Modification of SnO₂ electron transport Layer: Brilliant strategies to make perovskite solar cells stronger

The organic–inorganic hybrid perovskite solar cells (PSCs) have been emerging as a promising photovoltaic technology with the rapid development of power conversion efficiency (PCE). The electron transport layer (ETL) is found to play a critical role in the PCE, stability and reliability of the solar cells. SnO₂, which can be processed at low temperature and possesses the merits of good energy band level and high electron mobility, has been deemed as an excellent alternative ETL material to the classical TiO₂. In the past few years, modifications that can finely tailor the morphologies, crystallinity, energy level, electron mobility, conductivity, defects, surface chemical states, and interface condition of SnO₂-ETL have contributed dominantly to the fast development of the SnO₂-ETL based PSCs. In this review, the recent advances of modified SnO₂ as ETLs for PSCs are summarized and the corresponding mechanisms for the performance improvements are comprehensively discussed. Finally, the challenges and the opportunities for the future development of SnO₂-ETL based PSCs are proposed.