Composite SnO2–K2S ETL for energy level regulation and electron mobility enhancement in perovskite solar cells

High-performance perovskite solar cells commonly utilize SnO₂ as the electron transport layer (ETL), which is vital for perovskite crystallization and defect regulation, yet energy level mismatch, oxygen vacancies in SnO₂, and defects at the buried interface impede the device's photovoltaic performance. Therefore, we found that incorporating K₂S into the SnO₂ layer effectively regulated the energy levels and occupied oxygen vacancies, enhancing the electron mobility of the composite SnO₂-K₂S ETL and improving the interface quality to promote efficient electron extraction and transport. Consequently, the device based on SnO₂-K₂S ETL showed an enhanced photovoltaic performance with power conversion efficiency of to 23.28%.