Sequential vacuum-evaporated perovskite solar cells with more than 24% efficiency

Strong Grain Boundary Passivation Effect of Coevaporated Dopants Enhances the Photoemission of Lead Halide Perovskites

Herein, we demonstrate that coevaporated dopants provide a means to passivate buried interfacial defects occurring at perovskite grain boundaries in evaporated perovskite thin films, thus giving rise to an enhanced photoluminescence. By means of an extensive photophysical characterization, we provide experimental evidence that indicate that the codopant acts mainly at the grain boundaries. They passivate interfacial traps and prevent the formation of photoinduced deep traps. On the other hand, the presence of an excessive amount of organic dopant can lead to a barrier for carrier diffusion. Hence, the passivation process demands a proper balance between the two effects. Our analysis on the role of the dopant, performed under different excitation regimes, permits evaluation of the performance of the material under conditions more adapted to photovoltaic or light emitting applications. In this context, the approach taken herein provides a screening method to evaluate the suitability of a passivating strategy prior to its incorporation into a device.

Scalable Fabrication of High-Performance Perovskite Solar Cell Modules by Mediated Vapor Deposition

Perovskite solar cells (PSCs) can enable renewable electricity generation at low levelized costs, subject to the invention of an economically feasible technology for their large-scale fabrication, like vapor deposition. This approach is effective for the fabrication of small area (<1 cm2) PSCs, but its scale-up to produce high-efficiency larger area modules has been limited by a severe imbalance between the vapor-solid reaction kinetics and the mass-transport of the volatile ammonium salt precursor. In this study, an amidine-based low-dimensional perovskite is introduced as an intermediate of the solid-vapor reaction to help resolve this limitation. This improves reaction pathway produces unique vertically monolithic grains with no detectable horizontal boundaries, which is used to produce 1.0 cm2 PSCs with an efficiency of 22.1%, as well as 12.5 and 48 cm2 modules delivering 21.1% and 20.1% efficiency, respectively. The modules retain ≈85% of their initial performance after 900 h of continuous operation (ISOS-L-1 protocol) and ≈100% after 2800 h of storage in an ambient environment (ISOS-D-1 protocol).

Post-Treating Grain Boundaries and Surface Defects by Long-Chain Polymer for Highly Efficient and Stable Perovskite Solar Cells

Grain boundaries (GBs) and surface defects within perovskite films are inherent challenges that affect the photovoltaic performance of perovskite solar cells  (PSCs. In this work, Nylon 11 (N11) is utilized, a long-chain polymer, for post-treating the GBs and surface defects within FAPbI3 films. The multifunctional groups of N11 exhibit unique passivation abilities, enabling self-regulation and selective correction of reverse-charged defects. Post-treating with N11 results in high-quality FAPbI3 films characterized by tight GBs and low surface defect density. Despite fabrication under full open-air conditions, the N11 post-treatment significantly enhances the power conversion efficiency (PCE) value of FAPbI3 PSCs, increasing it from the reference value of 21.89% to 23.54%. Importantly, the long alkyl chain present in N11 significantly enhances the humidity stability of the PSCs. Unencapsulated PSCs treated with N11 maintain 89% of their initial PCE after exposure to air with 30% relative humidity (RH) for 1000 h, demonstrating resilience to elevated humidity levels. This work highlights the substantial improvement in the photovoltaic performance of PSCs achieved through the post-treatment with N11.

The Promise and Challenges of Inverted Perovskite Solar Cells

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.

Achievements, challenges, and future prospects for industrialization of perovskite solar cells

In just over a decade, certified single-junction perovskite solar cells (PSCs) boast an impressive power conversion efficiency (PCE) of 26.1%. Such outstanding performance makes it highly viable for further development. Here, we have meticulously outlined challenges that arose during the industrialization of PSCs and proposed their corresponding solutions based on extensive research. We discussed the main challenges in this field including technological limitations, multi-scenario applications, sustainable development, etc. Mature photovoltaic solutions provide the perovskite community with invaluable insights for overcoming the challenges of industrialization. In the upcoming stages of PSCs advancement, it has become evident that addressing the challenges concerning long-term stability and sustainability is paramount. In this manner, we can facilitate a more effective integration of PSCs into our daily lives.

Surface Molecular Engineering for Fully Textured Perovskite/Silicon Tandem Solar Cells

Developing large-scale monolithic perovskite/silicon tandem devices based on industrial Czochralski silicon wafers will likely have to adopt double-side textured architecture, given their optical benefits and low manufacturing costs. However, the surface engineering strategies that are widely used in solution-processed perovskites to regulate the interface properties are not directly applicable to micrometric textures. Here, we devise a surface passivation strategy by dynamic spray coating (DSC) fluorinated thiophenethylammonium ligands, combining the advantages of providing conformal coverage and suppressing phase conversion on textured surfaces. From the viewpoint of molecular engineering, theoretical calculation and experimental results demonstrate that introducing trifluoromethyl group provide more effective surface passivation through strong interaction and energy alignment by forming a dipole layer. Consequently, the DSC treatment of this bifunctional molecule enables the tandem cells based on industrial silicon wafers to achieve a certified stabilized power conversion efficiency of 30.89 %. In addition, encapsulated devices display excellent operational stability by retaining over 97 % of their initial performance after 600 h continuous illumination.

Entropy-Driven Reversible Melting and Recrystallization of Layered Hybrid Perovskites

Typical layered 2D A2PbX4 (A: organic ammonium cation, X: Br, I) perovskites undergo irreversible decomposition at high temperatures. Can they be designed to melt at lower temperatures without decomposition? Which thermodynamic parameter drive the melting of layered perovskites? These questions are addressed by considering the melt of A2PbX4 as a mixture of ions (like ionic liquids), and hypothesized that the increase in the structural entropy of fusion (ΔSfus) will be the driving force to decrease their melting temperature. Then to increase structural ΔSfus, A-site cations are designed that are rigid in the solid crystal, and become flexible in the molten state. Different tail groups in the A-site cations form hydrogen-, halogen- and even covalent bonding-interactions, making the cation-layer rigid in the solid form. Additionally, the rotation of ─NH3 + head group is suppressed by replacing ─H with ─CH3, further enhancing the rigidity. Six A2PbX4 crystals with high ΔSfus and low melting temperatures are prepared using this approach. For example, [I-(CH2)3-NH2(CH3)]2PbI4 reversibly melts at 388 K (decomposition temperature 500 K), and then recrystallizes back upon cooling. Consequently, melt-pressed films are grown demonstrating the solvent- and vacuum-free perovskite films for future optoelectronic devices.

Fusing Science with Industry: Perovskite Photovoltaics Moving Rapidly into Industrialization

The organic-inorganic lead halide per materials have emerged as highly promising contenders in the field of photovoltaic technology, offering exceptional efficiency and cost-effectiveness. The commercialization of perovskite photovoltaics hinges on successfully transitioning from lab-scale perovskite solar cells to large-scale perovskite solar modules (PSMs). However, the efficiency of PSMs significantly diminishes with increasing device area, impeding commercial viability. Central to achieving high-efficiency PSMs is fabricating uniform functional films and optimizing interfaces to minimize energy loss. This review sheds light on the path toward large-scale PSMs, emphasizing the pivotal role of integrating cutting-edge scientific research with industrial technology. By exploring scalable deposition techniques and optimization strategies, the advancements and challenges in fabricating large-area perovskite films are revealed. Subsequently, the architecture and contact materials of PSMs are delved while addressing pertinent interface issues. Crucially, efficiency loss during scale-up and stability risks encountered by PSMs is analyzed. Furthermore, the advancements in industrial efforts toward perovskite commercialization are highlighted, emphasizing the perspective of PSMs in revolutionizing renewable energy. By highlighting the scientific and technical challenges in developing PSMs, the importance of combining science and industry to drive their industrialization and pave the way for future advancements is stressed.

Controlled Crystallization and Enhanced Performance of γ-CsPbI3 Perovskite Through Methylammonium Iodide-Assisted Coevaporation

Cesium lead triiodide (CsPbI3) perovskites have garnered significant attention owing to their suitable bandgap for tandem silicon substrates and excellent chemical stability. However, γ-CsPbI3 prepared via low-temperature co-evaporation is limited by a narrow black phase processing window and random crystal orientation, hindering its optoelectronic performance and industrial applications. This study introduced trace amounts of methylammonium iodide (MAI) into the co-evaporation system, enhancing the crystallization process, promoting columnar grain growth, and stabilizing the γ-phase perovskite, resulting in films with improved structural integrity and reduced defect density. The optimal Pb/Cs ratio for achieving the best photoelectric performance shifted from 1:1 to 1.1:1 in the presence of MAI. Additionally, the incorporation of MAI allowed for more efficient longitudinal carrier transport, as evidenced by the enhanced photoluminescence (PL) intensity. The bandgap of CsPbI3 remained approximately at 1.7 eV before the δ-phase transition, ensuring suitability for photovoltaic applications. Ultimately, a photovoltaic device with 12% efficiency is achieved in the p-i-n structure without additional post-annealing of the CsPbI3 perovskite films, demonstrating the practical benefits of MAI incorporation.

Controlled Crystal Growth of All-Inorganic CsPbI2Br via Sequential Vacuum Deposition for Efficient Perovskite Solar Cells

Vacuum deposition of perovskites is a promising method for scale-up fabrication and uniform film growth. However, improvements in the photovoltaic performance of perovskites are limited by the fabrication of perovskite films, which are not optimized for high device efficiency in the vacuum evaporation process. Herein, we fabricate CsPbI2Br perovskite with high crystallinity and larger grain size by controlling the deposition sequence between PbI2 and CsBr. The nucleation barrier for perovskite formation is significantly lowered by first evaporating CsBr and then PbI2 (CsBr-PbI2), followed by the sequential evaporation of multiple layers. The results show that the reduced Gibbs free energy of CsBr-PbI2, compared with that of PbI2-CsBr, accelerates perovskite formation, resulting in larger grain size and reduced defect density. Furthermore, surface-modified homojunction perovskites are fabricated to efficiently extract charge carriers and enhance the efficiency of perovskite solar cells (PeSCs) by modulating the final PbI2 thickness before thermal annealing. Using these strategies, the best PeSC exhibits a power conversion efficiency of 13.41% for a small area (0.135 cm2), the highest value among sequential thermal deposition inorganic PeSCs, and 11.10% for a large area PeSC (1 cm2). This study presents an effective way to understand the crystal growth of thermally deposited perovskites and improve their performance in optoelectronic devices.

Composition Dictates Octahedral Tilt and Photostability in Halide Perovskites

Halide perovskites are excellent candidate materials for use in solar cell, LED, and detector devices, in part because their composition can be tuned to achieve ideal optoelectronic properties. Empirical efficiency optimization has led the field toward compositions rich in FA (formamidinium) on the A-site and I on the X-site, with additional small amounts of MA (methylammonium) or Cs A-site cations and Br X-site anions. However, it is not clear how and why the specific compositions of alloyed, that is, mixed component, halide perovskites relate to photo-stability of the materials. Here, this work combines synchrotron grazing incidence wide-angle X-ray scattering, photoluminescence, high-resolution scanning electron diffraction measurements and theoretical modelling to reveal the links between material structure and photostability. Namely, this work finds that increased octahedral titling leads to improved photo-stability that is correlated with lower densities of performance-harming hexagonal polytype impurities. These results uncover the structural signatures underpinning photo-stability and can therefore be used to make targeted changes to halide perovskites, bettering the commercial prospects of technologies based on these materials.

Electron Spectroscopy and Microscopy: A Window into the Surface Electronic Properties of Polycrystalline Metal Halide Perovskites

In the past years, an increasing number of experimental techniques have emerged to address the need to unveil the chemical, structural, and electronic properties of perovskite thin films with high vertical and lateral spatial resolutions. One of these is angle-resolved photoemission electron spectroscopy which can provide direct access to the electronic band structure of perovskites, with the aim of overcoming elusive and controversial information due to the complex data interpretation of purely optical spectroscopic techniques. This perspective looks at the information that can be gleaned from the direct measurement of the electronic band structure of single crystal perovskites and the challenges that remain to be overcame to extend this technique to heterogeneous polycrystalline metal halide perovskites.

Cl alloying improves thermal stability and increases luminescence in iodine-rich inorganic perovskites

The inorganic perovskite CsPbI3 shows promising photophysical properties for a range of potential optoelectronic applications but is metastable at room temperature. To address this, Br can be alloyed into the X-site to create compositions such as CsPbI2Br that are stable at room temperature but have bandgaps >1.9 eV - severely limiting solar applications. Herein, in an effort to achieve phase stable films with bandgaps <1.85 eV, we investigate alloying chlorine into iodine-rich triple-halide CsPb(I0.8Br0.2-x Cl x )3 with 0 < x < 0.1. We show that partial substitution of iodine with bromine and chlorine provides a path to maintain broadband terrestrial absorption while improving upon the perovskite phase stability due to chlorine's smaller size and larger ionization potential than bromine. At moderate Cl loading up to ≈5%, X-ray diffraction reveals an increasingly smaller orthorhombic unit cell, suggesting chlorine incorporation into the lattice. Most notably, this Cl incorporation is accompanied by a significant enhancement over Cl-free controls in the duration of black-phase stability of up to 7× at elevated temperatures. Additionally, we observe up to 5× increased steady state photoluminescence intensity (PL), along with a small blue-shift. In contrast, at high loading (≈10%), Cl accumulates in a second phase that is visible at grain boundaries via synchrotron fluorescence microscopy and negatively impacts the perovskite phase stability. Thus, replacing small fractions of bromine for chlorine in the iodine-rich inorganic perovskite lattice results in distinct improvement thermal stability and optoelectronic quality while minimally impacting the bandgap.

Ordered Perovskite Structure with Functional Units for High Performance and Stable Solar Cells

Ion migration is one of the most critical challenges that affects the stability of metal-halide perovskite solar cells (PSCs). However, the current arsenal of available strategies for solving this issue is limited. Here, novel perovskite active layers following the concept of ordered structures with functional units (OSFU) to intrinsically suppress ion migration, in which a three-dimensional (3D) perovskite layer is deposited by vapor deposition for light absorption and a 2D layer is deposited by solution process for ion inhibition, are constructed. As a promising result, the activation energy of ion migration increases from 0.36 eV for the conventional perovskite to 0.54 eV for the OSFU perovskite. These devices exhibit substantially enhanced operational stability in comparison with the conventional ones, retaining >85% of their initial efficiencies after 1200 h under ISOS-L-1. Moreover, the OSFU devices show negligible fatigue behavior with a robust performance under light/dark cycling aging test (ISOS-LC-1 protocol), which demonstrates the promising application of functional motif theory in this field.

Solvent-free preparation and thermocompression self-assembly: an exploration of performance improvement strategies for perovskite solar cells

Perovskite solar cells (PSCs) exhibit sufficient technological efficiency and economic competitiveness. However, their poor stability and scalability are crucial factors limiting their rapid development. Therefore, achieving both high efficiency and good stability is an urgent challenge. In addition, the preparation methods for PSCs are currently limited to laboratory-scale methods, so their commercialization requires further research. Effective packaging technology is essential to protect the PSCs from degradation by external environmental factors and ensure their long-term stability. The industrialization of PSCs is also inseparable from the preparation technology of perovskite thin films. This review discusses the solvent-free preparation of PSCs, shedding light on the factors that affect PSC performance and strategies for performance enhancement. Furthermore, this review analyzes the existing simulation techniques that have contributed to a better understanding of the interfacial evolution of PSCs during the packaging process. Finally, the current challenges and possible solutions are highlighted, providing insights to facilitate the development of highly efficient and stable PSC modules to promote their widespread application.

Efficient and Stable Inverted Perovskite Solar Modules Enabled by Solid-Liquid Two-Step Film Formation

A considerable efficiency gap exists between large-area perovskite solar modules and small-area perovskite solar cells. The control of forming uniform and large-area film and perovskite crystallization is still the main obstacle restricting the efficiency of PSMs. In this work, we adopted a solid-liquid two-step film formation technique, which involved the evaporation of a lead iodide film and blade coating of an organic ammonium halide solution to prepare perovskite films. This method possesses the advantages of integrating vapor deposition and solution methods, which could apply to substrates with different roughness and avoid using toxic solvents to achieve a more uniform, large-area perovskite film. Furthermore, modification of the NiOx/perovskite buried interface and introduction of Urea additives were utilized to reduce interface recombination and regulate perovskite crystallization. As a result, a large-area perovskite film possessing larger grains, fewer pinholes, and reduced defects could be achieved. The inverted PSM with an active area of 61.56 cm2 (10 × 10 cm2 substrate) achieved a champion power conversion efficiency of 20.56% and significantly improved stability. This method suggests an innovative approach to resolving the uniformity issue associated with large-area film fabrication.

Vacuum-Processed Propylene Urea Additive: A Novel Approach for Controlling the Growth of CH3NH3PbI3 Crystals in All Vacuum-Processed Perovskite Solar Cells

In this study, we present a novel method for controlling the growth of perovskite crystals in the vacuum thermal evaporation process by utilizing a vacuum-processable additive, propylene urea (PU). By coevaporation of perovskite precursors with PU to form the perovskite layer, PU, acting as a Lewis base additive, retards the direct reaction between the perovskite precursors. This facilitates a larger domain size and reduced defect density. Following the removal of the residual additive, the perovskite layer, exhibiting improved crystallinity, demonstrates reduced charge recombination, as confirmed by a time-resolved microwave conductivity analysis. Consequently, there is a notable enhancement in open-circuit voltage and power conversion efficiency, increasing from 1.05 to 1.15 V and from 17.17 to 18.31%, respectively. The incorporation of a vacuum-processable and removable Lewis base additive into the fabrication of vacuum-processed perovskite solar cells offers new avenues for optimizing these devices.

Thermally Evaporated Metal Halide Perovskites and Their Analogues: Film Fabrication, Applications and Beyond

Metal halide perovskites emerge as promising semiconductors for optoelectronic devices due to ease of fabrication, attractive photophysical properties, their low cost, highly tunable material properties, and high performance. High-quality thin films of metal halide perovskites are the basis of most of these applications including solar cells, light-emitting diodes, photodetectors, and electronic memristors. A typical fabrication method for perovskite thin films is the solution method, which has several limitations in device reproducibility, adverse environmental impact, and utilization of raw materials. Thermal evaporation holds great promise in addressing these bottlenecks in fabricating high-quality halide perovskite thin films. It also has high compatibility with mass-production platforms that are well-established in industries. This review first introduces the basics of the thermal evaporation method with a particular focus on the critical parameters influencing the thin film deposition. The research progress of the fabrication of metal halide perovskite thin films is further summarized by different thermal evaporation approaches and their applications in solar cells and other optoelectronic devices. Finally, research challenges and future opportunities for both fundamental research and commercialization are discussed.

Doping with KBr to Achieve High-Performance CsPbBr3 Semitransparent Perovskite Solar Cells

Wide-bandgap semitransparent perovskite photovoltaics are emerging as one of the ideal candidates for building-integrated photovoltaics (BIPV). However, surface defects in inorganic CsPbBr3 perovskite prepared by vapor deposition severely limit the optoelectronic performance of perovskite solar cells. To address this issue, a strategy of doping a trace amount of KBr into perovskite by vapor deposition is adopted, effectively improving the quality of the film, reducing surface defect concentration, and enhancing the transportation and extraction of charge carriers. Simultaneously, fully physical vapor deposition technology is employed to fabricate perovskite solar cells with an average visible light transmittance of 44%. These devices exhibited an ultrahigh open-circuit voltage of 1.55 V and a superior power conversion efficiency (PCE) of 7.28%, demonstrating excellent moisture and heat resistance. Moreover, the corresponding 5 cm × 5 cm modules achieve a PCE of 5.35% with great thermal insulation capability. This work provides an approach for fabricating highly efficient all-inorganic perovskite solar cells with high average visible light transmittance, demonstrating new insights into their application in building-integrated photovoltaics.

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics

All-perovskite tandem solar cells are attracting considerable interest in photovoltaics research, owing to their potential to surpass the theoretical efficiency limit of single-junction cells, in a cost-effective sustainable manner. Thanks to the bandgap-bowing effect, mixed tin-lead (Sn-Pb) perovskites possess a close to ideal narrow bandgap for constructing tandem cells, matched with wide-bandgap neat lead-based counterparts. The performance of all-perovskite tandems, however, has yet to reach its efficiency potential. One of the main obstacles that need to be overcome is the─oftentimes─low quality of the mixed Sn-Pb perovskite films, largely caused by the facile oxidation of Sn(II) to Sn(IV), as well as the difficult-to-control film crystallization dynamics. Additional detrimental imperfections are introduced in the perovskite thin film, particularly at its vulnerable surfaces, including the top and bottom interfaces as well as the grain boundaries. Due to these issues, the resultant device performance is distinctly far lower than their theoretically achievable maximum efficiency. Robust modifications and improvements to the surfaces of mixed Sn-Pb perovskite films are therefore critical for the advancement of the field. This Review describes the origins of imperfections in thin films and covers efforts made so far toward reaching a better understanding of mixed Sn-Pb perovskites, in particular with respect to surface modifications that improved the efficiency and stability of the narrow bandgap solar cells. In addition, we also outline the important issues of integrating the narrow bandgap subcells for achieving reliable and efficient all-perovskite double- and multi-junction tandems. Future work should focus on the characterization and visualization of the specific surface defects, as well as tracking their evolution under different external stimuli, guiding in turn the processing for efficient and stable single-junction and tandem solar cell devices.

Rational Design of New Small Derivatives of 2,2'-Bithiophene as Hole Transport Material for Perovskite Solar Cells

Using Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT) methods, this inquiry theoretically examines seven novel hole-transport materials (HTMs) namely DFBT1, DFBT2, DFBT3, DFBT4, DFBT5, DFBT6, and DFBT7 based on the 2,2'bithiophene core for future use as HTMs for perovskite solar cells (PSCs). The model molecule has been modified through substituting the end groups situated on the diphenylamine moieties with a tow acceptor bridged by thiophene, this modification was performed to test the impact of the π-bridge and acceptor on the electronic, photophysical, and photovoltaic properties of the newly created molecules. DFBT1 - DFBT7 displayed a lower band gap (1.49 eV to 2.69 eV) than the model molecule (3.63 eV). Additionally, the newly engineered molecules presented a greater λmax ranging from 393.07 nm to 541.02 nm in dimethylformamide solvent, as compared to the model molecule (380.61 nm). The PCEs of all newly designed molecules (22.42% to 29.21%) were high compared with the reference molecule (19.62%). Thus, this study showed that all seven newly small molecules were excellent candidates for a novel PSC.

Modulating the Distribution of Formamidinium Iodide by Ultrahigh Humidity Treatment Strategy for High-Quality Sequential Vapor Deposited Perovskite

The quality of two-step processed perovskites is significantly influenced by the distribution of organic amine salts. Especially, modulating the distribution of organic amine salts remains a grand challenge for sequential vapor-deposited perovskites due to the blocking effect of bottom compact PbI2. Herein, an ultrahigh humidity treatment strategy is developed to facilitate the diffusion of formamidinium iodide (FAI) from the top surface to the buried bottom interface on the sequential vapor-deposited bilayer structure. Both experimental and theoretical investigations elucidate the mechanism that moisture helps to i) create FAI diffusion channels by inducing a phase transition from α- to δ-phase in the perovskite, and ii) enhance the diffusivity of FAI by forming hydrogen bonds. This ultrahigh humidity treatment strategy enables the formation of a desired homogeneous and high-quality α-phase after annealing. As a result, a champion efficiency of 22.0% is achieved and 97.5% of its initial performance is maintained after aging for 1050 h under ambient air with a relative humidity of up to 80%. This FAI diffusion strategy provides new insights into the reproducible, scalable, and high-performance sequential vapor-deposited perovskite solar cells.

Asymmetric Triphenylethylene-Based Hole Transporting Materials for Highly Efficient Perovskite Solar Cells

Molecular hole-transporting materials (HTMs) having triphenylethylene central core were designed, synthesized, and employed in perovskite solar cell (PSC) devices. The synthesized HTM derivatives were obtained in a two- or three-step synthetic procedure, and their characteristics were analyzed by various thermoanalytical, optical, photophysical, and photovoltaic techniques. The most efficient PSC device recorded a 23.43% power conversion efficiency. Furthermore, the longevity of the device employing V1509 HTM surpassed that of PSC with state-of-art spiro-OMeTAD as the reference HTM.

Functional-Group-Induced Single Quantum Well Dion-Jacobson 2D Perovskite for Efficient and Stable Inverted Perovskite Solar Cells

In two-dimensional/three-dimensional (2D/3D) perovskite heterostructure, randomly distributed multiple quantum wells (QW) 2D perovskites are frequently generated, which are detrimental to carrier transport and structural stability. Here, the high quality 2D/3D perovskite heterostructure is constructed by fabricating functional-group-induced single QW Dion-Jacobson (DJ) 2D perovskites. The utilization of ─OCH3 in the precursor solution facilitates the formation of colloidal particles with uniform size, resulting in the production of a pure 2D DJ perovskite with an n value of 3. This strategy facilitates the improvement of 3D structural stability and expedites carrier transport. The resultant devices accomplish a power conversion efficiency of 25.26% (certified 25.04%) and 23.56% at a larger area (1 cm2 ) with negligible hysteresis. The devices maintain >96% and >89% of their initial efficiency after continuous maximum power point tracking under simulated AM1.5 illumination for 1300 h and under damp-heat conditions (85 °C and 85% RH) for 1010 h, respectively.

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.

Pathways toward commercial perovskite/silicon tandem photovoltaics

Perovskite/silicon tandem solar cells offer a promising route to increase the power conversion efficiency of crystalline silicon (c-Si) solar cells beyond the theoretical single-junction limitations at an affordable cost. In the past decade, progress has been made toward the fabrication of highly efficient laboratory-scale tandems through a range of vacuum- and solution-based perovskite processing technologies onto various types of c-Si bottom cells. However, to become a commercial reality, the transition from laboratory to industrial fabrication will require appropriate, scalable input materials and manufacturing processes. In addition, perovskite/silicon tandem research needs to increasingly focus on stability, reliability, throughput of cell production and characterization, cell-to-module integration, and accurate field-performance prediction and evaluation. This Review discusses these aspects in view of contemporary solar cell manufacturing, offers insights into the possible pathways toward commercial perovskite/silicon tandem photovoltaics, and highlights research opportunities to realize this goal.

High-Efficiency and Emission-Tunable Inorganic Blue Perovskite Light-Emitting Diodes Based on Vacuum Deposition

The fabrication of perovskite light-emitting diodes (PeLEDs) with vacuum deposition shows great potential and commercial value in realizing large-area display panel manufacturing. However, the electroluminescence (EL) performance of vacuum-deposited PeLEDs still lags behind the counterparts fabricated by solution process, especially in the field of blue PeLEDs. Here, the fabrication of high-quality CsPbBr3- x Clx film through tri-source co-evaporation is reported to achieve high photoluminescence quantum yield (PLQY). Compared with the conventional traditional dual-source co-evaporation, the tri-source co-evaporation method allows for freely adjustable elemental ratios, enabling the introduction of the lattice-matched Cs4 Pb(Br/Cl)6 phase with the quantum-limited effect into the inorganic CsPb(Br/Cl)3 emitter. By adjusting the phase distribution, the surface defects of the emitter can be effectively reduced, leading to better blue emission and film quality. Further, the effects of Cs/Pb ratio and Br/Cl ratio on the PLQY and carrier recombination dynamics of perovskite films are investigated. By optimizing the deposition rate of each precursor source, spectrally stable blue PeLEDs are achieved with tunable emission ranging from 468 to 488 nm. Particularly, the PeLEDs with an EL peak at 488 nm show an external quantum efficiency (EQE) of 4.56%, which is the highest EQE value for mixed-halide PeLEDs fabricated by vacuum deposition.

Recent Advances in Patterning Strategies for Full-Color Perovskite Light-Emitting Diodes

Metal halide perovskites have emerged as promising light-emitting materials for next-generation displays owing to their remarkable material characteristics including broad color tunability, pure color emission with remarkably narrow bandwidths, high quantum yield, and solution processability. Despite recent advances have pushed the luminance efficiency of monochromic perovskite light-emitting diodes (PeLEDs) to their theoretical limits, their current fabrication using the spin-coating process poses limitations for fabrication of full-color displays. To integrate PeLEDs into full-color display panels, it is crucial to pattern red-green-blue (RGB) perovskite pixels, while mitigating issues such as cross-contamination and reductions in luminous efficiency. Herein, we present state-of-the-art patterning technologies for the development of full-color PeLEDs. First, we highlight recent advances in the development of efficient PeLEDs. Second, we discuss various patterning techniques of MPHs (i.e., photolithography, inkjet printing, electron beam lithography and laser-assisted lithography, electrohydrodynamic jet printing, thermal evaporation, and transfer printing) for fabrication of RGB pixelated displays. These patterning techniques can be classified into two distinct approaches: in situ crystallization patterning using perovskite precursors and patterning of colloidal perovskite nanocrystals. This review highlights advancements and limitations in patterning techniques for PeLEDs, paving the way for integrating PeLEDs into full-color panels.

Fast Coevaporation of 1 μm Thick Perovskite Solar Cells

Coevaporation of perovskite films allows for a fine control over the material stoichiometry and thickness but is typically slow, leading to several-hour processes to obtain thick films required for photovoltaic applications. In this work, we demonstrate the coevaporation of perovskite layers using faster deposition rates, obtaining 1 μm thick films in approximately 50 min. We observed distinct structural properties and obtained devices with efficiency exceeding 19%, demonstrating the relevance of this deposition process from a material perspective and also in view of potential industrialization.

Achieving High Fill Factor in Efficient P-i-N Perovskite Solar Cells

Lead halide perovskite solar cells (PSCs) have made unprecedented progress, exhibiting great potential for commercialization. Among them, inverted p-i-n PSCs provide outstanding compatibility with flexible substrates, more importantly, with silicon (Si) bottom devices for higher efficiency perovskite-Si tandem solar cells. However, even with recently obtained efficiency over 25%, the investigation of inverted p-i-n PSCs is still behind the n-i-p counterpart so far. Recent progress has demonstrated that the fill factor (FF) in inverted PSCs currently still underperforms relative to open-circuit voltage and short-circuit current density, which requires an in-depth understanding of the mechanism and further research. In this review article, the recent advancements in high FF inverted PSCs by adopting the approaches of interfacial optimization, precursor engineering as well as fabrication techniques to minimize undesirable recombination are summarized. Insufficient carrier extraction and transport efficiency are found to be the main factors that hinder the current FF of inverted PSCs. In addition, insights into the main factors limiting FF and strategies for minimizing series resistance in inverted PSCs are presented. The continuous efforts dedicated to the FF of high-performance inverted devices may pave the way toward commercial applications of PSCs in the near future.

Grain Boundary Elimination via Recrystallization-Assisted Vapor Deposition for Efficient and Stable Perovskite Solar Cells and Modules

Vapor deposition is a promising technology for the mass production of perovskite solar cells. However, the efficiencies of solar cells and modules based on vapor-deposited perovskites are significantly lower than those fabricated using the solution method. Emerging evidence suggests that large defects are generated during vapor deposition owing to a specific top-down crystallization mechanism. Herein, a hybrid vapor deposition method combined with solvent-assisted recrystallization for fabricating high-quality large-area perovskite films with low defect densities is presented. It is demonstrated that an intermediate phase can be formed at the grain boundaries, which induces the secondary growth of small grains into large ones. Consequently, perovskite films with substantially reduced grain boundaries and defect densities are fabricated. Results of temperature-dependent charge-carrier dynamics show that the proposed method successfully suppresses all recombination reactions. Champion efficiencies of 21.9% for small-area (0.16 cm2 ) cells and 19.9% for large-area (10.0 cm2 ) solar modules under AM 1.5 G irradiation are achieved. Moreover, the modules exhibit high operational stability, i.e., they retain >92% of their initial efficiencies after 200 h of continuous operation.

A Templating Approach to Controlling the Growth of Coevaporated Halide Perovskites

Metal halide perovskite semiconductors have shown significant potential for use in photovoltaic (PV) devices. While fabrication of perovskite thin films can be achieved through a variety of techniques, thermal vapor deposition is particularly promising, allowing for high-throughput fabrication. However, the ability to control the nucleation and growth of these materials, particularly at the charge-transport layer/perovskite interface, is critical to unlocking the full potential of vapor-deposited perovskite PV. In this study, we explore the use of a templating layer to control the growth of coevaporated perovskite films and find that such templating leads to highly oriented films with identical morphology, crystal structure, and optoelectronic properties independent of the underlying layers. Solar cells incorporating templated FA0.9Cs0.1PbI3-xClx show marked improvements with steady-state power conversion efficiency over 19.8%. Our findings provide a straightforward and reproducible method of controlling the charge-transport layer/coevaporated perovskite interface, further clearing the path toward large-scale fabrication of efficient PV devices.

Vacuum Deposited Perovskites with a Controllable Crystal Orientation

The preferential orientation of the perovskite (PVK) is typically accomplished by manipulation of the mixed cation/halide composition of the solution used for wet processing. However, for PVKs grown by thermal evaporation, this has been rarely addressed. It is unclear how variation in crystal orientation affects the optoelectronic properties of thermally evaporated films, including the charge carrier mobility, lifetime, and trap densities. In this study, we use different intermediate annealing temperatures Tinter between two sequential evaporation cycles to control the Cs0.15FA0.85PbI2.85Br0.15 orientation of the final PVK layer. XRD and 2D-XRD measurements reveal that when using no intermediate annealing primarily the (110) orientation is obtained, while when using Tinter = 100 °C a nearly isotropic orientation is found. Most interestingly for Tinter > 130 °C a highly oriented PVK (100) is formed. We found that although bulk electronic properties like photoconductivity are independent of the preferential orientation, surface related properties differ substantially. The highly oriented PVK (100) exhibits improved photoluminescence in terms of yield and lifetime. In addition, high spatial resolution mappings of the contact potential difference (CPD) as measured by KPFM for the highly oriented PVK show a more homogeneous surface potential distribution than those of the nonoriented PVK. These observations suggest that a highly oriented growth of thermally evaporated PVK is preferred to improve the charge extraction at the device level.

Self-Assembled Monolayers of Bi-Functionalized Porphyrins: A Novel Class of Hole-Layer-Coordinating Perovskites and Indium Tin Oxide in Inverted Solar Cells

Self-assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis of a new series of carboxylic acid-functionalized porphyrin derivatives, namely AC-1, AC-3, and AC-5, and present, for the first time, a strategy to exploit the large π-moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron-rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects. Comprehensive spectroscopic and dynamic studies demonstrate that the double-anchored AC-3 and AC-5 enhance SAMs on ITO, passivate the perovskite layer, and function as conduits to facilitate hole transfer, thus significantly boosting the performance of PSCs. The champion inverted PSC employing AC-5 SAM achieves an impressive solar efficiency of 23.19 % with a high fill factor of 84.05 %. This work presents a novel molecular engineering strategy for functionalizing SAMs to tune the energy levels, molecular dipoles, packing orientations to achieve stable and efficient solar performance. Importantly, our comprehensive investigation has unraveled the associated mechanisms, offering valuable insights for future advancements in PSCs.

Buried-Interface Engineering of Conformal 2D/3D Perovskite Heterojunction for Efficient Perovskite/Silicon Tandem Solar Cells on Industrially Textured Silicon

Exploring strategies to control the crystallization and modulate interfacial properties for high-quality perovskite film on industry-relevant textured crystalline silicon solar cells is highly valued in the perovskite/silicon tandem photovoltaics community. The formation of a 2D/3D perovskite heterojunction is widely employed to passivate defects and suppress ion migration in the film surface of perovskite solar cells. However, realizing solution-processed heterostructures at the buried interface faces solvent incompatibilities with the challenge of underlying-layer disruption, and texture incompatibilities with the challenge of uneven coverage. Here, a hybrid two-step deposition method is used to prepare robust 2D perovskites with cross-linkable ligands underneath the 3D perovskite. This structurally coherent interlayer benefits by way of preferred crystal growth of strain-free and uniform upper perovskite, inhibits interfacial defect-induced instability and recombination, and promotes charge-carrier extraction with ideal energy-level alignment. The broad applicability of the bottom-contact heterostructure for different textured substrates with conformal coverage and various precursor solutions with intact properties free of erosion are demonstrated. With this buried interface engineering strategy, the resulting perovskite/silicon tandem cells, based on industrially textured Czochralski (CZ) silicon, achieve a certified efficiency of 28.4% (1.0 cm2 ), while retaining 89% of the initial PCE after over 1000 h operation.

Reaction Dynamics of C(NH2)3SnI3 Formation from Vacuum-Deposited C(NH2)3I and SnI2 Bilayer Thin Films Investigated by In Situ Infrared Multiple-Angle Incidence-Resolved Spectroscopy

Understanding the formation process of organic-inorganic halide perovskite (OIHP) thin films is important for the fabrication of high-quality thin films, which, in turn, are crucial for achieving high-performance devices. To address this challenge, we developed an in situ system of infrared multiple-angle incidence-resolved spectroscopy (IR-MAIRS) combined with a vacuum deposition system. "Orientation-free" isotropic spectra constructed from IR-MAIRS spectra enable us to perform quantitative analysis of the formation process of C(NH2)3SnI3 (GASnI3) thin films from unreacted C(NH2)3I (guanidine hydroiodide (GAI))/SnI2 bilayer structures predeposited in a vacuum. The analysis of the dependence of the GASnI3 formation rate on the reaction temperature using the Avrami model has revealed that a diffusion-controlled reaction process of GAI and SnI2 governs the formation kinetics. The present study points to the usefulness of in situ IR-MAIRS analysis in understanding the growth mechanisms of vacuum-deposited OIHP thin films and hence the potential to accelerate the development of vacuum processes for the fabrication of high-quality OIHP thin films.

Effect of steric hindrance and number of substituents on the transfer and interface properties of Y-shaped hole-transporting materials for perovskite solar cells

Alkyl sulfoxide groups were introduced into the branch chain terminals of a hole-transporting material (HTM) Z34 with different numbers and positions to design four new Y-shaped HTMs: ZT1, ZT2, ZT3 and ZT4. The effects of steric hindrance and number of substituents on the transfer and interface properties of the Y-shaped HTMs were investigated theoretically. Calculations reveal that the introduction of alkyl sulfoxide increases the distribution of intramolecular holes and orbital overlap between the HOMOs of the dimers. The electronic coupling was greatly improved owing to the increased distribution of holes and orbital overlap. ZT1 shows small steric hindrance when one alkyl sulfoxide is introduced into the top branch chain, which leads to translation π-π stacking. ZT2 and ZT4 show slightly greater steric hindrance when two or four alkyl sulfoxide groups are introduced into the side branch chains, which leads to face-to-face stacking. While ZT3 shows large steric hindrance when three alkyl sulfoxide groups are introduced into the top and side branch chains, which causes head-to-head stacking. With the increase in number of alkyl sulfoxide groups, the steric hindrance of the molecule increases and the hole mobility decreases. ZT1 achieves the highest hole mobility (2.63 × 10-2 m2 V-1 s-1) that is two orders of magnitude higher than that of Z34 (1.36 × 10-4 m2 V-1 s-1) owing to the optimal balance between the number of alkyl sulfoxide groups and steric hindrance. The HTM/CH3NH3PbI3 adsorbed system was also simulated to characterize the interface properties. Enhanced interface interaction was achieved in the HTM/perovskite systems of ZT2 and ZT3. The orbital distribution of the HTM/perovskite cluster indicates that the new HTMs can promote hole migration and prevent internal electron-hole recombination. The present work not only evaluates the reliable relationship between the structure and properties of new HTMs, but also provides a valuable design strategy for efficient Y-shaped HTMs.

Synergy of 3D and 2D Perovskites for Durable, Efficient Solar Cells and Beyond

Three-dimensional (3D) organic-inorganic lead halide perovskites have emerged in the past few years as a promising material for low-cost, high-efficiency optoelectronic devices. Spurred by this recent interest, several subclasses of halide perovskites such as two-dimensional (2D) halide perovskites have begun to play a significant role in advancing the fundamental understanding of the structural, chemical, and physical properties of halide perovskites, which are technologically relevant. While the chemistry of these 2D materials is similar to that of the 3D halide perovskites, their layered structure with a hybrid organic-inorganic interface induces new emergent properties that can significantly or sometimes subtly be important. Synergistic properties can be realized in systems that combine different materials exhibiting different dimensionalities by exploiting their intrinsic compatibility. In many cases, the weaknesses of each material can be alleviated in heteroarchitectures. For example, 3D-2D halide perovskites can demonstrate novel behavior that neither material would be capable of separately. This review describes how the structural differences between 3D halide perovskites and 2D halide perovskites give rise to their disparate materials properties, discusses strategies for realizing mixed-dimensional systems of various architectures through solution-processing techniques, and presents a comprehensive outlook for the use of 3D-2D systems in solar cells. Finally, we investigate applications of 3D-2D systems beyond photovoltaics and offer our perspective on mixed-dimensional perovskite systems as semiconductor materials with unrivaled tunability, efficiency, and technologically relevant durability.

Stabilization of photoactive phases for perovskite photovoltaics

Interest in photovoltaics (PVs) based on Earth-abundant halide perovskites has increased markedly in recent years owing to the remarkable properties of these materials and their suitability for energy-efficient and scalable solution processing. Formamidinium lead triiodide (FAPbI₃)-rich perovskite absorbers have emerged as the frontrunners for commercialization, but commercial success is reliant on the stability meeting the highest industrial standards and the photoactive FAPbI₃ phase suffers from instabilities that lead to degradation - an effect that is accelerated under working conditions. Here, we critically assess the current understanding of these phase instabilities and summarize the approaches for stabilizing the desired phases, covering aspects from fundamental research to device engineering. We subsequently analyse the remaining challenges for state-of-the-art perovskite PVs and demonstrate the opportunities to enhance phase stability with ongoing materials discovery and in operando analysis. Finally, we propose future directions towards upscaling perovskite modules, multijunction PVs and other potential applications.

Crystallization and Orientation Modulation Enable Highly Efficient Doctor-Bladed Perovskite Solar Cells

With the rapid rise in perovskite solar cells (PSCs) performance, it is imperative to develop scalable fabrication techniques to accelerate potential commercialization. However, the power conversion efficiencies (PCEs) of PSCs fabricated via scalable two-step sequential deposition lag far behind the state-of-the-art spin-coated ones. Herein, the additive methylammonium chloride (MACl) is introduced to modulate the crystallization and orientation of a two-step sequential doctor-bladed perovskite film in ambient conditions. MACl can significantly improve perovskite film quality and increase grain size and crystallinity, thus decreasing trap density and suppressing nonradiative recombination. Meanwhile, MACl also promotes the preferred face-up orientation of the (100) plane of perovskite film, which is more conducive to the transport and collection of carriers, thereby significantly improving the fill factor. As a result, a champion PCE of 23.14% and excellent long-term stability are achieved for PSCs based on the structure of ITO/SnO2/FA1-xMAxPb(I1-yBry)3/Spiro-OMeTAD/Ag. The superior PCEs of 21.20% and 17.54% are achieved for 1.03 cm2 PSC and 10.93 cm2 mini-module, respectively. These results represent substantial progress in large-scale two-step sequential deposition of high-performance PSCs for practical applications.

Vacuum-Deposited Wide-Bandgap Perovskite for All-Perovskite Tandem Solar Cells

All-perovskite tandem solar cells beckon as lower cost alternatives to conventional single-junction cells. Solution processing has enabled rapid optimization of perovskite solar technologies, but new deposition routes will enable modularity and scalability, facilitating technology adoption. Here, we utilize 4-source vacuum deposition to deposit FA_0.7Cs_0.3Pb(I_xBr_1-x)₃ perovskite, where the bandgap is changed through fine control over the halide content. We show how using MeO-2PACz as a hole-transporting material and passivating the perovskite with ethylenediammonium diiodide reduces nonradiative losses, resulting in efficiencies of 17.8% in solar cells based on vacuum-deposited perovskites with a bandgap of 1.76 eV. By similarly passivating a narrow-bandgap FA_0.75Cs_0.25Pb_0.5Sn_0.5I₃ perovskite and combining it with a subcell of evaporated FA_0.7Cs_0.3Pb(I_0.64Br_0.36)₃, we report a 2-terminal all-perovskite tandem solar cell with champion open circuit voltage and efficiency of 2.06 V and 24.1%, respectively. This dry deposition method enables high reproducibility, opening avenues for modular, scalable multijunction devices even in complex architectures.

Numerical Simulation on Preparing Uniform and Stable Perovskite Wet Film in Slot-Die Coating Process

Slot-die coating is regarded as a reliable and potential technology for preparing large-area perovskite solar cells with high efficiency and low cost. Therein, the formation of continuous and uniform wet film is of significance to obtain a high-quality solid perovskite film. In this work, the rheological properties of the perovskite precursor fluid are analyzed. Then, the ANSYS Fluent is introduced to establish an integrated model of internal and external flow fields during the coating process. The model is applicable to all perovskite precursor solutions with near-Newtonian fluids. Based on the theoretical simulation of finite element analysis, the preparation of 0.8 M-FA_xCs_1-xPbI₃, one of the typical large-area perovskite precursor solutions, is explored. Accordingly, this work indicates that the coupling process parameters like the fluid supply velocity (V_in) and coating velocity (V) determine the uniformity that the solution flows out of the slit and is coated onto the substrates, and the coating windows for a uniform and stable perovskite wet film is obtained. For the upper boundary range of the coating windows, the maximum value of V and V_in follows V = 0.003 + 1.46V_in (V_in ≤ 0.1 m/s), while for its lower boundary range, the minimum value of V and V_in is V = 0.002 + 0.67V_in (V_in ≤ 0.1 m/s). When V_in is higher than 0.1 m/s, the film will break due to the excessive V. Finally, the real experiment verifies the accuracy of the numerical simulation. Hopefully, this work is of reference value for the development of the slot-die coating forming process on the perovskite precursor solution approximating Newtonian fluid.

Insights into the photovoltaic properties of indium sulfide as an electron transport material in perovskite solar cells

According to recent reports, planar structure-based organometallic perovskite solar cells (OPSCs) have achieved remarkable power conversion efficiency (PCE), making them very competitive with the more traditional silicon photovoltaics. A complete understanding of OPSCs and their individual parts is still necessary for further enhancement in PCE. In this work, indium sulfide (In₂S₃)-based planar heterojunction OPSCs were proposed and simulated with the SCAPS (a Solar Cell Capacitance Simulator)-1D programme. Initially, OPSC performance was calibrated with the experimentally fabricated architecture (FTO/In₂S₃/MAPbI₃/Spiro-OMeTAD/Au) to evaluate the optimum parameters of each layer. The numerical calculations showed a significant dependence of PCE on the thickness and defect density of the MAPbI₃ absorber material. The results showed that as the perovskite layer thickness increased, the PCE improved gradually but subsequently reached a maximum at thicknesses greater than 500 nm. Moreover, parameters involving the series resistance as well as the shunt resistance were recognized to affect the performance of the OPSC. Most importantly, a champion PCE of over 20% was yielded under the optimistic simulation conditions. Overall, the OPSC performed better between 20 and 30 °C, and its efficiency rapidly decreases above that temperature.

Monolithically-grained perovskite solar cell with Mortise-Tenon structure for charge extraction balance

Although the power conversion efficiency values of perovskite solar cells continue to be refreshed, it is still far from the theoretical Shockley-Queisser limit. Two major issues need to be addressed, including disorder crystallization of perovskite and unbalanced interface charge extraction, which limit further improvements in device efficiency. Herein, we develop a thermally polymerized additive as the polymer template in the perovskite film, which can form monolithic perovskite grain and a unique "Mortise-Tenon" structure after spin-coating hole-transport layer. Importantly, the suppressed non-radiative recombination and balanced interface charge extraction benefit from high-quality perovskite crystals and Mortise-Tenon structure, resulting in enhanced open-circuit voltage and fill-factor of the device. The PSCs achieve certified efficiency of 24.55% and maintain >95% initial efficiency over 1100 h in accordance with the ISOS-L-2 protocol, as well as excellent endurance according to the ISOS-D-3 accelerated aging test.

Anti-corrosion strategy to improve the stability of perovskite solar cells

In recent years, perovskite solar cells (PSCs) have been considered as one of the most promising photovoltaic technologies due to their solution processing, cost effectiveness, and excellent performance. The highest certified power conversion efficiency (PCE) achieved to date is 25.8%, which is approaching the best PCE of 26.81% achieved for silicon-based cells. However, perovskite materials are susceptible to various aging stressors, such as humidity, oxygen, temperature, and electrical bias, which hinder the industrialization of perovskite photovoltaic technologies. In this review, we discuss the lifetime of PSCs from the perspective of corrosion science. On one hand, benefiting from a series of anti-corrosion strategies (passivation, surface coating, machining etc.) used in corrosion science, the stability of perovskite devices is remarkably enhanced; on the other hand, given that perovskites are soft crystal lattices, which are different from traditional metals, the revealed degradation processes and specific methods to improve device operation stability can be applied to the field of corrosion, which can enrich and expand corrosion science.

Optoelectronic Devices of Large-Scale Transferred All-Inorganic Lead Halide Perovskite Thin Films

We report the large-scale transfer process for monocrystalline CsPbBr₃ thin films prepared by chemical vapor deposition (CVD) with excellent optical properties and stability. The transfer process is robust, simple, and effective, in which CsPbBr₃ thin films could be transferred to several substrates and effectively avoid chemical or physical fabrication processes to damage the perovskite surface. Moreover, the transfer process endows CsPbBr₃ and substrates with atomically clean and electronically flat interfaces. We utilize this transfer process to realize several optoelectronic devices, including a photonic laser with a threshold of 61 μJ/cm², a photodetector with a responsivity of 2.4 A/W, and a transistor with a hole mobility of 11.47 cm² V^-1 s^-1. High device performances mainly originate from low defects of high-quality single-crystal perovskite and seamless contact between CsPbBr₃ and target substrates. The large-scale nondestructive transfer process provides promising opportunities for optoelectronic applications based on monocrystalline perovskites.

In Situ and Operando Characterizations of Metal Halide Perovskite and Solar Cells: Insights from Lab-Sized Devices to Upscaling Processes

The performance and stability of metal halide perovskite solar cells strongly depend on precursor materials and deposition methods adopted during the perovskite layer preparation. There are often a number of different formation pathways available when preparing perovskite films. Since the precise pathway and intermediary mechanisms affect the resulting properties of the cells, in situ studies have been conducted to unravel the mechanisms involved in the formation and evolution of perovskite phases. These studies contributed to the development of procedures to improve the structural, morphological, and optoelectronic properties of the films and to move beyond spin-coating, with the use of scalable techniques. To explore the performance and degradation of devices, operando studies have been conducted on solar cells subjected to normal operating conditions, or stressed with humidity, high temperatures, and light radiation. This review presents an update of studies conducted in situ using a wide range of structural, imaging, and spectroscopic techniques, involving the formation/degradation of halide perovskites. Operando studies are also addressed, emphasizing the latest degradation results for perovskite solar cells. These works demonstrate the importance of in situ and operando studies to achieve the level of stability required for scale-up and consequent commercial deployment of these cells.

High Performance Inverted RbCsFAPbI3 Perovskite Solar Cells Based on Interface Engineering and Defects Passivation

Lead halide-based perovskites solar cells (PSCs) are intriguing candidates for photovoltaic technology due to their high efficiency, low cost, and simple fabrication processes. Currently, PSCs with efficiencies of >25% are mainly based on methylammonium (MA)-free and bromide (Br) free, formamide lead iodide (FAPbI3)-based perovskites, because MA is thermally instable due to its volatile nature and Br incorporation will induce blue shift in the absorption spectrum. Therefore, MA-free, Br-free formamidine-based perovskites are drawing huge research attention in recent years. The hole transporting layer (HTL) is crucial in fabricating highly efficient and stable inverted p-i-n structured PSCs by enhancing charge extraction, lowering interfacial recombination, and altering band alignment, etc. Here, this work employs a NiO_x /PTAA bi-layer HTL combined with GuHCl (guanidinium hydrochloride) additive engineering and PEAI (phenylethylammonium iodide) passivation strategy to optimize the charge carrier dynamics and tune defects chemistry in the MA-free, Br-free RbCsFAPbI3-based perovskite absorber, which boosts the device efficiency up to 22.78%. Additionally, the device retains 95% of its initial performance under continuous 1 sun equivalent LED light illumination at 45 °C for up to 500 h.

Probing proton diffusion as a guide to environmental stability in powder-engineered FAPbI3 and CsFAPbI3 perovskites

Formamidinium lead iodide-based solar cells show promising device reliability. The grain imperfection can be further suppressed by developing powder methodology. The water uptake capability is critical for the stability of α-formamidinium lead triiodide (FAPbI₃) thin films, and elucidating the migration of hydrogen species is challenging using routine techniques such as imaging or mass spectroscopy. Here, we decipher the proton diffusion to quantify indirect monitoring of H migration by following the N-D vibration using transmission infrared spectroscopy. The technique allows a direct assessment of the perovskite degradation associated with moisture. The inclusion of Cs in FAPbI₃, reveals significant differences in proton diffusion rates, attesting to its impact. CsFAPbI₃'s ability to block the active layer access by water molecules is five times higher than α-FAPbI_3, which is significantly higher than methylammonium lead triiodide (MAPbI₃). Our protocol directly probes the local environment of the material to identify its intrinsic degradation mechanisms and stability, a key requirement for optoelectronic applications.

Efficient Perovskite/Silicon Tandem Solar Cells on Industrially Compatible Textured Silicon

Monolithic perovskite/silicon tandem solar cells promise power-conversion efficiencies (PCEs) exceeding the Shockley-Queisser limit of single-junction solar cells. The conformal deposition of perovskites on industrially feasible textured silicon solar cells allows for both lowered manufacturing costs and a higher matched photocurrent density, compared to state-of-the-art tandems using front-side flat or mildly textured silicon. However, the inferior crystal quality of perovskite films grown on fully-textured silicon compromises the photovoltaic performance. Here, an anion-engineered additive strategy is developed to control the crystallization process of wide-bandgap perovskite films, which enables improved film crystallinity, reduced trap density, and conformal deposition on industrially textured silicon. This strategy allows the fabrication of 28.6%-efficient perovskite/silicon heterojunction tandem solar cells (certified 27.9%, 1 cm² ). This approach is compatible with the scalable fabrication of tandems on industrially textured silicon, demonstrating an efficiency of 25.1% for an aperture area of 16 cm² . The anion-engineered additive significantly improves the operating stability of wide-bandgap perovskite solar cells, and the encapsulated tandem solar cells retain over 80% of their initial performance following 2000 h of operation under full 1-sun illumination in ambient conditions.