Regulation of SnO2 Electron Transport Layers for Perovskite Solar Cells

Being an important part of planar heterojunction perovskite solar cells (PSCs), electron transport layer (ETL) plays important roles in enhancing the photovoltaic performance and stability of PSCs. Despite the two most commonly used ETL materials, titanium dioxide (TiO2) and tin oxide (SnO2) all being nanoparticles and fabricated through solution method, TiO2 suffers from low electron mobility, large device hysteresis, weak chemical stability and high-temperature processing. By comparison, SnO2 owns the advantages of excellent optoelectronic properties, greater stability because of its chemical inertness and low-temperature processability. We focus on the stability and interfacial charge extraction in PSCs based on SnO2 ETL. First, physical properties and advantages of SnO2 are reviewed. Then, starting from the preparation and film formation methods of SnO2 (e. g. chemical bath deposition, solution spin-coating, etc.), we further discuss the bulk and surface defects of SnO2. Finally, targeting the defect profiles of SnO2 ETL, we emphasize regulatory approaches to enhance the device stability and carrier extraction in PSCs based on interfacial passivation, bulk doping and double-ETL structures. This review article contributes to the further advancements of device performance and stability of PSCs, and provides insights for the practical application of this emerging photovoltaic technology.