Self-assembled complexing agent assisted chemical bath deposition of SnOX enabled highly efficient perovskite solar cells

Chemical bath deposition (CBD) is generally used to fabricate SnOX electron transport layer (ETL) for perovskite solar cells, whereas a lack of understanding of the reaction mechanism hampers further improvement of device performance. Here, we elucidate the reaction mechanism by monitoring the SnOX growth process via a series of advanced X-ray photoelectron spectroscopy studies. For the first time, we successfully modulated the nucleation and crystal growth of SnOX during the CBD process by introducing complexing agent via inherently forming a self-assembled monolayer on the outmost surface of SnOX. The complexing agents can assist the heterogeneous nucleation and crystal growth of SnOX. By a comparison study of different complexing agents, we found that the 2,3-dimercapto-1-propanesulfonate sodium not only assist in achieving a high-quality SnOX ETL, but also serve as a bridge to connect with perovskite via coordination interactions. Leveraging these insights, we achieved a champion efficiency of 24.2 % for perovskite solar cells with ∼ 2300 h stability at ambient condition.