Layer For Perovskite Solar Cells Research Articles

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.

Perovskites: Emergence of highly efficient third‐generation solar cells

For decades, human beings have been trying to plug into the sun to satisfy our energy requirements. Solar energy harvesting technology is, at present, in its third generation. Among the emerging photovoltaics, perovskite solar cells, which are fast advancing, have great future scope as solar energy harvesters. Rapid technological growth within the decade makes it the most potent among third-generation photovoltaics. Since its introduction in 2009, photoconversion efficiencies (PCE) of perovskite solar cells has hiked from 3.9% to 25.8% by 2021. Despite the swift increase in PCE, perovskite photovoltaics have to cross many hurdles to reach the stage of commercialization. Issues like low stability and lead toxicity are matters of great concern. The choice of material in each layer and the interfacial engineering to create matching between surfaces play a significant role in enhancing device performance. This review focuses on the materials and functions of four different layers of perovskite solar cells: light-absorbing, electron transport, hole transport, and counter electrodes. A brief discussion of perovskite-silicon tandem and 2D/3D multidimensional solar cells is also included in the review. The emergence of environment-friendly, economically feasible, and efficient solar cell materials turns out to be milestones in the path toward the commercialization of perovskite solar energy harvesters. Highlights This review discusses the emergence of perovskite solar cells, which are of great importance in the rapidly growing photovoltaic technology. An overview of materials, structure, and working of different perovskite solar cell layers- active layer, hole transport layer, electron transport layer, and counter electrode, is given in the review. The evolution of different solar cell materials is discussed, and their performance is compared qualitatively and quantitatively.

The role of plasmonic metal-oxides core-shell nanoparticles on the optical absorption of Perovskite solar cells

Among all the different methods to enhance the optical absorption of photovoltaic devices. The plasmonic effect is one the most prominent and effective ways to capture more incident light and also provide good carrier dynamic management. Here, we systematically introduce spherical gold nanoparticles (Au NPs) with different radii in the absorber layer of perovskite solar cells (PSCs). The overall enhanced optical absorption of around 14.20% and 20.02% is achieved for incorporated monolayer and bilayer Au NPs, respectively, in the active layer compared to the pure perovskite layer. Moreover, we employ the metal (Au)-dielectric (TiO2 and SiO2) nanoparticles in the absorber layer. The optical absorption increases as the core-shell size decreases. The optical absorption elevates in both Au@TiO2 core-shell and Au@SiO2 core-shell 17.5% and 3.5%, respectively. These results support superior separation and transfer of charge in the existence of plasmonic NPs. In addition, this study presents a very sophisticated approach to the optical enhancement of PSCs and thus helps to boost the overall photovoltaic device performance.

Enhanced charge transport characteristics in zinc oxide nanofibers via Mg2+ doping for electron transport layer in perovskite solar cells and antibacterial textiles

ZnO is well-known electron transport material; however, its charge carrier mobility is restricted due to lower conductivity and hysteresis losses. To overcome these issues, 1–3 wt% Mg-doped ZnO nanofibers were synthesized via electrospinning and then applied as electron transport layer (ETL) of perovskite solar cell. The structural, morphological, chemical composition, electronic structure, and optical activity of the synthesized nanofibers were studied to elucidate the role of Mg doping. X-ray diffraction of all nanofibers revealed that Mg was successfully incorporated into ZnO lattice and revealed that ZnO is present in hexagonal wurtzite structure. Optical characterization of the nanofibers revealed that with an increase in Mg 2+ doping concentration, the bandgap energy (Eg) tuned from 3.36 eV to 2.8 eV. It was observed that doping ZnO matrix with Mg ions improved the electronic structure, hence favoring the increase in the fill factor, current density, and efficiency. By doping 1, 2, and 3 wt% Mg into ZnO, efficiency was increased up to 8.48, 10.33, and 13.52%, respectively. Thus, a significant improvement in the performance of ZnO was noted by our proposed facile Mg doping. In addition, a significant improvement in photocatalytic activity was observed in Mg doped ZnO, which was used for fabrication of antibacterial textiles.

Recent progress of rare earth conversion material in perovskite solar cells: A mini review

• This review summarizes the application of rare earth material in solar cells. • The rare earth material application of perovskite solar cells is introduced. • The rare earth material improvement of solar cell is discussed. Organic-inorganic lead halide based perovskite solar cell has received broad interest due to their merits of low cost, a low temperature solution process, and high power conversion efficiency. Rare earth ion doped nanomaterials can be used in perovskite solar cell to expand the range of absorption spectra and improve the stability due to its up conversion and down conversion effect. This article reviews recently progress in using rare earth ion doped nanomaterials in mesoporous electrodes, perovskite active layers, and as an external function layer of perovskite solar cell. Finally, we discuss the challenges facing the effective use of rare earth ion doped nanomaterials in perovskite solar cell and present some prospects for future research.

Hydrogen-iodide bonding between glycine and perovskite greatly improve moisture stability for binary PSCs

In recent years, the maximum power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%. However, stability, especially under high relative humidity, has become a great obstacle for commercialization of perovskite devices due to its intrinsic defects. Interface modification is an effective method to improve the performance of PSCs for it could validly restrain defects and prevent decomposition of perovskite. In this paper, interface properties have been greatly improved by glycine (GLY) doped SnO 2 electron transport layer (ETL) in planar binary PSCs. SnO 2 -GLY ETL leads to improved band alignment, reduced charge recombination and enhanced electron mobility. XPS and NMR results demonstrate that the ammonia group in GLY combined with perovskite through hydrogen-iodide bonding, which greatly improves the moisture stability of the devices. The best PCE of the perovskite solar cell increased from 19.08% to 21.18%, and GLY modified devices can maintain 88% of its initial PCE after 7 days under 60 ± 5% relative humidity (RH) in ambient condition without any encapsulation. While, thermal stability test results indicating that hydrogen bonding is just a little helpful for improving stability at high temperature. This work indicates that forming hydrogen bonding between perovskite and ETL is an effective way to enhance moisture stability for commercialization of PSCs. • Interface properties between SnO 2 ETL and PSCs are improved by glycine (GLY), leading to enhanced PCE from 19.11% to 21.18%. • The amino group in GLY is bound to perovskite by hydrogen iodide bond, which greatly improves water stability of the device. • Long-term and thermal stability of the devices have also been improved.

Efficient and Stable Inverted Perovskite Solar Cells with Graphene Oxide‐Modified Hole Transport Layer

PTAA is widely applied as an ideal organic hole‐conducting material in perovskite solar cells (PSCs) and other advanced solar cells. However, its hydrophobicity makes it hard to be compatible with the adjacent perovskite. Herein, graphene oxide (GO) as an effective modifier for the PTAA layer in PSCs is introduced. Evidently, the surface wettability of PTAA and thus the morphology and quality of the as‐formed perovskite can be well controlled by tuning the conditions of GO treatment. Furthermore, characterization of optical and electrical properties shows significant passivation effect in the interface between PTAA and the absorber. As a result, the power conversion efficiency (PCE) of the device increases from 16.21% to 17.73% after GO treatment, with almost hysteresis‐less J–V characteristics. What's more, long‐term tests also indicate significant stabilization effect in the solar cells, with the PCE of encapsulated device being retained at 99.6% of the initial value after 42 days, while the reference device retains only 80.7%. Herein, new perspectives for more efficient and stable PSCs in the view of interface modification are provided.