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Single material organic solar cells (SMOSCs) are based on ambivalent materials containing electron donor (D) and acceptor (A) units capable to ensure the basic functions of light absorption, exciton dissociation, and charge transport. Compared to bicomponent bulk heterojunctions, SMOSCs present several major advantages such as considerable simplifi...
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Thanks to the development of acceptor–donor–acceptor (A–D–A) type electron acceptors, organic solar cells (OSCs) have achieved marvelous progress in recent years. However, a systematic investigation about the structure–efficiency relationship is still highly desired to better understand the working mechanisms inside a bulk heterojunction (BHJ). In...
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... 9,10 Recently, several works have shown that free charges can also be generated spontaneously in single-component organic materials. [11][12][13][14] This means that excitons no longer need to migrate to the donor-acceptor interface to dissociate. To explain the reasons behind this, different mechanisms have been proposed such as local nonuniform fields, 5,15 delocalization of excitons [i.e., hot excitons (HEs)], [16][17][18] polarization effect, 19 entropy gain, and disorder effects. ...
Ultrafast pump-push-probe/photocurrent experiments have confirmed that free charges can be spontaneously generated in single-component organic solar cells. A deeper understanding of the experimental results is expected to further modulate the charge yield. Herein, the effect of an infrared push pulse on the relaxed exciton in conjugated polymers is theoretically studied. We find that the relaxed exciton can be pushed into different hot excitons depending on the energy of this infrared pulse. In particular, the dynamics of the transition from localized to delocalized excitons is explicitly presented. Moreover, we attempt to demonstrate that the delocalization effect of hot exciton is favorable for charge generation by introducing a driving field. The results suggest that the strength of the driving field and timescale required for the dissociation of hot exciton is significantly reduced compared to this relaxed exciton. Finally, the influence of the photoexcitation conditions on the charge generation is discussed to further elucidate the effect of hot exciton delocalization. Overall, this work has the potential to provide further information for the analysis and control of charge generation by hot exciton dissociation.
... This is a clear evidence that the most of excitons occurs at ZnO-NP:PBDB-T interface, which has been observed in previous work. [43,44,45,46,47] Moreover, the device performance drop to 0.02% with the conventional device structure. These results suggest that photon-generated excitons in 6TIC-4F are spontaneously dissociated into free carriers, rather than taking any heterojunction interface for exiton dissociation. ...
Comprehensive Summary
Since 1986, the donor‐acceptor (D:A) heterojunction has been regarded a necessity for high‐efficiency organic photovoltaics (OPVs), due to its unique advantage in compensating the intrinsic limitations of organic semiconductors, such as high exciton binding energy and poor ambipolar charge mobility. While this adversely causes tremendous non‐radiative charge recombination and instability issues, which currently become the most critical limits for commercialization of OPVs. Here, we present a concept‐to‐proof study on the potential of D:A heterojunction free OPV by taking advantage of recent progress of non‐fullerene acceptors. First, we demonstrate that the “free carriers” can be spontaneously generated upon illumination in an NFA, i.e. the 6TIC‐4F single layer. Second, the 6TIC‐4F layer also exhibits good ambipolar charge transporting property. These exceptional characteristics distinguish it from the traditional organic semiconductors, and relieve it from the reliance of D:A heterojunction to independently work as active layer. As a result, the subsequent OPV by simply sandwiching the 6TIC‐4F layer between the cathode and anode yields a considerably high power conversion efficiency ~ 1%. Moreover, we find the D:A heterojunction free device exhibits two order of magnitude higher electroluminescence quantum efficiency and significantly reduced V OC loss by 0.16 eV compared to those of the D:A BHJ structure, validating its promise for higher efficiency in the future. Therefore, our work demonstrates the possibility of using D:A heterojunction‐free device structure for high performance, that can potentially become the next game changer of OPV.
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... Instead, random terpolymerization that combines three units in the polymer backbone can have a good impact on light absorption profiles while also having a significant chance of enhancing PCEs. Thus, this integration is highly beneficial for charge separation due to the process from sunlight absorption, exciton generation to dissociation of electrons and holes that may happen in the same molecule which can handle the trouble about the short diffusion length of excitons in OSCs [16][17][18]. In addition, random conjugated terpolymers provide a simple but efficient synthetic strategy for high-performance OSCs [19][20][21][22][23]. ...
Herein, we designed and synthesized two novel donor-acceptor1-acceptor2-acceptor1 (D-A1-A2-A1) type random conjugated terpolymers, DTP-TPD-DPP and DTP-TPD-BT, as a donor component for single-junction non-fullerene organic solar cells. The terpolymers were randomly combined from N-aryldithienopyrrole (DTP) donor unit and N-alkylthienopyrroledione (TPD) acceptor unit with electron-accepting dibrominated acceptor units including diketopyrrolopyrrole (DPP) or bithiophenebenzothiadiazole (TBT) by direct arylation polycondensation. Compared to two different acceptor units in the polymer backbone, DTP-TPD-DPP containing DPP exhibits stronger intramolecular charge transfer. Thus, the single-layer organic solar cells based on DTP-TPD-DPP:ITIC (1:1) demonstrated a power conversion efficiency (PCE) of 2.92 % and a high open-circuit voltage Voc of 1.0 V while devices using DTP-TPD-BT obtained a PCE of 2.64 % under the same condition fabrication in the ambient condition without any additives. The results showed that random conjugated terpolymer is an efficient and straightforward synthetic strategy to explore promising donor materials for high-performance single-junction organic solar cells.
... The optical properties of the molecules synthesized were investigated by UV-vis absorption spectroscopy in diluted CHCl 3 solutions (10 −6 M) and thin films (Figure 2a and Table 1). The compounds showed rather similar shapes of the absorption spectra: the bands at the high-energy region (300-420 nm) usually ascribed to π-π* transitions and the intensive bands at 620-840 nm usually ascribed to the ICT [40,41] or with a mixed character [42]. BTPT-4F-OD has red-shifted absorption spectra as compared to BTPT-OD due to a narrower electrochemical bandgap as discussed below. ...
The development of novel non-fullerene small-molecule acceptors (NFAs) with a simple chemical structure for high-performance organic solar cells (OSCs) remains an urgent research challenge to enable their upscaling and commercialization. In this work, we report on the synthesis and comprehensive investigation of two new acceptor molecules (BTPT-OD and BTPT-4F-OD), which have one of the simplest fused structures among the Y series of NFAs, along with the medium energy bandgap (1.85 eV–1.94 eV) and strong absorption in the visible and near-IR spectral range (700–950 nm). The novel NFAs have high thermal stability, good solubility combined with a high degree of crystallinity, and deep-lying levels of the lowest unoccupied molecular orbital (up to −3.94 eV). The BTPT-OD with indan-1-one-3-dicyanvinyl terminal acceptor group is superior to its counterpart BTPT-4F-OD with 5,6-difluorindan-1-one-3-dicyanvinyl group both in the number of synthetic steps and in the photovoltaic performance in OSCs. PM6:BTPT-OD systems exhibit superior photovoltaic performance due to the higher charge mobility and degree of photoresponsiveness, faster carrier extraction, and longer carrier lifetime. As a result, BTPT-OD has almost two times higher photovoltaic performance with PM6 as a donor material due to the higher JSC and FF than BTPT-4F-OD systems. The results obtained indicate that further development of OSCs can be well achieved through a rational molecular design.
... It is, therefore, desirable to target OPVs with a single-material active layer. 105 However, organic small molecules and polymers on their own do not possess the high levels of charge photogeneration 106 or long charge carrier lifetimes required. 107 Indeed, while many pristine organic materials can generate charge carriers, these typically recombine on ultrafast timescales due to their inability to escape their mutual Coulombic attraction. ...
Organic photovoltaics are remarkably close to reaching a landmark power conversion efficiency of 20%. Given the current urgent concerns regarding climate change, research into renewable energy solutions is crucially important. In this perspective article, we highlight several key aspects of organic photovoltaics, ranging from fundamental understanding to implementation, that need to be addressed to ensure the success of this promising technology. We cover the intriguing ability of some acceptors to undergo efficient charge photogeneration in the absence of an energetic driving force and the effects of the resulting state hybridization. We explore one of the primary loss mechanisms of organic photovoltaics—non-radiative voltage losses—and the influence of the energy gap law. Triplet states are becoming increasingly relevant owing to their presence in even the most efficient non-fullerene blends, and we assess their role as both a loss mechanism and a potential strategy to enhance efficiency. Finally, two ways in which the implementation of organic photovoltaics can be simplified are addressed. The standard bulk heterojunction architecture could be superseded by either single material photovoltaics or sequentially deposited heterojunctions, and the attributes of both are considered. While several important challenges still lie ahead for organic photovoltaics, their future is, indeed, bright.
... Following the first path, a single donor-acceptor material with a narrow absorption spectrum and effective charge photogeneration seems to be feasible. Recently, much attention has been paid to single-component solar cells based on donor-acceptor materials [15,16]. At the same time, modification of the architecture of the device to optimize its spectral response [14]. ...
... Following the first path, a single donor-acceptor material with a narrow absorption spectrum and effective charge photogeneration seems to be feasible. Recently, much attention has been paid to single-component solar cells based on donor-acceptor materials [15,16]. At the same time, single-component organic photodetectors have far less studied, as follows from articles [17][18][19][20][21][22][23][24]. ...
Photodetectors based on organic materials are attractive due to their tunable spectral response and biocompatibility, meaning that they are a promising platform for an artificial human eye. To mimic the photoelectric response of the human eye, narrowband spectrally-selective organic photodetectors are in great demand, and single-component organic photodetectors based on donor-acceptor conjugated molecules are a noteworthy candidate. In this work, we present single-component selective full-color organic photodetectors based on donor-acceptor conjugated molecules synthetized to mimic the spectral response of the cones and rods of a human eye. The photodetectors demonstrated a high responsivity (up to 70 mA/W) with a response time of less than 1 µs, which is three orders of magnitude faster than that of human eye photoreceptors. Our results demonstrate the possibility of the creation of an artificial eye or photoactive eye “prostheses”.
... Charge generation in most OPVs is realised using band offsets as the driving force in donor-acceptor materials 18 . However, a 'spontaneous' exciton dissociation is also possible and has recently found applications in single component organic solar cells 19,20 , where the molecules of the same type act as both donor and acceptor. Using single-component material reduces the negative effect of exciton diffusion and excess energy loss on the open-circuit voltage of organic photovoltaic devices 21,22 . ...
Fundamental mechanisms underlying exciton formation in organic semiconductors are complex and elusive as it occurs on ultrashort sub-100-fs timescales. Some fundamental aspects of this process, such as the evolution of exciton binding energy, have not been resolved in time experimentally. Here, we apply a combination of sub-10-fs Pump-Push-Photocurrent, Pump-Push-Photoluminescence, and Pump-Probe spectroscopies to polyfluorene devices to track the ultrafast formation of excitons. While Pump-Probe is sensitive to the total concentration of excited states, Pump-Push-Photocurrent and Pump-Push-Photoluminescence are sensitive to bound states only, providing access to exciton binding dynamics. We find that excitons created by near-absorption-edge photons are intrinsically bound states, or become such within 10 fs after excitation. Meanwhile, excitons with a modest >0.3 eV excess energy can dissociate spontaneously within 50 fs before acquiring bound character. These conclusions are supported by excited-state molecular dynamics simulations and a global kinetic model which quantitatively reproduce experimental data.
... In the past few decades, many SCOSCs based on different single-component materials have been reported. 10 In these devices, fullerenes or nonfullerenes were employed as the electron-acceptor units in the singlecomponent active materials. 11−20 For example, Pierini et al. ...
... To address the above-mentioned difficulties in industrial application, employing single-component materials (SCMs) is an elegant approach, which contain chemically connected donor (D) moieties and acceptor (A) moieties within one material and could realize photoelectric conversion by themselves. 16,17 This feature renders simplified ink design processing and recycling since only one material is involved. Most importantly, the covalent-bonded structure overcomes the poor miscibility in some donor and acceptor systems for a proper phase-separated morphology [18][19][20] and meanwhile suppresses the gradual demixing between the donor and the acceptor, providing a stabilized nanophase morphology for long-term stability. ...
... 21 It has been generally regarded that using SCM is an effective and generic approach for achieving a higher stability than that exhibited by the corresponding BHJ. 17 In our previous study, we have demonstrated that single-component OSCs (SCOSCs) based on a double-cable polymer are stable even under harsh conditions, such as baking at 160 C or continuous illumination at 90 C, suggesting them as promising photovoltaic materials for potential applications under harsh conditions. 21 There have been several soaring stages periodically in the development of OSCs when observing the evolution of the record efficiency of BHJ systems, which is shown in Figure 1. ...
... As schematically shown in Figure 1, side-chain polymers and molecular dyads and triads belong to the BHJ model due to the inter-domain charge generation process, whereas in-chain polymers and homojunction molecules possibly exhibit intra-chain direct photogeneration of charge carriers as a homojunction model. 16,17,27,28 Throughout the early stages, SCMs exhibited similar performance, starting from the efficiency of around 0.5% before 2009 and then staggering around 2%-3% until 2017. 16,[29][30][31] Nevertheless, tedious developments resulted in PCEs up to 5.34% for molecular dyads, 32,33 2.9% for homojunction molecules, 34 8.40% for side-chain polymers, 23 and the most recent performance breakthrough of 11.32% for in-chain (or di-block co) polymers. ...
Although the power conversion efficiencies (PCEs) of bulk heterojunction (BHJ) organic solar cells (OSCs) continue increasing toward the 20% milestone, important factors for industrial application are mostly neglected, such as photostability and cost potential. Single-component OSCs (SCOSCs) employing materials with chemically bonded donor and acceptor moieties successfully overcome the immiscibility between the donor and the acceptor as well as the resultant self-aggregation under external stress. To inspire a broader interest, the industrial figure of merit (i-FoM) of BHJ OSCs and the corresponding SCOSCs is calculated and analyzed, which includes PCE, photostability, and synthetic complexity (SC) index. Despite having a slightly more complex synthesis, all SCOSCs exhibit increased i-FoM values compared with the corresponding BHJ OSCs, and with the increase in efficiency, SCOSCs possess further potential for a higher i-FoM value. With the excellent photostability of nearly all investigated single-component semiconductors, SCOSCs are coming into the focus of attention for industrial utilization.
... However, these dyads always showed poor photovoltaic performance with PCEs below 2% because of the unbalanced content of D/A part with narrow absorption spectrum and disadvantaged morphology [336]. Afterwards, electron-deficient units like diketopyrrolopyrrole, benzothiadiazole and rhodanine and electron-donating units such as benzodithiophene, dithiafulvalene and fluorene were introduced into the molecular dyads to broaden the photoabsorption region and to tune the energy level and crystallinity of the donor part, and PCEs of the SCOSCs fabricated by these molecule dyads were optimized to 4.26% [338,339]. PDI is an electron-deficient conjugated unit with high crystallinity and commonly used to build electron acceptors in organic solar cells, so as to the molecular dyads for SCOSCs. In 2009, Geng et al. [340] used oligo(fluorene-alt-biothiophene)s with liquid crystal properties as donor segment, PDI units as the acceptor part and synthesized a series of linear molecular dyads with different molecular length, as shown in Figure 24. ...
During past several years, the photovoltaic performances of organic solar cells (OSCs) have achieved rapid progress with power conversion efficiencies (PCEs) over 18%, demonstrating a great practical application prospect. The development of material science including conjugated polymer donors, oligomer-like organic molecule donors, fused and nonfused ring acceptors, polymer acceptors, single-component organic solar cells and water/alcohol soluble interface materials are the key research topics in OSC field. Herein, the recent progress of these aspects is systematically summarized. Meanwhile, the current problems and future development are also discussed.
