Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron-selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO2 )/compact TiO2 stack has been among the most used ESLs in state-of-the-art PSCs. However, this material requires high-temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO2 ) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low-temperature processability enables compatibility with temperature-sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO2 as a perovskite-relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno-economic analysis of SnO2 materials for large-scale deployment, together with a processing-toxicology assessment, is presented. Finally, a perspective on how SnO2 materials can be instrumental in successful large-scale module and perovskite-based tandem solar cell manufacturing is provided.

Tin Oxide Electron‐Selective Layers for Efficient, Stable, and Scalable Perovskite Solar Cells

3D perovskite solar cells (PSCs) have shown great promise for use in next-generation photovoltaic devices. However, some challenges need to be addressed before their commercial production, such as enormous defects formed on the surface, which result in severe SRH recombination, and inadequate material interplay between the composition, leading to thermal-, moisture-, and light-induced degradation. 2D perovskites, in which the organic layer functions as a protective barrier to block the erosion of moisture or ions, have recently emerged and attracted increasing attention because they exhibit significant robustness. Inspired by this, surface passivation by employing 2D perovskites deposited on the top of 3D counterparts has triggered a new wave of research to simultaneously achieve higher efficiency and stability. Herein, we exploited a vast amount of literature to comprehensively summarize the recent progress on 2D/3D heterostructure PSCs using surface passivation. The review begins with an introduction of the crystal structure, followed by the advantages of the combination of 2D and 3D perovskites. Then, the surface passivation strategies, optoelectronic properties, enhanced stability, and photovoltaic performance of 2D/3D PSCs are systematically discussed. Finally, the perspectives of passivation techniques using 2D perovskites to offer insight into further improved photovoltaic performance in the future are proposed. 

Surface Passivation Using 2D Perovskites toward Efficient and Stable Perovskite Solar Cells

A facile and low-temperature process to prepare planar perovskite solar cells (PSCs) has led to considerable progress in flexible solar cells toward high throughput production based on a roll-to-roll process. However, the performance of planar PSCs is still lower than that of mesoscopic PSCs using a high temperature process. Here, we report a new concept of a low temperature processed porous planar electron transport layer (ETL) inspired by a mesoporous structure for improving the performance of flexible devices. The structurally and energetically designed porous planar ETL induced the formation of a high quality perovskite and a preferred band alignment, resulting in improved charge collection efficiency in a fabricated device. Through the porous planar ETL, we achieved a power conversion efficiency (PCE) of 20.7% with a certified efficiency of 19.9% on a flexible substrate, which is the highest PCE reported to date. In addition, for the first time, we succeed in fabricating a large area flexible module with the porous planar ETL, demonstrating a PCE of 15.5%, 12.9% and 11.8% on an aperture area of 100 cm2, 225 cm2 and 400 cm2, respectively. We believe that this strategy will pave a new way for realizing highly efficient flexible PSCs.

Record-efficiency flexible perovskite solar cell and module enabled by a porous-planar structure as an electron transport layer

The defect passivation of perovskite films is an efficacious way to further boost the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). In this work, ionic...

Interface Engineering of Imidazolium Ionic Liquids toward Efficient and Stable CsPbBr3 Perovskite Solar Cells.

Hole transport layers (HTLs) play a crucial role in the efficiency and stability of perovskite solar cells (PSCs). The most efficient PSCs based on spiro-OMeTAD (Spiro) generally have stability pro...

NiOx/Spiro Hole Transport Bilayers for Stable Perovskite Solar Cells with Efficiency Exceeding 21%

Efficient and Stable 2D@3D/2D Perovskite Solar Cells Based on Dual Optimization of Grain Boundary and Interface

Colloidal synthesis of Y-doped SnO2 nanocrystals for efficient and slight hysteresis planar perovskite solar cells

Excellent quinoline additive in perovskite toward to efficient and stable perovskite solar cells

Organic–inorganic halide perovskite solar cells with excellent photovoltaic properties still have some potential for further enhancement in device performance. Charge loss and carrier recombination at interfaces in perovskite solar cells are crucial factors that inhibit the power conversion efficiency. Here, we report a simple approach to overcome the drawbacks via modifying the interfaces between charge transport layers and perovskite layers in the perovskite solar cells with NiO nanocrystals. The optimized device achieves an excellent power conversion efficiency as high as 19.47%. The interface engineering with NiO nanocrystals results in improved interface contact properties, enhanced charge transport dynamics and suppressed charge recombination in the corresponding devices, which further contribute to increased values of open-circuit voltage and short-circuit current density. Therefore, this work provides novel guidelines toward dual interfacial modification engineering to boost the performance of perovskite solar cells.

Jing Song

Papers

Efficient and Stable 2D@3D/2D Perovskite Solar Cells Based on Dual Optimization of Grain Boundary and Interface

Colloidal synthesis of Y-doped SnO2 nanocrystals for efficient and slight hysteresis planar perovskite solar cells

Excellent quinoline additive in perovskite toward to efficient and stable perovskite solar cells

Dual interfacial modification engineering with p-type NiO nanocrystals for preparing efficient planar perovskite solar cells

Influence of Polymer Additives on the Efficiency and Stability of Ambient‐Air Solution‐Processed Planar Perovskite Solar Cells