Layer For Perovskite Solar Cells Research Articles

Crystallization and Defect Chemistry Dual Engineering for MAPbI3 Perovskite Solar Cells with Efficiency Approaching 22%

Methylammonium lead triiodide (MAPI) has been the most commonly used light absorber layer for perovskite solar cells and also shows potentially high theoretical efficiency. However, the achievable efficiencies so far still lag behind those of their formamidinium- or mixed cation-based counterparts. In this work, the dual additives 2-mercaptopyridine (2-MP) and 1,2-dichlorobenzene (DCB) are applied to regulate the crystal orientation, yielding a high-crystal quality MAPI film and passivating the trap states of the film. Encouragingly, we are able to distinguish the efficacy of the two additives. DCB effectively reduced the size of colloidal clusters in the perovskite precursor, thus helping the wet film reach the critical concentration to initialize rapid nucleation. The resulting MAPI film exhibited extended grain size with a stronger grain orientation and smoother surface. With the subsequent introduction of 2-MP, the high crystal quality was maintained, and 2-MP interacted with uncoordinated Pb defects and passivated the related traps. The dual additive-processed devices exhibited the champion efficiency of 21.83% with a simultaneously high Jsc of 24.01 mA/cm2 and Voc of 1.15 V. This work provides a means to engineer the crystallization quality and defect chemistry toward efficient MAPbI3 perovskite solar cells.

Recent Advances on Nanocrystals Embedding for High Performance Perovskite Solar Cells

AbstractInterfacial loss arising from defect trapping, contact barrier, and energy level alignment in the emerged perovskite solar cells (PSCs), is one of the most important issues to address for both improved photoconversion efficiency and long‐term operational stability. The recent endeavors on the interfacial embedding of nanocrystals (NCs) in desired locations of PSCs have shown great success in terms of eliminating the interfacial loss in PSCs, while there is a lack of review to summarize the advances of NCs embedding for improved carrier dynamics and inhibited environmental degradation. Present study systematically analyzes the recent achievements on the embedding of a series of NCs including carbon dots, perovskite NCs, II‐VI semiconductor NCs, metal/alloy NCs, which are intentionally introduced in desired layers/interfaces of PSCs. The specific functionality of the NCs embedding including carrier dynamic modulation, crystallinity enhancement, defect passivation, light trapping, and stability enhancement are sorted out, according to the requirement of each layer in PSCs. Finally, the current challenges and future perspectives of NCs embedding for perovskite‐based optoelectronic devices is outlook. The present study provides a guide for developing NCs‐based additives for high‐performance PSCs is believed.

Modification of SnO2 Electron Transport Layer in Perovskite Solar Cells.

Rapid development of the device performance of organic-inorganic lead halide perovskite solar cells (PSCs) are emerging as a promising photovoltaic technology. Current world-record efficiency of PSCs is based on tin oxide (SnO2) electron transport layers (ETLs), which are capable of being processed at low temperatures and possess high carrier mobilities with appropriate energy- band alignment and high optical transmittance. Modification of SnO2 has been intensely investigated by various approaches to tailor its conductivity, band alignment, defects, morphology, and interface properties. This review article organizes recent developments of modifying SnO2 ETLs to PSC advancement using surface and bulk modifications, while concentrating on photovoltaic (PV) device performance and long-term stability. Future outlooks for SnO2 ETLs in PSC research and obstacles remaining for commercialization are also discussed.

Studying the effect of changing the thickness of the layers of the perovskite solar cell (ZnTe /CH3NH3PbI3 /TiO2/ZnO/FTO) using the simulation program (SCAPS 1-D)

This research includes a study of the effect of the thickness of each layer of perovskite solar cell (CH3NH3PbI3) /TiO2/ZnO/FTO) and selecting the best thickness to obtain the highest efficiency of the cell, and studying the effect of adding a back surfsce layer on the efficiency of the solar cell using (SCAPS1-D). The perovskite (CH3NH3PbI3) was adopted as absorption layer and its thickness tested from (1-7µm) with an increase of (1µm) to obtain the best thickness for best efficiency of the solar cell, its best thickness was (5µm), the thickness of the buffer layer (TiO2) was tested from (0.5-1.5 µm) with an increase of (0.25µm) and its best thickness was (0.5 µm), the thickness of the transparent conduction oxide (FTO) layer was tested (0.1-1.1µm) with an increase of (0.2µm) and its best thickness was (0.1 µm) and the thickness of the window layer(ZnO) was tested (0.1-0.5 µm) with an increase of (0.1µm) and its best thickness was (0.1µm).The effect of the window layer on the thickness of the buffer layer was studied and it was found that the best thickness of the buffer layer is (0.05µm). Finally, a back surface field layer was added, which is zinc telluride (ZnTe) with a thickness of (0.1 µm) and its thickness was studied, and its best thickness was (0.05µm) .It was found that the best thickness of the absorbent layer after adding the back surface field layer is (1µm). The final outputs of the cell were as follows: Voc=1.288(V), Jsc=25mA/cm2, FF=89.55%, ƞ=28.82%

Back Cover Image

AbstractThis cover (DOI: 10.1002/inf2.12345) shows a multifunctional TPA‐azaBODIPY‐TPA small molecule with superior optoelectronic and photophysical properties. Material is shown to function as an efficient hole transport layer in perovskite solar cells reaching a power conversion efficiency of 17.4%, and as a robust electron donor in near‐infrared organic photodetectors absorbing light in the wavelength range of up to 800 nm. Offering two distinct optoelectronic functions, TPA‐azaBODIPY‐TPA is particularly attractive as it enables multi‐purpose applications while maintaining the ease of fabrication. image

Vitamin Natural Molecule Enabled Highly Efficient and Stable Planar n–p Homojunction Perovskite Solar Cells with Efficiency Exceeding 24.2%

AbstractThe defect passivation and interface energetics‐modification between perovskite and transport layers are significant for the further improvement of efficiency and stability of perovskite solar cells (PSCs). Here, a double‐layer modification engineering strategy is employed by different functionalized natural vitamins into the electron transport layer and perovskite, respectively. Considering the different role of each functional layer in PSCs, the vitamin C (VC) with high conductivity is introduced into SnO2, showing electron mobility enhancement, an interface energy‐levels offsets reduction, and enhanced interfacial charge transfer. Meanwhile, antioxidant vitamin D2 (VD2) with multiple passivating functional groups is introduced into the perovskite bulk to moderately tailor its intrinsic characteristics. The surface energetics of perovskite are changed from n‐type to p‐type, the thickness of the p‐type perovskite is 80 nm, thus the spontaneous n–p homojunction is formed in perovskite caused by VD2, which increases the built‐in electric field and the efficiency of perovskite hole extraction. The synergistic effect of VC and VD2 better heightens the charge extraction efficiency and achieves charge‐carrier transport balance in PSCs. The optimum device achieves a power conversion efficiency of 24.20% and a fill factor of 81.01% with negligible hysteresis. This efficiency is among the best PSCs employing natural molecules reported so far.

Tailored fabrication of quasi-isoporous and double layered α-Fe2O3 thin films and their application in photovoltaic devices

A series of α-Fe2O3 thin films with distinct morphologies are prepared via a facile polystyrene-block-polyethylene oxide templated sol–gel method. By tailoring the poor solvent contents and FeCl3-to-polymer weight ratio in the sol–gel solutions, quasi-isoporous α-Fe2O3 thin films with different substructures and thicknesses are obtained. Via a thermal annealing post-treatment, double layered structures are induced by a synergistic dewetting and Oswald ripening effect. Special focus is set on the α-Fe2O3 thin films prepared with no annealing/annealing-medium FeCl3 concentration, as they possess uniform periodic structures, which is suitable to be used as hole blocking modification layer of perovskite solar cells (PSCs). An improved power conversion efficiency (PCE) is obtained when the double layered α-Fe2O3 thin film is applied as the hole blocking modification layer for PSCs. The improved PCE primarily originates from the increased VOC, which probably benefits from the synergistic effect of the suppressed charge carrier recombination at the interfaces, the enhanced light transmittance as well as the superior electron extraction capacity.

The Investigation of the Influence of a Cu2O Buffer Layer on Hole Transport Layers in MAPbI3-Based Perovskite Solar Cells.

The passivation engineering of the hole transport layer in perovskite solar cells (PSCs) has significantly decreased carrier accumulation and open circuit voltage (Voc) loss, as well as energy band mismatching, thus achieving the goal of high-power conversion efficiency. However, most devices incorporating organic/inorganic buffer layers suffer from poor stability and low efficiency. In this article, we have proposed an inorganic buffer layer of Cu2O, which has achieved high efficiency on lower work function metals and various frequently used hole transport layers (HTLs). Once the Cu2O buffer layer was applied to modify the Cu/PTAA interface, the device exhibited a high Voc of 1.20 V, a high FF of 75.92%, and an enhanced PCE of 22.49% versus a Voc of 1.12 V, FF of 69.16%, and PCE of 18.99% from the (PTAA/Cu) n-i-p structure. Our simulation showed that the application of a Cu2O buffer layer improved the interfacial contact and energy alignment, promoting the carrier transportation and reducing the charge accumulation. Furthermore, we optimized the combinations of the thicknesses of the Cu2O, the absorber layer, and PTAA to obtain the best performance for Cu-based perovskite solar cells. Eventually, we explored the effect of the defect density between the HTL/absorber interface and the absorber/ETL interface on the device and recommended the appropriate reference defect density for experimental research. This work provides guidance for improving the experimental efficiency and reducing the cost of perovskite solar cells.

Dual‐Phase Stabilized Perovskite Nanowires for Reduced Defects and Longer Carrier Lifetime

Abstract1D perovskite materials are of significant interest to build a new class of nanostructures for electronic and optoelectronic applications. However, the study of colloidal perovskite nanowires (PNWs) lags far behind those of other established perovskite materials such as perovskite quantum dots and perovskite thin films. Herein, a dual‐phase passivation strategy to synthesize all‐inorganic PNWs with minimized surface defects is reported. The local phase transition from CsPbBr3 to CsPb2Br5 in PNWs increases the photoluminescence quantum yield, carrier lifetime, and water‐resistivity, owing to the energetic and chemical passivation effect. In addition, these dual‐phase PNWs are employed as an interfacial layer in perovskite solar cells (PSCs). The enhanced surface passivation results in an efficient carrier transfer in PSCs, which is a critical enabler to increase the power conversion efficiency (PCE) to 22.87%, while the device without PNWs exhibits a PCE of 20.74%. The proposed strategy provides a surface passivation platform in 1D perovskites, which can lead to the development of novel nanostructures for future optoelectronic devices.

Electron transport engineering with different types of titanium dioxide nanostructures in perovskite solar cells

The light-harvesting effects and electron transport engineering could be achieved by manipulating electron transport layer (ETL) morphology. In This research, three variant nanostructures (NSs) of titanium dioxide (TiO2) have been applied as the ETL in conventional structure of perovskite solar cells (PSCs). Device structures of FTO/TiO2 compact layer/TiO2 NS layer/Perovskite/Spiro-OMeTAD/Au are used for the fabrication of PSCs in ambient conditions. Zero and one-dimensional structures of TiO2 including TiO2 nanocrystals (NCs) with the dominant size of 25 nm, TiO2 nanorods (NRs) with diameters and lengths about 80 nm and 1–2 µm, and TiO2 nanofibers (NFs) with the same dimensional parameters of 100 nm and 2–12 µm were prepared through the hydrothermal method. Then the effects of ETL morphology on the electron transporting process, interfacial engineering, surface quality and cell performance have been investigated. Triple Cation Cs0.05(MA0.17-FA0.83)0.95Pb(I0.83Br0.17)3 perovskite is also used as the light harvester layer in PSCs due to its proper band gap energy, crystalline quality and longtime stability. According to the results, one-dimensional (1D) TiO2 nanostructures with medium size released the best current density of 21.9 mA/cm2 and maximum filling factor of 0.7. That is while the incomplete pore filling of the sublayer and lower open circuit voltage (VOC) 0.905 V had negative impacts on the power conversion efficiency of TiO2 NRs included perovskite solar cells. Remarkable results were achieved for the PSC with zero-dimensional (0D) TiO2 nanostructures as the compact ETL and highest VOC of 1.02 V led to the maximum power conversion efficiency of 14.88 % in ambient conditions.

Bismuth iron tungstate pyrochlore thin films for photovoltaic applications

Thin films based on the ternary complex oxide Bi0.50Fe0.4WOq with a cubic pyrochlore structure were obtained and used for the first time as electron-transport layers in perovskite solar cells. The measured power conversion efficiency was ∼ 4 rel% higher than that of state-of-the-art TiO2-based perovskite solar cells.

Low-Temperature-Processed Monolayer Inverse Opal SnO2 Scaffold for Efficient Perovskite Solar Cells.

Organic-inorganic halide perovskite solar cells (PSCs) have attracted tremendous attention in the photovoltaic field due to their excellent optical properties and simple fabrication process. However, the recombination of photogenerated electron-hole pairs at the interface severely affects the power conversion efficiency (PCE) of the PSCs. Herein, a monolayer of inverse opal SnO2 (IO-SnO2 ) is synthesized via a template-assisted method and used as a scaffold for perovskite layer (PSK). The porous IO-SnO2 scaffold increases the contact area and shortens the transport distance between the electron transport layer (ETL) and PSK. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy results indicate that the built-in electric field is enhanced with IO-SnO2 scaffold, strengthening the driving force for charge separation. Femtosecond transient absorption spectroscopy measurements reveal that the IO-SnO2 scaffold facilitates interfacial electron transfer from PSK to ETL. Based on the above superiorities, the IO-SnO2 -based PSCs exhibit boosted PCE and device stability compared with the pristine PSCs. This work provides insights into the development of novel scaffold layers for high-performance PSCs.

Automated Machine Learning Approach in Material Discovery of Hole Selective Layers for Perovskite Solar Cells

In the emerging field of perovskite solar cells, rational hole selective layer development is considered a double engine of this progress. To tap into the full potential and accelerate the commercialization path, machine learning (ML) is being tasked for perovskite screening. However, sincere efforts have not led to the design of hole selective layers based on the different organic core groups to yield efficient solar cells. Herein, it is demonstrated how ML can be applied to the advancement of hole transport materials (HTMs). The influence of HTMs with various core groups on the optoelectronic features and photovoltaic performance is evaluated and it is validated using both the random forest model and AutoML framework, General Automated Machine Learning Assistant (GAMA). To this end, the GAMA is utilized to predict the suitability of HTMs and it returns a 0.0542 ± 0.0470 RMSE score for 15 different materials on average. Correlation between experimental and predicted results is established, and GAMA is implemented for HTM suitability prediction. This paves the way for judicious and effective ways of the development of HTMs. In particular, the prediction approach from GAMA is an effective, reliable, and fast methodology and is pioneering in the field of HTM screening.

Understanding the Space-Charge Layer in SnO2 for Enhanced Electron Extraction in Hybrid Perovskite Solar Cells.

Tin oxide (SnO2) has been widely used as an n-type metal oxide electron transport layer in perovskite solar cells (PSCs) owing to its superior electrical and optical properties and low-temperature synthesis process. In particular, the interfacial effect between indium tin oxide (ITO) and SnO2 is an important parameter that controls the charge transport properties and device performance of the PSCs. Therefore, understanding the interfacial effect of ITO/SnO2 and its role in PSCs is crucial, but it is not studied intensively. Herein, we investigated the space-charge effect at the interface of ITO/SnO2 using transfer length measurement and conductive atomic force microscopy as a function of SnO2 thickness. Moreover, optical, morphologic, and device measurements were performed to determine the optimal SnO2 thickness for PSCs. The space-charge effect was identified in ITO/SnO2 when the SnO2 layer was very thin due to electron depletion near the interface. Interestingly, a critical kink point was observed at approximately 10 nm SnO2 thickness, indicating the electron depletion and weak charge transfer behavior of the device. Thus, a thickness around 20 nm was favorable for the best PSC performance because charge transport behavior in the thin SnO2 layer was depressed by electron depletion. However, when the thickness of SnO2 exceeded 50 nm, the device performance deteriorated due to increased series resistance. This study provides a strategy to tune the electron transport layer and boost the charge transport behavior in PSCs, making important contributions to optimizing SnO2-based PSCs.

Exploring π-extended subporphyrinoids as electron transporting materials in perovskite solar cells

Due to their strong acceptor properties and enhanced charge transport capabilities, non-fullerene electron acceptors based on [Formula: see text]-extended derivatives – subnaphthalocyanines (SubNc) or subphtalocyanine dimers (SubPc[Formula: see text] – have been employed in organic photovoltaics in the past as an alternative to the expensive fullerene. However, these promising [Formula: see text]-extended derivatives have not been explored in perovskite solar cell technology. In this work, we implement a vacuum-deposited very thin film of SubNc or SubPc2 as electron transport layers in perovskite solar cells. In particular, we demonstrate the excellent electron extraction properties of the thin films in contact with perovskite layer. The fabricated perovskite solar cells exhibit enhanced device performances with reduced hysteresis index and improved device stability. Our results validate the use of [Formula: see text]-extended subporphyrinoids as promising candidates for perovskite optoelectronics with enhanced stability properties, being essential for further commercialization of the perovskite technology.

Recent development in electron transport layers for efficient tin-based perovskite solar cells

Hybrid organic-inorganic tin (Sn)-based perovskite materials became a promising choice as an alternative to lead-free perovskite solar cells (PSCs) due to their outstanding optical and electrical properties. But, so far, a power conversion efficiency (PCE) of only 13% has been achieved for Sn-based PSCs. To achieve highly efficient and stable PSCs, not only the properties of the active layer but the charge selective contacts (electron and hole transport layers) should be selected wisely. The interfaces between the perovskite active layer and charge transport layers play an important role in achieving the better performance of PSCs. In the present review, the spotlight is on the recent developments made on the optimization of electron transport layers (ETLs) for the efficient Sn-based hybrid organic-inorganic PSCs. Further, we comprehensively discuss the significance and the impact of the lowest unoccupied molecular orbital level of electron transport material on the charge transport, which additionally affects the photovoltaic performance of the device. In summary, with continuous research on the Sn-based hybrid organic-inorganic perovskite materials as an absorbing layer, conventional ETLs (metal oxides) cannot be used. Thus, the optimum candidate for befitted ETLs must be explored and investigated in detail for efficient PSCs.

Effect of Li-doped TiO2 layer on the photoelectric performance of carbon-based CsPbIBr2 perovskite solar cell

Carbon-based CsPbIBr2 perovskite solar cells (PSCs) have attracted much attention due to their excellent photoelectric properties and low cost fabrication processes. The TiO2 has been diffusely employed as electron-transporting layer (ETL) for carbon-based CsPbIBr2 PSC. However, the lower electron mobility for TiO2 restricts the performance improvement. The tactics of ion doping is normally used to improve the ETL performance. In this study, Li-doped TiO2 (Li: TiO2) is used as a novel ETL for carbon-based planar CsPbIBr2 PSC. There is no change in the optical band gap of TiO2 after the incorporation of Li. However, Li-doping can effectively improve the crystallinity of TiO2 film and reduce the dark current and charge recombination of CsPbIBr2 PSC. Comparing with the TiO2-based CsPbIBr2 PSC, the efficiency of CsPbIBr2 PSC with the Li: TiO2 ETL increases from 6.63% to 8.09%. Additionally, the use of the Li: TiO2 ETL also has a positive impact on the long-term stability of the CsPbIBr2 PSC. This work indicates that ion doping can offer a new route to produce effective ETL for the development of highly-efficient CsPbIBr2 solar cell with a interface engineering concept.

Application of ethyl acetoacetate bifocal additive for achieving high-performance perovskite solar cells

Perovskite layer in perovskite solar cells (PSCs) is usually polycrystalline structure with relatively small crystal size, many grain boundaries and a large number of defects, which will be one of the main reasons that limit the improvement of their photovoltaic performance and stability. Hence, improving the film quality and reducing the defect density for perovskite layer are the key to prepare high-performance PSCs. Herein, the ethyl acetoacetate (EAA) containing two functional groups of CO and –COO is introduced into perovskite precursor solution as a novel bifocal additive, which could not only promote the growth of perovskite, but also effectively deactivate the defect. The results display that EAA can increase the crystallinity and average grain sizes, effectively reduce the defects and significantly restrain the defect-assisted non-radiative recombination, attributing to the strong interaction between EAA and Pb2+ in perovskite. As a result, the perovskite film with EAA shows better film-quality, reduced defects, and suppressed defect-assisted non-radiative recombination. Hence, the EAA device achieves a high PCE of 22.08% with a markedly enhanced open-circuit voltage of 1.15 V. More importantly, the EAA perovskite exhibits excellent humidity stability. The perovskite devices with high water contact angle of 84.4° can retain around 80% of their initial PCEs under 40% RH for 4000 h. The results afford an easy but effective method to high-quality perovskite films with reduced defect density for highly efficient and stable PSCs.

Automated Machine Learning Approach in Material Discovery of Hole Selective Layers for Perovskite Solar Cells

Automated Machine Learning Approach in Material Discovery of Hole Selective Layers for Perovskite Solar Cells

Nickel compound quantum dots as inorganic hole transporting layer in perovskite solar cells

Nickel oxide has grabbed the attention as one the most efficient materials for inorganic hole transporting layer in perovskite solar cells. However, it is quite a challenge to control the growth conditions of NiO film. In this work, the nickel compound quantum dots prepared via the electrochemical process are investigated as HTL for the PSCs. From absorbance spectra, the mixed phase of NiCl2 and NiOOH are observed. The average size of nickel compound quantum dots is about 2–4 nm from transmission electron microscopy. The solutions of nickel compound quantum dots are used to fabricate the PSCs with a p-i-n structure consisting of Fluorine doped Tin Oxide glass/nickel compound quantum dot/perovskite/PCBM/Ag. It is found that the NiO films prepared from nickel compound quantum dots show the full covered film, resulting in higher power conversion efficiency of 12.47% as compared to that of the reference NiCl2. The improvement in efficiency can be explained by increasing short circuit current density and fill factor. In addition, the stability of PSC based on nickel compound quantum dots demonstrates higher stability than the other condition. Thus, PSCs based on nickel compound quantum dots can be used to improve the interface of HTL and perovskite layer in PSC and result in the enhancement of the PSC performance.