Progress and Challenges of SnO2 Electron Transport Layer for Perovskite Solar Cells: A Critical Review

Organic inorganic halide perovskites have drawn great attention in the past decade, due to their superior photovoltaic performance with an efficiency over 25%. For planar heterojunction structure perovskite solar cells (PSCs) tin oxide based electron transport layers (ETLs) have become one of the most suitable candidates to replace titanium oxide to make flexible devices because of their low-temperature processing. The deposition techniques of SnO2 can be categorized into chemical deposition, such as sol-gel, chemical bathing or atomic layer deposition, and physical deposition, such as thermal evaporation or sputtering. Depending on the deposition technique, defects, and morphology in the SnO2 layer may vary drastically, leading to poor performance of PSCs. In this review, we have provided a comprehensive picture of the recent progress and challenges of different SnO2 ETL deposition techniques and the performance of PSC devices. The additional modifications on SnO2 mentioned in this article are also effective ways to eliminate the intrinsic defects in the film. The drawbacks and benefits of SnO2 ETLs and the corresponding actions for this are also discussed. We hope this review will help with the comprehensive understanding of the relationship between the property of SnO2 and its structure of ETLs to enhance PSCs' performance.