Aqueous-Containing Precursor Solutions for Efficient Perovskite Solar Cells

Ecofriendly Solution Processing of Perovskite Solar Cells Using Water

Perovskite solar cells (PSCs) represent a promising avenue for producing cost-effective solar energy by harnessing sunlight, but challenges persist in their solution processing, which uses a large amount of organic solvent for existing PSC technology. The use of water as a solvent offers an environmentally friendly alternative to traditional solvents, aligning with the global drive for sustainable renewable energy technologies. This Perspective provides an overview of research in the area of PSC fabrication using water as a solvent, highlighting key advancements in the synthesis process. We delve into the kinetics of crystallization and the physical-chemical transformations of perovskite materials in water-based solution processing. Key challenges of the scalability of water-based solution processing for PSC fabrication are discussed. The Perspective sheds light on the broader potential for enhancing the ecofriendliness of perovskite solar cell technologies.

MXene-based novel nanocomposites doped SnO2 for boosting the performance of perovskite solar cells

Since being first published in 2018, the use of two-dimensional MXene in solar cells has attracted significant interest. This study presents, for the first time, the synthesis of an efficient hybrid electrocatalyst in the form of a nanocomposite (MXene/CoS)-SnO2 designed to function as a high-performance electron transfer layer (ETL). The study can be divided into three distinct parts. The first part involves the synthesis of single-layer Ti3C2Tx MXene nanosheets, followed by the preparation of a CoS solution. Subsequently, in the second part, the fabrication of MXene/CoS heterostructure nanocomposites is carried out, and a comprehensive characterization is conducted to evaluate the physical, structural, and optical properties. In the third part, the attention is on the crucial characterizations of the novel nanocomposite-electron transport layer (ETL) solution, significantly contributing to the evolution of perovskite solar cells. Upon optimising the composition, an exceptional power conversion efficiency of more than 17.69% is attained from 13.81% of the control devices with fill factor (FF), short-circuit current density (Jsc), and open-circuit voltage (Voc) were 66.51%, 20.74 mA/cm2, and 1.282 V. Therefore, this PCE is 21.93% higher than the control device. The groundbreaking MXene/CoS (2 mg mL-1) strategy reported in this research represents a promising and innovative avenue for the realization of highly efficient perovskite solar cells.

Atmospheric Humidity Underlies Irreproducibility of Formamidinium Lead Iodide Perovskites

Metal halide perovskite solar cells (PSCs) are infamous for their batch-to-batch and lab-to-lab irreproducibility in terms of stability and performance. Reproducible fabrication of PSCs is a critical requirement for market viability and practical commercialization. PSC irreproducibility plagues all levels of the community; from institutional research laboratories, start-up companies, to large established corporations. In this work, the critical function of atmospheric humidity to regulate the crystallization and stabilization of formamidinium lead triiodide (FAPbI3) perovskites is unraveled. It is demonstrated that the humidity content during processing induces profound variations in perovskite stoichiometry, thermodynamic stability, and optoelectronic quality. Almost counterintuitively, it is shown that the presence of humidity is perhaps indispensable to reproduce phase-stable and efficient FAPbI3-based PSCs.

High-Quality Hybrid Perovskite Thin Films by Post-Treatment Technologies in Photovoltaic Applications

Incredible progress in photovoltaic devices based on hybrid perovskite materials has been made in the past few decades, and a record-certified power conversion efficiency (PCE) of over 26% has been achieved in single-junction perovskite solar cells (PSCs). In the fabrication of high-efficiency PSCs, the postprocessing procedures toward perovskites are essential for designing high-quality perovskite thin films; developing efficient and reliable post-treatment techniques is very important to promote the progress of PSCs. Here, recent post-treatment technological reforms toward perovskite thin films are summarized, and the principal functions of the post-treatment strategies on the design of high-quality perovskite films have been thoroughly analyzed by dividing into two categories in this review: thermal annealing (TA)-related technique and TA-free technique. The latest research progress of the above two types of post-treatment techniques is summarized and discussed, focusing on the optimization of postprocessing conditions, the regulation of perovskite qualities, and the enhancement of device performance. Finally, an outlook of the prospect trends and future challenges for the fabrication of the perovskite layer and the production of highly efficient PSCs is given.

Identification the Role of Grain Boundaries in Polycrystalline Photovoltaics via Advanced Atomic Force Microscope

Atomicforce microscopy (AFM)-based scanning probing techniques, including Kelvinprobe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM), have been widely applied to investigate thelocal electromagnetic, physical, or molecular characteristics of functional materials on a microscopic scale. The microscopic inhomogeneities of the electronic properties of polycrystalline photovoltaic materials can be examined by these advanced AFM techniques, which bridge the local properties of materials to overall device performance and guide the optimization of the photovoltaic devices. In this review, the critical roles of local optoelectronic heterogeneities, especially at grain interiors (GIs) and grain boundaries (GBs) of polycrystalline photovoltaic materials, including versatile polycrystalline silicon, inorganic compound materials, and emerging halide perovskites, studied by KPFM and C-AFM, are systematically identified. How the band alignment and electrical properties of GIs and GBs affect the carrier transport behavior are discussed from the respective of photovoltaic research. Further exploiting the potential of such AFM-based techniques upon a summary of their up-to-date applications in polycrystalline photovoltaic materials is beneficial to acomprehensive understanding of the design and manipulation principles of thenovel solar cells and facilitating the development of the next-generation photovoltaics and optoelectronics.

Mechanism of Interaction of Water above the Methylammonium Lead Iodide Perovskite Nanocluster: Size Effect and Water-Induced Defective States

Water is often viewed as detrimental to organic halide perovskite stability. However, evidence highlights its efficacy as a solvent during organic perovskite liquid synthesis. This paradox prompts an investigation into water's influence on perovskite nanoclusters. Employing first principle calculations and ab initio molecular dynamics simulations, surprisingly, we discover some subsurface layers of methylammonium lead iodide (MAPbI3) nanoclusters exhibit stronger relaxation than surface layers. Moreover, a strong quantum confinement effect enhances the band gap of MAPbI3 as the nanocluster size decreases. Notably, the water molecules above MAPbI3 nanoclusters induce rich localized defect states, generating low-lying shallow states above the valence band for the small amounts of surface water molecules and band-like deep states across the whole gap for large nanoclusters. This work provides insights into water's role in the electronic structure and structural evolution of perovskite nanoclusters, aiding the design of water-resistant layers to protect perovskite quantum dots from ambient humidity.

Green solvents, materials, and lead-free semiconductors for sustainable fabrication of perovskite solar cells

Perovskite materials research has received unprecedented recognition due to its applications in photovoltaics, LEDs, and other large area low-cost electronics. The exceptional improvement in the photovoltaic conversion efficiency of Perovskite solar cells (PSCs) achieved over the last decade has prompted efforts to develop and optimize device fabrication technologies for the industrial and commercial space. However, unstable operation in outdoor environments and toxicity of the employed materials and solvents have hindered this proposition. While their optoelectronic properties are extensively studied, the environmental impacts of the materials and manufacturing methods require further attention. This review summarizes and discusses green and environment-friendly methods for fabricating PSCs, particularly non-toxic solvents, and lead-free alternatives. Greener solvent choices are surveyed for all the solar cell films, (i.e. electron and hole transport, semiconductor, and electrode layers) and their impact on thin film quality, morphology and device performance is explored. We also discuss lead content in perovskites, its environmental impact and sequestration routes, and progress in replacing lead with greener alternatives. This review provides an analysis of sustainable green routes in perovskite solar cell fabrication, discussing the impact of each layer in the device stack, via life cycle analysis.

Comprehensive review of environmental factors influencing the performance of photovoltaic panels: Concern over emissions at various phases throughout the lifecycle

Recently, solar photovoltaic (PV) technology has shown tremendous growth among all renewable energy sectors. The attractiveness of a PV system depends deeply of the module and it is primarily determined by its performance. The quantity of electricity and power generated by a PV cell is contingent upon a number of parameters that can be intrinsic to the PV system itself, external or environmental. Thus, to improve the PV panel performance and lifetime, it is crucial to recognize the main parameters that directly influence the module during its operational lifetime. Among these parameters there are numerous factors that positively impact a PV system including the temperature of the solar panel, humidity, wind speed, amount of light, altitude and barometric pressure. On the other hand, the module can be exposed to simultaneous environmental stresses such as dust accumulation, shading and pollution factors. All these factors can gradually decrease the performance of the PV panel. This review not only provides the factors impacting PV panel's performance but also discusses the degradation and failure parameters that can usually affect the PV technology. The major points include: 1) Total quantity of energy extracted from a photovoltaic module is impacted on a daily, quarterly, seasonal, and yearly scale by the amount of dust formed on the surface of the module. 2) Climatic conditions as high temperatures and relative humidity affect the operation of solar cells by more than 70% and lead to a considerable decrease in solar cells efficiency. 3) The PV module current can be affected by soft shading while the voltage does not vary. In the case of hard shadowing, the performance of the photovoltaic module is determined by whether some or all of the cells of the module are shaded. 4) Compared to more traditional forms of energy production, PV systems offer a significant number of advantages to the environment. Nevertheless, these systems can procure greenhouse gas emissions, especially during the production stages. In conclusion, this study underlines the importance of considering multiple parameters while evaluating the performance of photovoltaic modules. Environmental factors can have a major impact on the performance of a PV system. It is critical to consider these factors, as well as intrinsic and other intermediate factors, to optimize the performance of solar energy systems. In addition, continuous monitoring and maintenance of PV systems is essential to ensure maximum efficiency and performance.

Water-Regulated Lead Halide Perovskites Precursor Solution: Perovskite Structure Making and Breaking

Identifying the impact of water on iodoplumbate complexes in various solutions is essential for linking the coordination environment of the perovskite precursor to its final perovskite solar cell (PSC) properties. In this study, we propose a digital twin approach based on X-ray absorption fine structure and molecular dynamic simulation to investigate the structure evolution of iodoplumbate complexes in precursor solutions as a function of storage time under a constant humidity environment. A full picture about what water does in the perovskite formation process is brought out, and the "making and breaking" role of water molecules is uncovered to link the structure of iodoplumbate complexes to its final properties. This study sheds light on a full picture about what water does in the perovskite formation process and the role of water, which will lead to developing water-involved strategies for consistent PSC fabrication under ambient conditions.

High Power-Conversion Efficiency of Lead-Free Perovskite Solar Cells: A Theoretical Investigation

Solar cells based on lead-free perovskite have demonstrated great potential for next-generation renewable energy. The SCAPS-1D simulation software was used in this study to perform novel device modelling of a lead-free perovskite solar cell of the architecture ITO/WS₂/CH₃NH₃SnI₃/P3HT/Au. For the performance evaluation, an optimization process of the different parameters such as thickness, bandgap, doping concentration, etc., was conducted. Extensive optimization of the thickness and doping density of the absorber and electron transport layer resulted in a maximum power-conversion efficiency of 33.46% for our designed solar cell. Because of the short diffusion length and higher defect density in thicker perovskite, an absorber thickness of 1.2 µm is recommended for optimal solar cell performance. Therefore, we expect that our findings will pave the way for the development of lead-free and highly effective perovskite solar cells.

A Nontoxic NFM Solvent for High-Efficiency Perovskite Solar Cells with a Widened Processing Window

With the steady industrialization process of the perovskite solar cells (PSCs), the toxicity of the used solvents has become a pivotal issue that needs to be addressed. Especially, the usage of N,N-dimethylformamide (DMF) solvent would pose serious environmental and health concerns. Herein, we have reported a nontoxic solvent N-formylmorpholine (NFM) to replace the toxic DMF and have achieved a higher PCE of 22.78% compared to 21.97% when DMF was adopted. Moreover, with NFM, a widened antisolvent processing window was observed, facilitating the fabrication of PSCs with high reproducibility. This solvent engineering strategy offers an important solution to prepare eco-friendly, efficient, and stable perovskite solar cells.

MXene Based Nanocomposites for Recent Solar Energy Technologies

This article discusses the design and preparation of a modified MXene-based nanocomposite for increasing the power conversion efficiency and long-term stability of perovskite solar cells. The MXene family of materials among 2D nanomaterials has shown considerable promise in enhancing solar cell performance because of their remarkable surface-enhanced characteristics. Firstly, there are a variety of approaches to making MXene-reinforced composites, from solution mixing to powder metallurgy. In addition, their outstanding features, including high electrical conductivity, Young's modulus, and distinctive shape, make them very advantageous for composite synthesis. In contrast, its excellent chemical stability, electronic conductivity, tunable band gaps, and ion intercalation make it a promising contender for various applications. Photovoltaic devices, which turn sunlight into electricity, are an exciting new area of research for sustainable power. Based on an analysis of recent articles, the hydro-thermal method has been widely used for synthesizing MXene-based nano-composites because of the easiness of fabrication and low cost. Finally, we identify new perspectives for adjusting the performance of MXene for various nanocomposites by controlling the composition of the two-dimensional transition metal MXene phase.

Photoelectrochemical Properties, Machine Learning, and Symbolic Regression for Molecularly Engineered Halide Perovskite Materials in Water

The machine learning techniques are capable of predicting virtual material design space and optimizing material fabrication parameters. In this article, we construct machine learning models to describe the photoelectrochemical properties of molecularly engineered halide perovskite materials based on CH₃NH₃PbI₃ in an aqueous solution and predict a complex multidimensional design space for the halide perovskite materials. The machine learning models are trained and tested based on an experimental photocurrent data set consisting of 360 data points with varying experimental conditions and dye structures. Machine learning algorithms including support vector machine (SVM), random forest, k-nearest neighbors, Rpart, Xgboost, and Kriging algorithms are compared, with the Kriging algorithm achieving the best accuracies (r = 0.99 and R² = 0.98) and SVM achieving the second best. A total of 50,905 data points representing the complex multidimensional design space are predicted via the machine-learned models to benefit the future perovskite studies. In addition, the symbolic regression based on the genetic algorithms effectively and automatically designs hybrid descriptors that outperform the individual descriptors. This article highlights the machine learning and symbolic regression methods for designing stable and high-performance halide perovskite materials and serves as a platform for further experimental optimization of halide perovskite materials.

A high-efficiency and stable perovskite solar cell fabricated in ambient air using a polyaniline passivation layer

Over the past number of years, the power conversion efficiency of perovskite solar cells has remained at 25.5%, reflecting a respectable result for the general incorporation of organometallic trihalide perovskite solar cells. However, perovskite solar cells still suffer from long-term stability issues. Perovskite decomposes upon exposure to moisture, thermal, and UV-A light. Studies related to this context have remained ongoing. Recently, research was mainly conducted on the stability of perovskite against non-radiative recombination. This study improved a critical instability in perovskite solar cells arising from non-radiative recombination and UV-A light using a passivation layer. The passivation layer comprised a polyaniline (PANI) polymer as an interfacial modifier inserted between the active layer and the electron transport layer. Accordingly, the UV-A light did not reach the active layer and confined the Pb2+ ions at PANI passivation layer. This study optimized the perovskite solar cells by controlling the concentration, thickness and drying conditions of the PANI passivation layer. As a result, the efficiency of the perovskite solar cell was achieved 15.1% and showed over 84% maintain in efficiency in the ambient air for one month using the 65 nm PANI passivation layer.

MXene-Based Materials for Solar Cell Applications

MXenes are a class of two-dimensional nanomaterials with exceptional tailor-made properties, making them promising candidates for a wide variety of critical applications from energy systems, optics, electromagnetic interference shielding to those advanced sensors, and medical devices. Owing to its mechano-ceramic nature, MXenes have superior thermal, mechanical, and electrical properties. Recently, MXene-based materials are being extensively explored for solar cell applications wherein materials with superior sustainability, performance, and efficiency have been developed in demand to reduce the manufacturing cost of the present solar cell materials as well as enhance the productivity, efficiency, and performance of the MXene-based materials for solar energy harvesting. It is aimed in this review to study those MXenes employed in solar technologies, and in terms of the layout of the current paper, those 2D materials candidates used in solar cell applications are briefly reviewed and discussed, and then the fabrication methods are introduced. The key synthesis methods of MXenes, as well as the electrical, optical, and thermoelectric properties, are explained before those research efforts studying MXenes in solar cell materials are comprehensively discussed. It is believed that the use of MXene in solar technologies is in its infancy stage and many research efforts are yet to be performed on the current pitfalls to fill the existing voids.

The effect of heat-moisture treatment conditions on the structure properties and functionalities of potato starch

Potato starch was modified via heat-moisture treatment (HMT) under various reaction conditions. The effect of HMT on structural, physicochemical, and in vitro digestibility were investigated. HMT led to the rupture, adhesion and partial gelatinization, and agglomeration of the granules which surface became rougher, thereby increasing the particle size and resulting in the hollow structure located at the hilum of potato starch granules. XRD results showed an increased relative crystallinity and transformed crystalline structure from B-type to C-type with the extension of heat moisture treatment. FTIR spectroscopy results indicated that HMT might cause additional interactions between amylose-amylose, and/or amylose-amylopectin and/or amylopectin-amylopectin chains, which eventually leads to the increase of the mass of the carbonyl group and a hydroxyl group. HMT significantly decreased the peak viscosity, hold viscosity, and breakdown viscosity of starch, while the gelatinization temperature increased. The tHMT1, THMT100, and CHMT15 had the lowest content of RDS and there was no significant difference between the three samples, that is these three samples had the highest total content of SDS and RS.

Solvent Engineering of the Precursor Solution toward Large-Area Production of Perovskite Solar Cells

Solar cells based on emerging organic-inorganic hybrid perovskite materials have reached certified power conversion efficiency as high as 25.5%, showing great potential in the next generation of photovoltaics toward large-scale industrialization. The most competitive feature of perovskite solar cells (PSCs) is that the perovskite light absorber can be fabricated by a low-cost solution method. For the solution method, the characteristics of the solvent play a key role in determining the crystallization kinetics, growth orientation, and optoelectronic properties of the perovskite film. Although significant progress has been made in the field of solvent engineering in PSCs, it is still challenging for the solution method to sustainably produce industrial-scale PSCs for future commercialization applications. Herein, the advanced progress of solvent engineering of precursor solution in terms of coordination regulation and toxicity reduction is highlighted. The physical and chemical characteristics of different solvents in reducing the toxicity of the solvent system, regulating the coordination property of the precursor solution, controlling the film-forming process of the perovskite film, and adjusting the photovoltaic performance of the PSC are systematically discussed. Lastly, important perspectives on solvent engineering of the perovskite precursor solution toward future industrial production of high-performance PSCs are provided.

Ambient Fabrication of Organic-Inorganic Hybrid Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted significant attention in recent years due to their high-power conversion efficiency, simple fabrication, and low material cost. However, due to their high sensitivity to moisture and oxygen, high efficiency PSCs are mainly constructed in an inert environment. This has led to significant concerns associated with the long-term stability and manufacturing costs, which are some of the major limitations for the commercialization of this cutting-edge technology. Over the past few years, excellent progress in fabricating PSCs in ambient conditions has been made. These advancements have drawn considerable research interest in the photovoltaic community and shown great promise for the successful commercialization of efficient and stable PSCs. In this review, after providing an overview to the influence of an ambient fabrication environment on perovskite films, recent advances in fabricating efficient and stable PSCs in ambient conditions are discussed. Along with discussing the underlying challenges and limitations, the most appropriate strategies to fabricate efficient PSCs under ambient conditions are summarized along with multiple roadmaps to assist in the future development of this technology.

Good or evil: what is the role of water in crystallization of organometal halide perovskites?

Perovskite solar cells (PSCs) have the potential to become one of the most cost-efficient photovoltaic devices. However, current fabrication methods of PSCs still require strict environment control and ultrahigh purity chemicals, which could prevent their large-scale commercialization. To tackle this challenge, the role of water is the first to be thoroughly understood in a perovskite formation process. Until now, there is still controversy about whether water is harmful or beneficial for perovskite formation, not to mention exactly what role water plays therein. In this Focus article, we review recent studies on water involved chemical reactions, solvent interaction, intermediates, and crystal growth in the perovskite film formation process, in order to bring out a full picture about what water does in the perovskite formation process. As our current understanding stands, a suitable amount of water could be of help for growing high quality perovskite films due to the resultant formation of intermediates, such as MAPbI3·H2O, which facilitates the conversion from precursors to perovskites. However, too much water would induce the formation of relatively stable components, such as (MA)4PbI6·2H2O, which are left in the product-films as impurities resulting in degraded device performance. Continual efforts should be made to further understand and develop water-involved strategies for consistent PSC fabrication under ambient conditions.

Heavy Water Additive in Formamidinium: A Novel Approach to Enhance Perovskite Solar Cell Efficiency

Heavy water or deuterium oxide (D₂ O) comprises deuterium, a hydrogen isotope twice the mass of hydrogen. Contrary to the disadvantages of deuterated perovskites, such as shorter recombination lifetimes and lower/invariant efficiencies, the serendipitous effect of D₂ O as a beneficial solvent additive for enhancing the power conversion efficiency (PCE) of triple-A cation (cesium (Cs)/methylammonium (MA)/formaminidium (FA)) perovskite solar cells from ≈19.2% (reference) to 20.8% (using 1 vol% D₂ O) with higher stability is reported. Ultrafast optical spectroscopy confirms passivation of trap states, increased carrier recombination lifetimes, and enhanced charge carrier diffusion lengths in the deuterated samples. Fourier transform infrared spectroscopy and solid-state NMR spectroscopy validate the N-H₂ group as the preferential isotope exchange site. Furthermore, the NMR results reveal the induced alteration of the FA to MA ratio due to deuteration causes a widespread alteration to several dynamic processes that influence the photophysical properties. First-principles density functional theory calculations reveal a decrease in PbI₆ phonon frequencies in the deuterated perovskite lattice. This stabilizes the PbI₆ structures and weakens the electron-LO phonon (Fröhlich) coupling, yielding higher electron mobility. Importantly, these findings demonstrate that selective isotope exchange potentially opens new opportunities for tuning perovskite optoelectronic properties.

Role of Water in Suppressing Recombination Pathways in CH3NH3PbI3 Perovskite Solar Cells

Moisture degradation of halide perovskites is the Achilles heel of perovskite solar cells. A surprising revelation in 2014 about the beneficial effects of controlled humidity in enhancing device efficiencies overthrew established paradigms on perovskite solar cell fabrication. Despite the extensive studies on water additives in perovskite solar cell processing that followed, detailed understanding of the role of water from the photophysical perspective remains lacking; specifically, the interplay between the induced morphological effects and the intrinsic recombination pathways. Through ultrafast optical spectroscopy, we show that both the monomolecular and bimolecular recombination rate constants decrease by approximately 1 order with the addition of an optimal 1% H₂O by volume in CH₃NH₃PbI₃ as compared to the reference (without the H₂O additive). Correspondingly, the trap density reduces from 4.8 × 10¹⁷ cm^-3 (reference) to 3.2 × 10¹⁷ cm^-3 with 1% H₂O. We obtained an efficiency of 12.3% for the champion inverted CH₃NH₃PbI₃ perovskite solar cell (1% H₂O additive) as compared to the 10% efficiency for the reference cell. Increasing the H₂O content further is deleterious for the device. Trace amounts of H₂O afford the benefits of surface trap passivation and suppression of trap-mediated recombination, whereas higher concentrations result in a preferential dissolution of methylammonium iodide during fabrication that increases the trap density (MA vacancies). Importantly, our study reveals the effects of trace H₂O additives on the photophysical properties of CH₃NH₃PbI₃ films.

Synergistic interface and compositional engineering of inverted perovskite solar cells enables highly efficient and stable photovoltaic devices

Recently, interface and compositional engineering have been effective approaches in the field of perovskite solar cells (PSCs). In this work, the surface of the nickel oxide layer and perovskite composition are modified by poly[(9,9-bis(30-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN-P2) and deionized (DI) water, respectively, which result in a device with 20.5% efficiency and great stability.

Stable Efficiency Exceeding 20.6% for Inverted Perovskite Solar Cells through Polymer-Optimized PCBM Electron-Transport Layers

Fullerene derivative, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), is widely used as an electron-transport layer (ETL) in inverted perovskite solar cell (PSC). However, its low electron mobility, complexity in achieving quality film formation, and severe nonradiative recombination at perovskite/PCBM interface due to the large electron capture region, lead to lower efficiency for inverted PSCs compared to the normal structures. Herein, we demonstrate an effective and practical strategy to overcome these challenges. Conjugated n-type polymeric materials are mixed together with PCBM to form a homogeneous bulk-mixed (HBM) continuous film with high electron mobility and suitable energy level. HBM film is found to completely cap the perovskite surface to enhance the electron extraction. The critical electron capture radius of the HBM decreases to 12.52 nm from 14.89 nm of PCBM due to the large relative permittivity, resulting in reduced nonradiative recombination at perovskite/HBM interface. The efficiency of inverted PSCs with HBM ETLs exceeds 20.6% with a high fill factor of 0.82. Further, the stability of devices is improved owing to the high hydrophobicity of the HBM ETLs. Under ambient air condition after 45 days, the efficiency of inverted PSCs based on HBM remains 80% of the initial value. This is significantly higher than the control devices which retain only 48% of the initial value under similar aging conditions. We believe these breakthroughs in improving efficiency and stability of inverted PSCs will expedite their transition.

HPbI3 as a Bifunctional Additive for Morphology Control and Grain Boundary Passivation toward Efficient Planar Perovskite Solar Cells

One of the key aspects contributing to the rapid development of perovskite solar cells is to prepare high-quality perovskite films via morphology control and interface engineering. Here, we demonstrate that the additive HPbI₃ works effectively on both morphology control and grain boundary passivation of CH₃NH₃PbI_{3- x}Cl _x thin films. By inducing HPbI₃ to the crystal transformation process, high-quality perovskite films consisting of micro-sized grains with boundaries passivated by PbI₂ can be readily produced. The perovskite film obtained with HPbI₃ as the additive achieves a much longer carrier lifetime compared to the pristine perovskite film without the additive. Under the optimal HPbI₃ amount (5.0%), the average power conversion efficiency of the planar-heterojunction solar cells is increased by ∼24% to 17.42% from 14.09% for the device without the additive, and the champion efficiency reaches 18.59%. The devices without any encapsulation show impressive shelf stability, retaining more than 85% of the initial efficiency after being stored in ambient environment for over 40 days.

Room Temperature Processing of Inorganic Perovskite Films to Enable Flexible Solar Cells

Inorganic lead halide perovskite materials have attracted great attention recently due to their potential for greater thermal stability compared with hybrid organic perovskites. However, the high processing temperature to convert from the non-perovskite phase to the cubic perovskite phase in many of these systems has limited their application in flexible optoelectronic devices. Here, we report a room temperature processed inorganic perovskite solar cell (PSC) based on CsPbI2Br as the light harvesting layer. By combining this composition with key precursor solvents, we show that inorganic perovskite films can be prepared by the vacuum-assist method under room temperature conditions in air. Unencapsulated devices achieved power conversion efficiency up to 8.67% when measured under 1-sun irradiation. Exploiting this room temperature process, flexible inorganic PSCs based on an inorganic metal halide perovskite material are demonstrated.

Ultrathin Hole Extraction Layer for Efficient Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) incorporating poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT) as the hole transport/extraction layer have been broadly investigated in recent years. However, most PSCs which incorporate PEDOT as the hole transport layer (HTL) suffer from lower device performance stemming from reduced photocurrent and low open-circuit voltage around 0.95 V. Here, we report an ultrathin PEDOT layer as the HTL for efficient inverted structure PSCs. The transparency, conductivity, and resulting film morphology were studied and compared with traditional architectures and thicker PEDOT layers. The PSC device incorporating an ultrathin PEDOT layer shows significant improvement in short-circuit current density (J SC), open-circuit voltage (V OC), and power conversion efficiency. Because ultrathin PEDOT layers can be easily obtained by dilution, this study suggests a simple way to improve the PSC performance and provide a route to further reduce the fabrication complexity and cost of PSCs.