Tin Oxide Bilayer as Effective Electron Transport Layers for Efficient and Stable Perovskite Solar Modules

Tin oxide (SnO 2 ) is one of the most promising electron transport layers (ETL) for the commercialization of perovskite solar cells (PSCs) due to its excellent electron mobility and high transparency, along with its low processing temperature. However, the inherent defects, nonuniform coating, and poor surface morphology of SnO 2 may be detrimental to the physicochemical properties, such as conductivity and electron mobility at the interface, lead to a decrease in the open‐circuit voltage ( V OC ) and a reduction in device stability. In this study, a method that combines atomic layer deposition and chemical bath deposition techniques to solve these issues is presented. The presence of bilayer ETLs enhances the coverage of the SnO 2 film and optimizes the morphology of the buried surface of perovskite, which not only facilitates the interfacial charge transfer but also suppresses recombination reactions. As a result, a significant increase in V OC and efficiency has been achieved compared to devices with only a single layer. Additionally, the large‐area perovskite solar module (active area: 48.0 cm 2 ) achieves a champion efficiency of 17.9%. The PSCs retain more than 93% of their initial efficiency after 700 h of continuous operation under 1‐sun illumination and 25 °C.