SnO₂–Carbon Nanotubes Hybrid Electron Transport Layer for Efficient and Hysteresis-Free Planar Perovskite Solar Cells

Tin oxide (SnO₂) has recently received increasing attention as an electron transport layer (ETL) in planar perovskite solar cells (PSCs) and is considered a possible alternative to titanium oxide (TiO₂). However, planar devices based on pure solution-processed SnO₂ ETL still have hysteresis, which greatly limits the application of SnO₂ in high-efficiency solar cells. Herein, to address this issue, a hybrid ETL of SnO₂ and carbon nanotubes (CNTs) is fabricated by a simple thermal decomposing of a mixed solution of SnCl₄·5H₂O and pretreated CNTs (termed SnO₂–CNT). The addition of CNTs can significantly improve the conductivity of SnO₂ films and reduce the trap-state density of SnO₂ films, which benefit carrier transfer from the perovskite layer to the cathode. As a result, a high efficiency of 20.33% is achieved in the hysteresis-free PSCs based on SnO₂–CNT ETL, which shows 13.58% enhancement compared with the conventional device (power conversion efficiency = 17.90%).