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Defects passivation by Lewis acid or Lewis base. a Diagram depicting the formation of a dative covalent bond between two atoms. b Diagram of the passivation of trap states. 137 c, d Chemical structures of reported small organic molecules for passivation of perovskite films: c Lewis acid: IPFB (iodopentafluorobenzene) 103 and F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane). 104 d Lewis base: thiophene, pyridine, 65 TEA (tetra-ethyl ammonium), 114 BA (benzylamine), 66 EDT (1,2-ethanedithiol). 106 e Images of unmodified FAPbI 3 , AFAPbI 3 , BA-FAPbI 3 , and PA-FAPbI 3 films after 4 months' exposure under 50 ? 5 RH% air. 66 f Internal PLQE measurements over time under illumination in dry N 2 , dry air, and humid air. Inset: Time-resolved PL decays of the films after the stated treatment with pulsed excitation at 405 nm. 121
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Metal halide perovskites have achieved great success in photovoltaic applications during the last few years. The solar to electrical power conversion efficiency (PCE) of perovskite solar cells has been rapidly improved from 3.9% to certified 22.7% due to the extensive efforts on film deposition methods, composition and device engineering. Further i...
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... of the charge transport layers. In this section, we will mainly focus on the passivation of perovskite by small molecules. The principle for choosing efficient passivation molecules is mainly based on "Lewis acid-Lewis base coordination". The chemical structures of the used small molecules and the related device performance are summarized in Fig. 4 and Table ...
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... of small molecules on perovskite films is also critical for preventing the moisture attack. As mentioned above, benzylamine passiva- tion can greatly increase the photovoltaic performance of perovskite devices. The benzylamine passivated perovskite films can stabilize for more than four months in humid air (55 ± 5 RH%) without any degradation (Fig. 4e). Theoretical simulations show that benzylamine molecules are edge-on packing on the perovskite surface, which can prevent the moisture attack effectively. 66 Photo curing of perovskite films. "Photo curing" means the photovoltaic performance of solar cell devices further increases by light soaking. 87 The phenomenon has been observed ...
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... reported that MAPbI 3 films illuminated in dry nitrogen shows a small rise in emission, and the internal Photolumines- cence quantum efficiency (PLQE) reaches a value of η = 12%. When the film is illuminated instead in dry air, the photolumines- cence (PL) rises substantially and the internal PLQE approaches η = 48% and continues to slowly rise (Fig. 4f). When the film is light soaked in humidified air (45% relative humidity), the internal PLQE plateaus at η = 89%. This is approaching PLQE values in which almost all of the non-radiative decay processes are eliminated. 121 It is supposed that the application of light with the right level of humidity causes electrons to bond with oxygen ...
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... In this part, a detailed study was conducted on the impact of defect states at the interfaces of various layers within a solar cell structure: ETL/MASnBr3, MASnBr3/CZTGS, CZTGS/HTL. Defect states can have a significant influence on the performance of solar cells, as they can trap charge carriers (electrons and holes), affect charge transport, and ultimately impact the overall efficiency of the device [39,40]. Table 5 shows the parameters used in the simulation. ...
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... [146][147][148][149][150][151][152] Therefore, the engineering of the grain boundaries to eliminate the detrimental trap states in polycrystalline thin films becomes a long-standing and important issue for high performance optoelectronic devices. [153][154][155][156][157] In addition to the detrimental trap states, understanding the defect properties of the surface and bulk perovskite films, grain boundary and surface passivation mechanisms, defect properties of the interface during engineering the device architecture is quite crucial aspect, which need serious 13 interface and defect engineering. 153,154 Moreover, Cs2TiBr6 is reported as a sensitive material to defect density 44,158,159 though it demonstrate power conversion efficiency of 14.8%. ...
... [153][154][155][156][157] In addition to the detrimental trap states, understanding the defect properties of the surface and bulk perovskite films, grain boundary and surface passivation mechanisms, defect properties of the interface during engineering the device architecture is quite crucial aspect, which need serious 13 interface and defect engineering. 153,154 Moreover, Cs2TiBr6 is reported as a sensitive material to defect density 44,158,159 though it demonstrate power conversion efficiency of 14.8%. 160 If all possible solar parameters are optimized this solar material is promising candidate in the future of peroveskite solar cells. ...
The stability issues in the widely known organic inorganic halide perovskite, CH3NH3PbI3, lead to the development of alternative halide double perovskite materials which get great attention in recent times. Although the stability issue seems promising, both materials and device performance of these photovoltaic materials remain inferior and challenging for improvements. Furthermore, the power conversion efficiency of single junction organic inorganic halide perovskite is now 24.2% and 29.15% for textured monolithic perovskite/silicon tandem solar cell, but for all-inorganic halide perovskite solar cell is 7.11% and halide double perovskite solar cells based on Cs2AgBiBr6 and Cs2TiBr6 is 2.8% and 3.3%, respectively, which is far less than 24.2% and 29.15%, respectively. This creates big question and concern that can both all-inorganic halide perovskite solar cell and halide double perovskites solar cells really be an acceptable alternatives to replace organic inorganic halide perovskite solar cells or lead based perovskite solar cells in the market in order to realize the sustainable practical applications? Not only this concern, but also there are many other big challenges facing by halide double perovskite solar cells. Such big challenges include: a) geometric constraints and limited integration with interfacial materials, b) dynamic disorder and a wide band gap and localized conduction band caused by cubic unit cell which restrains the interactions of orbitals, c) high processing temperature which may limit on the diverse applications, d) low electronic dimensionality making them less appropriate for single junction solar cell purpose and etc. Moreover, origin of electronic and optical properties such as the polarizability, the presence of molecular dipoles and their influence on the dynamics of the photo-excitations in the halide double perovskites remains unlock concern that need to be elucidated. Now, another big question is how to develop overcoming mechanisms for such challenges. Can we really overcome these current limitations faced by halide double perovskites so that we use them for sustainable commercialization? This research roadmap for performance improvement is suggested focusing on: materials surface and bulk engineering, band gap engineering, interfacial engineering, composition engineering, doping engineering, device architectural engineering, polar and domain order engineering. This was the reason that this review was developed in order to forward great contributions to the readers and commercial ventures.
... [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] However, in the prospect of commercial application, the advantages of solution processing also bring potential disadvantages of polycrystalline and single-crystal perovskites, including structural disorder and crystal defects. [32][33][34] Therefore, these surface and structural imperfections, mainly originating from uncoordinated halogen ions (X − ) and uncoordinated lead ions (Pb 2+ ), can result in an increase in trap states and the presence of cationic/halide vacancies. These imperfections subsequently initiate trap-assisted ion migration and nonradiative recombination. ...
Methylammonium lead bromide perovskite (MAPbBr3)-embedded nano- and micro-fibers are successfully fabricated by using the uniaxial electrospinning technique. Through the study of solidification and coordination between perovskite with hybrid polymers, polymethyl methacrylate, and polyacrylonitrile, the bamboo-like perovskite-embedded polymer nano/microfibers are unpredictably formed. Encapsulated in polymer, the passive perovskite-embedded polymer fibers exhibit a long-term fluorescence performance when simultaneously exposed to both water immersion and short-wavelength laser irradiation. Notably, due to the efficient gain media, the perovskite-rich region of the electrospun fiber can act as an optical microcavity. Multi-mode and single-mode lasing behaviors can be achieved via different cavity lengths. The mechanism of a microlaser within this perovskite fiber is confirmed through a Fabry–Pérot cavity, which provides an opportunity for optical components in lasers.
... Enhancing the quality of the crystal and achieving larger grain sizes have shown to be beneficial in minimizing the influence of bulk defects. To achieve this objective, various methods such as photo-curing and post-processing of thin films can be utilized [45,63]. ...
In this study, a novel Ge-Sn based perovskite solar cell (PSC) with the structure FTO/WS2/ FA0.75MA0.25Sn0.95Ge0.05I3/MoO3/Ag has been designed and thoroughly analyzed employing SCAPS-1D. Drawing attention from the work of Ito et al where a similar perovskite-based PSC displayed a poor performance of ∼ 4.48% PCE, in which a large conduction band offset (CBO) acts as a critical factor contributing to interfacial recombination and device deterioration. To address this issue, we presented WS2 as an electron transport layer (ETL) along with MoO3 as a hole transport layer (HTL), both possessing compatible CBO and valence band offset (VBO) with perovskite material. Through systematic simulations and optimizations, remarkable improvements in the PSC’s performance have been acquired, getting a power conversion efficiency (PCE) of 18.97%. The optimized structure involved a 50 nm MoO3 HTL, 350 nm FA0.75MA0.25Sn0.95Ge0.05I3 light-harvesting layer (LHL), and a 50 nm WS2 ETL. Bulk defect densities for the LHL and ETL were optimized to 1 × 10¹⁵ cm⁻³ and 1 × 10¹⁸ cm⁻³, respectively, significantly superior values than that of reported value in the literature. Particularly, the tolerable defect density of ETL has increased 1000 times more than the published literature. The interfacial tolerable trap density for MoO3/perovskite increased from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁶ cm⁻². The study also explored the impact of defects on quantum efficiency, revealing a severe negative influence beyond a perovskite bulk defect density of 1 × 10¹⁷ cm⁻³. Light intensity analysis demonstrated a correlation between incident light reduction and device performance decay. Capacitance–Voltage (C-V) and Mott–Schottky (M-S) have been analyzed during the study. Finally, the total recombination of the optimized device concerning thickness has been analyzed along with the dark J-V characteristics. The comprehensive insights gained from this work are anticipated to accelerate the fabrication of mixed Ge-Sn based PSCs with improved efficiency, paving the way for commercialization in the photovoltaic industry.
... However, recombination related to the mentioned shallow traps is considered to reduce the diffusion length of photoexcited carriers, leading to voltage losses. In other words, suppressing recombination through materials design of charge transport layers contributes to an increase in photovoltaic conversion efficiency [9][10][11][12][13][14]. ...
Tin oxide (SnO2) has been recognized as one of the beneficial components in the electron transport layer (ETL) of lead–halide perovskite solar cells (PSCs) due to its high electron mobility. The SnO2-based thin film serves for electron extraction and transport in the device, induced by light absorption at the perovskite layer. The focus of this paper is on the heat treatment of a nanoaggregate layer of single-nanometer-scale SnO2 particles in combination with another metal-dopant precursor to develop a new process for ETL in PSCs. The combined precursor solution of Li chloride and titanium(IV) isopropoxide (TTIP) was deposited onto the SnO2 layer. We varied the heat treatment conditions of the spin-coated films comprising double layers, i.e., an Li/TTIP precursor layer and SnO2 nanoparticle layer, to understand the effects of nanoparticle interconnection via sintering and the mixing ratio of the Li-dopant on the photovoltaic performance. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) measurements of the sintered nanoparticles suggested that an Li-doped solid solution of SnO2 with a small amount of TiO2 nanoparticles formed via heating. Interestingly, the bandgap of the Li-doped ETL samples was estimated to be 3.45 eV, indicating a narrower bandgap as compared to that of pure SnO2. This observation also supported the formation of an SnO2/TiO2 solid solution in the ETL. The utilization of such a nanoparticulate SnO2 film in combination with an Li/TTIP precursor could offer a new approach as an alternative to conventional SnO2 electron transport layers for optimizing the performance of lead–halide perovskite solar cells.
... Enhancing the quality of the crystal and achieving larger grain sizes have shown to be beneficial in minimizing the influence of bulk defects. To achieve this objective, various methods such as photo-curing and post-processing of thin films can be utilized [45,63]. ...
In this study, a novel Ge-Sn based perovskite solar cell (PSC) with the structure FTO/WS2/ FA0.75MA0.25Sn0.95Ge0.05I3/MoO3/Ag has been designed and thoroughly analyzed employing SCAPS-1D. Drawing attention from the work of Ito et al., where a similar perovskite-based PSC displayed a poor performance of ~ 4.48 % PCE, in which a large conduction band offset (CBO) acts as a critical factor contributing to interfacial recombination and device deterioration. To address this issue, we presented WS2 as an electron transport layer (ETL) along with MoO3 as a hole transport layer (HTL), both possessing compatible CBO and valence band offset (VBO) with perovskite material. Through systematic simulations and optimizations, remarkable improvements in the PSC's performance have been acquired, getting a power conversion efficiency (PCE) of 18.97%. The optimized structure involved a 50 nm MoO3 HTL, 350 nm FA0.75MA0.25Sn0.95Ge0.05I3 light-harvesting layer (LHL), and a 50 nm WS2 ETL. Bulk defect densities for the LHL and ETL were optimized to 1×1015 cm-3 and 1×1018 cm-3, respectively, significantly superior values than that of reported value in the literature. Particularly, the tolerable defect density of ETL has increased 1000 times than published literature. The interfacial tolerable trap density for MoO3/perovskite increased from 1×1014 cm-2 to 1×1016 cm-2. The study also explored the impact of defects on quantum efficiency, revealing a severe negative influence beyond a perovskite bulk defect density of 1×1017 cm-3. Light intensity analysis demonstrated a correlation between incident light reduction and device performance decay. Capacitance–Voltage (C-V) and Mott-Schottky (M-S) have been analyzed during the study. Finally, the total recombination of the optimized device concerning thickness has been analyzed along with the dark J-V characteristics. The comprehensive insights gained from this work are anticipated to accelerate the fabrication of mixed Ge-Sn based PSCs with improved efficiency, paving the way for commercialization in the photovoltaic industry.
... The fabrication of the first solid-state PSC is the groundbreaking work by Kim et al. [1] and elicits the PSCs to come on the track of the photovoltaic (PV) industry. The optoelectronic properties of perovskite materials, including high absorption coefficient, tunable direct bandgap, high carrier mobility, and bipolar carrier transport property, are favorable for achieving high power conversion efficiency in PSCs [2,3]. These features have received more attention, and in just one decade, the PCE of PSCs have raised from 3.8 % to 26.1 % [3][4][5]. ...
... However, the major problem with Sn-based PSCs is the oxidation of Sn 2+ ions into Sn 4+ ions, which works as unwanted p-type doping in the material, increasing the defects, which leads to the reduction in PCE. However, earlier results suggest that using some additives, such as SnF 2 and SnCl 2 in the perovskite precursor reduces the oxidation of the Sn 2+ ions, resulting in improved device performance. Hao et al. [25] have improved the device stability of Sn-based PSC compare to Pb-based PSC counterpart using SnF 2 as an additive in their Sn-based perovskite precursor solution. ...
The bipolar properties of perovskites make it fascinating to design a perovskite solar cell (PSC) without a hole transport layer (HTL). An HTL-free PSCs provide easy fabrication, are low-cost, and time-saving. In HTL-free PSCs, the crystallinity and morphology of perovskite film can enhance device performance. With the bifacial approach, the device efficiency can be further enhanced. In the present work, HTL-free bifacial PSCs have been simulated, and a strategy has been provided to design a high-performance device. In investigating the effect of various electron transport layers (ETLs) and lead-free perovskite layers, we observed that a suitable combination of ETL and perovskite is vital to achieve a higher power conversion efficiency (PCE). The Mott-Schottky analysis of ETL/perovskite interfaces reveals that the built-in potential depends on the bandgap of the perovskite absorber layer, which affects the device performance by setting up higher open circuit voltage (V OC). A higher dielectric material between the ETL and the perovskite layer improves the device performance. Additionally, lowering the doping density of the perovskite layer increases the bifacial factor of the device. While optimizing our cells, the champion device with configuration FTO/Zn 2 SnO 4 /MASnI 3 /UT-Au (ultra-thin gold) exhibits a PCE of 19.76 % and 15.97 % for the front and rear illumination, respectively. By replacing UT-Au with MAM(MoOx/Ag/MoOx) transparent conducting triple-layer electrode, our device shows an improved PCE of >25 % for both front and rear illumination. The outcomes of these studies are anticipated to be beneficial in designing and optimizing HTL-free bifacial PSCs in the experiment.
... The impact of shunt effects [128] and non-radiative losses [129] strongly manifests [129] in the operation of solar cells at low-light conditions when concentration of the photo-injected charge carriers is significantly reduced in comparison to standard 1 sun illumination. Potentially, photocarrier trapping at low-light intensities [130][131][132][133] in large-scale perovskite solar modules can critically affect the power output during morning, evening, or under shading conditions. To analyze the impact of HTL/perovskite interface properties on device performance under low-light conditions, we measured the IV characteristics of PSMs at outdoor ambient illumination with light intensity (I L ) ranging from ~30 to ~18 500 Lx (see photo-images on Fig. 8 (a)(b). ...
... The formation of deep trap states in the bulk of the perovskite films after the application of the MMSs leads to non-radiative recombination processes, eventually quenching the photoluminescence (see Fig. S11b in the Supporting Information) [72,73]. These traps can be formed by neutral and charged interstitial atoms of lead and iodide (Pb i and I i ) as well as neutral and charged states associated with antisites (Pb I and I Pb ) [74,75]. Defects located at grain boundaries and those induced by post-bending cracks (see Fig. S12 in the Supporting Information) primarily originate from the cleavage of chemical bonds, resulting in the generation of point defects. ...
... Defects located at grain boundaries and those induced by post-bending cracks (see Fig. S12 in the Supporting Information) primarily originate from the cleavage of chemical bonds, resulting in the generation of point defects. These defect sites can act as active centres for the trapping and recombination of photogenerated charge carriers within the perovskite active layer [74,76,77]. Finally, an increase in N t,s as an effect of applied MMSs can be attributed to an increase in the density of traps on the ETL/perovskite or/and HTL/perovskite interfaces due to cracking of the ETL or/and HTL layers [75,78]. ...
Halide perovskites are a promising class of novel photoactive materials for their application in flexible photovoltaic devices. Tolerance and stability of devices to various mechanical stresses are important aspects of this technology for its effective and long-term operation. Currently, this aspect has not been fully researched and addressed by the research community. Hence, this work is aimed at studying the effect of mild mechanical stresses (MMSs) induced by convex bending on the behaviour of ITO/ZnO/MAPbI3/Spiro-OMeTAD/Au slot-die-coated flexible perovskite solar cells (FPSCs) and investigating the underlying mechanisms leading to performance degradation in devices. The carrier generation, recombination, and extraction processes within FPSCs are investigated before and after the application of MMSs. The obtained results suggest that the photovoltaic performance of the FPSCs deteriorates by up to 50% after convex bending, due to increased non-radiative recombination losses. The results obtained in this work provide some valuable insights into the dynamics of recombination processes in FPSCs exposed to MMSs and can be used for developing new strategies for improving the mechanical stability of devices.
... This difference can result in varying concentrations of defects such as pinholes, cracks, increased surface roughness, less uniform composition distributions, high defect densities, and so on. 13,14 It is also important to note that different cell architectures, electrode designs, transparent conductive oxide (TCO) properties, and cell areas can result in different parasitic series resistances that can lead to significant PCE losses for larger dimensioned cells. ...
The power conversion efficiency (PCE) of spin-coated, ≪1 cm 2 , perovskite solar cells has exceeded 25%. The PCEs of the large-area perovskite solar cells made by scalable deposition techniques, however, are typically lower. One frequent element to improving performance in perovskites has been the utilization of nonscalable and low materials utilization, spin-based passivation treatments to reduce traps and defects in perovskite thin film absorber layers. Herein, we report a more sustainable passivation technique for large-area perovskite films via subsequent linear slot-die coating of a benzylammonium iodide (BAI) passivant formulation on the surface of previously deposited perovskite absorber layers. The BAI-passivated perovskite films demonstrate apparent larger grain size, higher photoluminescence (PL) intensity, reduced recombination rates as evidenced by longer PL lifetimes, and better spatial PL uniformity. The champion cell with optimized slot-die BAI passivation exhibited an improved PCE of ∼20.3%, as compared to 18.7% for the control device.
