications.
Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS 2 /graphene hetero-structures by creating a device with two distinct regions containing one-layer and seven-layer MoS 2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS 2 is surprisingly higher than that in seven-layer MoS 2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS 2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS 2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS 2 /graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS 2 device.
In the past few years, ternary organic solar cells (OSCs) featuring multiple donor or acceptor materials in the active layer have emerged as a promising structure to simultaneously improve all solar cell parameters compared with traditional binary OSCs. Power conversion efficiencies around 10% have been achieved for conjugated polymers in a ternary structure, showing the great potential of ternary systems. In this review, we summarize progress in developing ternary OSCs and discuss many of the designs, chemistries and mechanisms that have been investigated. We conclude by highlighting the challenges and future directions for further development in the field of ternary blend OSCs.
Recently, power conversion efficiency (PCE) of organic solar cells has been increased up to about 10% by using solvent additive or mixed solution to elaborately adjust phase separation which is great challenge for large scale production. We report a champion PCE of 7.40% solution-processed small molecule ternary SMPV1:DIB-SQ:PC71BM solar cells by only adjusting the DIB-SQ doping ratio in donors without any treatments on the blend solutions or active layers. The champion PCE of ternary solar cells is larger than the champion PCEs sum (6.98%) of binary solar cells with SMPV1:PC71BM or DIB-SQ:PC71BM as the active layers. The PCE improvement should be attributed to the synergistic enhancement of photon harvesting, exciton dissociation, charge carrier transport and collection by appropriate DIB-SQ doping ratio in donors. The experimental results on morphology, crystalline, phase separation and charge carrier mobility of active layers well supports the PCE improvement of ternary solar cells with 10 wt% DIB-SQ doping ratio in donors.
Thiophene and its derivatives have been extensively used in organic electronics, particularly in the field of polymer solar cells (PSCs). Significant research efforts have been dedicated to modifying thiophene-based units by attaching electron-donating or withdrawing groups to tune the energy levels of conjugated materials. Herein, we report the design and synthesis of a novel thiophene derivative, FE-T, featuring a monothiophene functionalized with both an electron-withdrawing fluorine atom (F) and an ester group (E). The FE-T unit possesses distinctive advantages of both F and E groups, the synergistic effects of which enable significant downshifting of the energy levels and enhanced aggregation/crystallinity of the resulting organic materials. Shown in this work are a series of polymers obtained by incorporating the FE-T unit into a PM6 polymer to fine-tune the energetics and morphology of this high-performance PSC material. The optimal polymer in the series shows a downshifted HOMO and an improved morphology, leading to a high PCE of 16.4% with a small energy loss (0.53 eV) enabled by the reduced non-radiative energy loss (0.23 eV), which are among the best values reported for non-fullerene PSCs to date. This work shows that the FE-T unit is a promising building block to construct donor polymers for high-performance organic photovoltaic cells.
The power conversion efficiency (PCE) reaches to 12.63% or 12.19% for polymer solar cells (PSCs) based on PM6 or J71 as donor and Br-ITIC as acceptor, respectively. A series of ternary PSCs with two donors were fabricated by combining the merits of the two binary PSCs. The PM6 and J71 prefer to form alloyed donor due to the good compatibility, which is beneficial to finely optimize photon harvesting and phase separation of ternary active layers, leading to simultaneous improvement of short-circuit current density (JSC) and fill factor (FF). The improved JSC and FF can well make up for the slight loss of open-circuit voltage (VOC). The optimized ternary PSCs with 20 wt% J71 in donors achieve a PCE of 14.13% and a FF of 78.4%. More than 11% PCE improvement is achieved by adopting ternary strategy on the basis of two binary PSCs with PCE over 12%, also keeping simple fabrication technology.
Morphology of the donor:acceptor blend plays a critical role in the photovoltaic performance of the organic solar cells (OSCs). Herein, liquid-phase-exfoliated black phosphorus nanoflakes (BPNFs), for their outstanding electronic property and good compatibility to solution process, were applied to fullerene-free OSCs as morphology modifier. Revealed by X-ray scattering measurements, the PTB7-Th:IEICO-4F blends incorporated with BPNFs exhibit more ordered π-π stacking and promoted domain purity, contributing to lower charge transport resistance and suppressed charge recombination within the bulk heterojunction (BHJ). As a result, a high fill factor (FF) of 0.73 and a best power conversion efficiency (PCE) of 12.2% were obtained for fullerene-free OSCs based on PTB7-Th:IEICO-4F blends incorporating with BPNFs, which is among the highest FF of the as-cast fullerene-free OSCs with PCE over 12%. More importantly, the embedded BPNFs help to improve the morphological stability of the devices probably by retarding the phase mixing in the BHJ during the aging period. Besides, analogous enhancements were observed in another fullerene-free OSCs based on PBDB-T:ITIC. In a word, this work provides a new strategy of using two-dimentional nanoflakes as facile and universal morphology modifier for efficient fullerene-free OSCs.
A diketopyrrolopyrrole-based small bandgap polymer (DPPT-TT) with high-mobility is introduced as an additive to D-A1-D-A2 type thieno[3,4-b]thiophene-based random copolymer (P3):(6,6)-phenyl-C70-butyric acid methyl ester (PC71BM) polymer solar cells (PSCs). The average power conversion efficiencies (PCEs) were improved from 6.15% to 8.30% with the addition of 0.5% DPPT-TT. The photocurrent density versus effective voltage (Jph-Veff) curves, short-circuit current density (JSC) and open ciruit voltage (VOC) as a function of incident light intensity, photoluminescence (PL) and time-resolved transient PL (TRTPL) spectra were investigated, and the results certified the effect of DPPT-TT as the third component material in terms of efficient exciton dissociation and weakened charge carrier recombination. The relationship of VOC and weight ratio of DPPT-TT was explained with density functional theory (DFT) calculations and electron density of state of unit mass (Ne), indicating the formation of a polymer alloy in ternary blend. With proper addition of DPPT-TT, the mobility of electron and hole become more balanced and the efficiency of exciton utilization is improved due to the existence of Förster resonance energy transfer (FRET), which also contributes to the enhanced JSC and PCEs. Our work demonstrates that appropriate donor polymers form polymer alloy in blend is a rational strategy to improve photovoltaic performance.
Though organic photovoltaic cells (OPVs) have many advantages, their performance still lags far behind that of other photovoltaic platforms. One of the most fundamental reasons for this is the low charge mobility of organic materials, leading to a limit on the active layer thickness and efficient light absorption. In this work, guided by a semi-empirical model analysis and using the tandem cell strategy to overcome such issues, and taking advantage of the high diversity and easily tunable band structure of organic
materials, a record and certified 17.29% power conversion efficiency for a 2-terminal monolithic solution processed tandem OPV is achieved.
The ordered aggregation of non-fullerene small molecular acceptors (SMAs) plays a key role in determining the charge transport and bimolecular recombination in polymer/SMAs solar cells. However, due to the asymmetric phase separation in many polymer/SMAs systems, the polymers are prone to form network first, which inhibits the molecular diffusion of SMAs, resulting in weak crystallinity of SMAs. Here, we demonstrate a sequent-crystallization method for high performance PBDB-T/ITIC solar cell with much improved crystallinity of ITIC. By tuning the sequence of thermal annealing (TA) and solvent vapor annealing (SVA), sequent-crystallization of ITIC and PBDB-T can be fine controlled to grow high crystalline ITIC and PBDB-T network. The crystallization kinetics results indicate that when the crystallization of ITIC occurred prior to the formation of the PBDB-T crystallized network, the crystallinity of ITIC is significantly improved due to high molecular diffusion. However, if the crystallization of PBDB-T occurred first, the diffusion of ITIC was restricted by the crystalline network of PBDB-T, resulting in a low crystallinity of ITIC. The enhanced crystallinity of ITIC is beneficial to the electron transport and suppressed the bimolecular recombination, which helps boost device performance from 8.14% to 10.95%. This work demonstrates that manipulation of crystallization sequence of donor and acceptor may be a key to further boost the efficiency of polymer/SMAs solar cells.
Non-fullerene polymer solar cells (PSCs) attract more attention due to the constantly refreshed power conversion efficiency (PCE) based on the versatile non-fullerene acceptors. In this work, the PCEs of 10.51% and 11.02% are obtained for the two kinds of non-fullerene PSCs with IDT6CN-M or ITCPTC as acceptor and PBDB-T as donor, respectively. ITCPTC has relatively narrow bandgap and high absorption coefficient compared with IDT6CN-M, which well explains the relatively large short-circuit current density of 17.44 mA/cm2 for ITCPTC based binary PSCs. Meanwhile, IDT6CN-M based binary PSCs exhibit the relatively high fill factor (FF) of 75.3% and open-circuit voltage of 0.915 V. The PCE of 11.92% and FF of 76.5% are achieved for the ternary PSCs with 60 wt% ITCPTC content in acceptors, which should be attributed to the enhanced photon harvesting and their good compatibility for synergistic improvement of exciton utilization and charge transport in the ternary active layers. The FF of 76.5% should be the top value of ternary non-fullerene PSCs.
In this work, highly efficient ternary-blend organic solar cells (TB-OSCs) are reported based on a low-bandgap copolymer of PTB7-Th, a medium-bandgap copolymer of PBDB-T, and a wide-bandgap small molecule of SFBRCN. The ternary-blend layer exhibits a good complementary absorption in the range of 300-800 nm, in which PTB7-Th and PBDB-T have excellent miscibility with each other and a desirable phase separation with SFBRCN. In such devices, there exist multiple energy transfer pathways from PBDB-T to PTB7-Th, and from SFBRCN to the above two polymer donors. The hole-back transfer from PTB7-Th to PBDB-T and multiple electron transfers between the acceptor and the donor materials are also observed for elevating the whole device performance. After systematically optimizing the weight ratio of PBDB-T:PTB7-Th:SFBRCN, a champion power conversion efficiency (PCE) of 12.27% is finally achieved with an open-circuit voltage (Voc ) of 0.93 V, a short-circuit current density (Jsc ) of 17.86 mA cm(-2) , and a fill factor of 73.9%, which is the highest value for the ternary OSCs reported so far. Importantly, the TB-OSCs exhibit a broad composition tolerance with a high PCE over 10% throughout the whole blend ratios.
Each component layer in a perovskite solar cell plays an important role in the cell performance. Here, a few types of polymers including representative p-type and n-type semiconductors, and a classical insulator, are chosen to dope into a perovskite film. The long-chain polymer helps to form a network among the perovskite crystalline grains, as witnessed by the improved film morphology and device stability. The dewetting process is greatly suppressed by the cross-linking effect of the polymer chains, thereby resulting in uniform perovskite films with large grain sizes. Moreover, it is found that the polymer-doped perovskite shows a reduced trap-state density, likely due to the polymer effectively passivating the perovskite grain surface. Meanwhile the doped polymer formed a bridge between grains for efficient charge transport. Using this approach, the solar cell efficiency is improved from 17.43% to as high as 19.19%, with a much improved stability. As it is not required for the polymer to have a strict energy level matching with the perovskite, in principle, one may use a variety of polymers for this type of device design.
Although organic photovoltaics (OPVs) have been investigated for more than 2 decades, the power conversion efficiencies of OPVs are much lower than those of inorganic or perovskite solar cells. One effective approach to improve the efficiency of OPVs is to introduce additives to enhance light harvesting as well as charge transportation in the devices. Here, black phosphorus quantum dots (BPQDs) are introduced in OPVs as an additive for the first time. By adding BPQDs with the weight percentage of only 0.055 % relative to polymer donors in the OPVs, the device efficiencies can be dramatically improved for more than 10%. It is worth noting that the weight percentage is much lower than those of any other additives used in OPVs before, which is mainly due to the 2-dimentional nature as well as the strong broadband light absorption and scattering of the BPQDs. This work paves a way for using 2-dimentional quantum dots in OPVs as a cost-effective approach to enhance device efficiencies.
In this paper, we demonstrated the enhancement in power conversion efficency (PCE) of solar cells based on Poly(3-hexylthiophene-2,5-diyl) (P3HT): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) by incorporation of functionalized 2D-MoS2 NS as an additional charge transporting material. The enhancement in PCE of ternary solar cells arises due to the synergic enhancement in exciton dissociation and improvement in both electrons and holes transport through the active layer of the solar cells. The improved hole mobility is attributed to the formation of long range ordered nano fibrillar structure of polymer phases and improved crystallinity in the presence of 2D-MoS2 NS. The improved electron mobility arises due to the highly conducting 2D network of MoS2 NS which provides additional electron transport channels within the active layer. The nanosheets incorporated ternary blend solar cells exhibited 32 % enhancement in PCE relative to the binary blend P3HT:PC71BM.
The development of large-scale production methods of two-dimensional (2D) crystals, with on-demand control of the area and thickness, is mandatory to fulfill the potential applications of such nanomaterials for photovoltaics. Inverted bulk heterojunction (BHJ) organic solar cell (OSC), that exploits a polymer-fullerene binary blend as the active material, is one potentially important application area for 2D crystals. A large ongoing effort is indeed currently devoted to the introduction of 2D crystals in the binary blend to improve the charge transport properties. While it is expected that the nanoscale domain sizes of the different components of the blend will significantly impact the performance of the OSC, to date, there is no evidence of quantitative information of the interplay between 2D crystals and fullerene domain sizes. Here, we demonstrate that by matching the size of WSe2 few-layer 2D crystals, produced by liquid phase exfoliation methods, with that of the PC71BM fullerene domain in BHJ OSCs we obtain power conversion efficiencies (PCE) of ~9.3%, reaching a 15% improvement with respect to standard binary devices (PCE=8.10%), i.e., without the addition of WSe2 flakes. This is the highest ever reported PCE for 2D materials-based OSCs, obtained thanks to the enhanced exciton generation and exciton dissociation at the WSe2-fullerene interface and also electron extraction to the back metal contact as a consequence of a balanced charge carriers mobility. These results pave the way toward the implementation of transition metal di-chalcogenides to boost the performance of BHJ OSCs.
Aimed at achieving ideal morphology, illuminating morphology–performance relationship, and further improving the power conversion efficiency (PCE) of ternary polymer solar cells (TSCs), a ternary system is designed based on PTB7-Th:PffBT4T-2OD:PC71BM in this work. The PffBT4T-2OD owns large absorption cross section, proper energy levels, and good crystallinity, which enhances exciton generation, charge dissociation and transport and suppresses charge recombination, thus remarkably increasing the short-circuit current density (Jsc) and fill factor (FF). Finally, a notable PCE of 10.72% is obtained for the TSCs with 15% weight ratio of PffBT4T-2OD. As for the working mechanism, it confirmed the energy transfer from PffBT4T-2OD to PTB7-Th, which contributes to the improved exciton generation. And morphology characterization indicates that the devices with 15% PffBT4T-2OD possess both appropriate domain size (25 nm) and enhanced domain purity. Under this condition, it affords numerous D/A interface for exciton dissociation and good bicontinuous nanostructure for charge transport simultaneously. As a result, the device with 15% PffBT4T-2OD exhibits improved exciton generation, enhanced charge dissociation possibility, elevated hole mobility and inhibited charge recombination, leading to elevated Jsc (19.02 mA cm−2) and FF (72.62%) simultaneously. This work indicates that morphology optimization as well as energy transfer plays a significant role in improving TSC performance.
The development of thick organic photovoltaics (OPV) could increase absorption in the active layer and ease manufacturing constraints in large-scale solar panel production. However, the efficiencies of most low-bandgap OPVs decrease substantially when the active layers exceed ~ 100 nm (due to low crystallinity and short exciton diffusion length). Herein, we report the use of solvent additive diphenyl ether (DPE) that facilitates the fabrication of thick (180 nm) active layers and triples the power conversion efficiency (PCE) of conventional thienothiophene-co-benzodithiophene polymer (PTB7)-based OPVs from 1.75% to 6.19%. These results demonstrate a 20% higher PCE than conventional (PTB7)-based OPV devices using 1,8-diiodooctane (DIO). Morphology studies reveal that DPE promotes the formation of nano-fibrilla networks and ordered packing of PTB7 in the active layer that facilitate charge transport over longer distances. We further demonstrate that DPE improves the fill factor and photocurrent collection by enhancing the overall optical absorption, reducing the series resistance, and suppressing bimolecular recombination.
A nonfullerene-based polymer solar cell (PSC) which significantly outperforms fullerene-based PSCs with respect to the power-conversion efficiency is demonstrated for the first time. An efficiency >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB-T and ITIC as donor and acceptor, respectively.
The pure tetragonal bismuth oxiselenide nanosheets are synthesized by the composite-molten-salt approach at 200 °C. Field emission scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy are used to characterize the structure, morphology, and composition of the sample. The results show that the thickness of the nanosheets is about 120 nm. The sample for thermoelectric property measurements is prepared using cold pressing method. Thermoelectric properties, including electrical conductivity, Seebeck coefficient and thermal conductivity, are measured from room temperature to 470 K. The results show that the sample exhibits n-type semiconductor behavior with low thermal conductivity (κ300 = 0.346 Wm−1 K−1, and κ470 = 0.458 Wm−1 K−1). Although the obtained figure of merit is small, it would be enhanced with increase in temperature.
At present, state-of-the-art single-junction organic photovoltaic devices have power conversion efficiencies of >9% and >8% for polymer- and small-molecule-based devices, respectively. Here, we report a solution-processed organic photovoltaic device based on DRCN7T, which employs an oligothiophene-like small molecule with seven conjugation units as the backbone and 2-(1,1-dicyanomethylene)rhodanine as the terminal unit. With [6,6]-phenyl C-71-butyric acid methyl ester (PC71BM) as the acceptor, an optimized power conversion efficiency of 9.30% (certified at 8.995%) is achieved. The DRCN7T-based devices have a nearly 100% internal quantum efficiency, which we believe is due to an optimized nanoscale interpenetrating donor/acceptor network (with highly crystalline donor fibrils with diameters of similar to 10 nm, close to the exciton diffusion length in organic materials) and the use of an efficient electron transport layer.
Organic–inorganic hybrid solar cells were expected to adopt the advantages of both organic and inorganic materials. Due to several crucial problems, the power conversion efficiency of most hybrid solar cells was lower than 1%. Recent work reported the highest power conversion efficiency of a hybrid solar cell as 11.3%, which increased the research interest into organic–inorganic hybrid solar cells. This article focuses on the progress in state-of-the-art research on organic–inorganic hybrid solar cells and the associated key issues, including the energy band alignment of the organic and inorganic components, interface control of the heterojunction, and the use of ordered nanostructures were discussed. The challenges and prospects for organic–inorganic hybrid solar cells in the near future are discussed.
The current–voltage characteristics of methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM)-based devices are investigated as a function of temperature. The occurrence of space–charge limited current enables a direct determination of the electron mobility. At room temperature, an electron mobility of μe = 2 × 10–7 m2 V–1 s–1 has been obtained. This electron mobility is more than three orders of magnitude larger than the hole mobility of donor-type conjugated polymer poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-p-phenylene vinylene) (OC1C10-PPV). As a result, the dark current in PCBM/OC1C10-PPV based devices is completely dominated by electrons. The observed field and temperature-dependence of the electron mobility of PCBM can be described with a Gaussian disorder model. This provides information about the energetic disorder and average transport-site separation in PCBM.
In spite of the rapid increase in the power conversion efficiency (PCE) of polymer solar cells (PSCs), the poor stability of the photoactive layer in air under sunlight is a critical problem blocking commercialization of PSCs. This study investigates the photo-oxidation behavior of a bulk-heterojunction (BHJ) photoactive film made of single-crystalline poly(3-hexlythiophene) (P3HT) nanofibrils and fullerene derivatives [phenyl-C61-butyric methyl ester (PCBM), indene-C 60 bisadduct (ICBA)]. Because the single-crystalline P3HT nanofibrils had tightly packed - stacking, the permeation of oxygen and water into the nanofibrils was significantly reduced. Chemical changes in P3HT were not apparent in the nanofibrils, and hence the air stability of the nanofibril-based BHJ film was considerably enhanced as compared with conventional BHJ films. The chemical changes were monitored by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and UV-vis absorbance. Inverted PSCs made of the nanofibril-based BHJ layer also showed significantly enhanced air stability under sunlight. The nanofibril-based solar cell maintained more than 80% of its initial PCE after 30 days of continuous exposure to sunlight (AM 1.5G, 100 mW/cm2), whereas the PCE of the conventional BHJ solar cell decreased to 20% of its initial PCE under the same experimental conditions.
Polymeric organic photovoltaic (OPV) cells are promising candidates for low-cost, high-performance energy sources due to their low material and processing costs, flexibility, and ease of manufacturing by solution processes. However, low power-conversion efficiency (PCE) has impeded the development of OPV cells. The low PCE in OPV solar cells has been attributed to low carrier mobility, which is related to the transport length of the charge carriers within active layers. Graphene can be an ideal material for assisting the charge transport in the active layer of OPV cells due to its excellent charger carrier mobility, thermal and chemical stability, and compatibility with the solution process. In this work, we demonstrated for the first time an improvement of the PCE (up to 40%) in OPV bulk-heterojunction (BHJ) cells by incorporating charge-selective graphene flakes into the BHJ active layer. The charge selectivity of graphene flakes was achieved by nitrogen doping (N-doped graphene). The N-doped graphene, when mixed in the active layer (N-doped graphene/polymer: fullerene composites), provided transport pathways exclusively to specific charge carriers through the modulation of band-gap structures. We discuss further the enhancement of the PCE in OPV cells with respect to charge-carrier mobility.
As a conceptually new class of two dimensional (2D) materials, the ultrathin nanosheets as inorganic graphene analogues (IGAs) play an increasingly vital role in the new-generation electronics. However, the relatively low electrical conductivity of inorganic ultrathin nanosheets in current stage significantly hampered their conducting electrode applications in constructing nanodevices. We developed the unprecedentedly high electrical conductivity in inorganic ultrathin nanosheets. The hydric titanium disulfide (HTS) ultrathin nanosheets, as a new IGAs, exhibit the exclusively high electrical conductivity of 6.76×104 S/m at room temperature, which is superior to indium tin oxide (ITO, 1.9×104 S/m), recording the best value in the solution assembled 2D thin films of both graphene (5.5×104 S/m) and inorganic graphene analogues (5.0×102 S/m). The modified hydrogen on S-Ti-S layers contributes additional electrons to the TiS2 layered frameworks, rendering the controllable electrical conductivity as well as the electron concentrations. Together with synergic advantages of the excellent mechanical flexibility, high stability and stamp-transferrable properties, the HTS thin films show promising capability for being the next generation conducting electrode material in the nanodevice fields.
The high-yield fabrication of tetrapodal CdSe, CdTe, and CdSexTe1-x nanocrystals is systematically studied. CdSe nanocrystals are prepared by first controlling the synthesis of high-quality wurtzite CdSe and zinc blende CdSe nanocrystals at a relatively high temperature (260 degrees C) by selecting different ligands. Then, based on the phase control of the CdSe nanocrystals, two nanoparticle-tailoring routes (i.e., a seed-epitaxial route and ligand-dependent multi-injecting route) are used, and a high yield of CdSe tetrapods is obtained. CdTe nanocrystals are prepared by adjusting the ligand composition and the ratio of Cd to Te; CdTe tetrapods are synthesized in high yield using a mixed ligand that does not contain alkylphosphonic acids. Moreover, the nanoscale Te powder (Te nanowires/nanorods), which is highly soluble in the ligand solvent, is first used as a Te source to synthesize CdTe nanocrystals, which remarkably enhanced the output of the CdTe nanocrystals in one reaction. Furthermore, composition-tunable ternary CdSexTe1-x alloyed tetrapods are synthesized on a large scale, for the first time, by thermolyzing the mixture of the organometallic Cd precursor and the mixed (Se + Te) source in a mixed-ligand solution. The CdSe, CdTe, and CdSexTe1-x nanocrystals are characterized by transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, X-ray diffraction, and UV-vis and photoluminescence (PL) spectroscopy. Interesting nonlinear, composition-dependent absorption and PL spectra are observed for the ternary CdSexTe1-x alloyed nanocrystals. The band-edge positions of the nanocrystals of CdSe, CdSexTe1-x, and CdTe are systematically studied by cyclic voltammetry.
We demonstrate here that the nanostructure of poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction (BHJ) can be tuned by inorganic nanoparticles (INPs) for enhanced solar cell performance. The self-organized nanostructural evolution of P3HT/PCBM/INPs thin films was investigated by using simultaneous grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide-angle X-ray scattering (GIWAXS) technique. Including INPs into P3HT/PCBM leads to (1) diffusion of PCBM molecules into aggregated PCBM clusters and (2) formation of interpenetrating networks that contain INPs which interact with amorphous P3HT polymer chains that are intercalated with PCBM molecules. Both of the nanostructures provide efficient pathways for free electron transport. The distinctive INP-tuned nanostructures are thermally stable and exhibit significantly enhanced electron mobility, external quantum efficiency, and photovoltaic device performance. These gains over conventional P3HT/PCBM directly result from newly demonstrated nanostructure. This work provides an attractive strategy for manipulating the phase-separated BHJ layers and also increases insight into nanostructural evolution when INPs are incorporated into BHJs.
Golden solar cells: Several positive effects arise from the addition of truncated octahedral Au nanoparticles (ca.70nm diameter) to bulk heterojunction (BHJ) photovoltaic cells fabricated from a variety of donor polymers and PC 70BM as acceptor (see picture). At the optimized blend ratio of Au nanoparticles (5wt%) in the active layer, the power conversion efficiency increased for all polymer/PC70BM systems under study.