Advancing SnO₂ Electron Transport Layer for Efficient Perovskite Photovoltaics: A Critical Review

Currently, the latest photovoltaic technology based on perovskite solar cells (PSCs) has attracted much attention due to the low cost, exciting power conversion efficiency of over 26%, large scalability, and flexibility of PSCs. During the development course, optimization of the electron transport layer (ETL) plays an important role in boosting the photovoltaic performance of PSCs, where the use and modification of SnO₂ with high chemical stability, low-temperature processability, and suitable energy band levels substantially are shown to solve the problems of poor charge transport, perovskite crystallization, and inferior stability at the PSC interface. Herein, we dedicate ourselves to providing a comprehensive review of the advanced development of the SnO₂ ETL for realizing efficient PSCs. The fundamental properties of SnO₂ and its key problems as an ETL in PSCs are summarized first. Then, the typical preparation methods are introduced, including chemical routes and physical routes. Sequentially, the state-of-the-art strategies for optimizing the quality of the SnO₂ ETL are discussed, such as defect regulation, self-assembled monolayer modification, and double ETL construction. Finally, we shed some light on the existing challenges and future research directions for the large-scale development of SnO₂-based PSCs.