Room-temperature processed TiO₂ to construct composite electron transport layers for efficient planar perovskite solar cells

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) is seriously affected by the conductivity and energy alignment of the electron transport layer (ETL). However, poor film quality leads to low conductivity and interface energy level mismatch, which limits the performance of PSCs. Herein, a simple room-temperature (<35 degrees C) method is used to produce high-quality amorphous TiO2 thin films by vacuum ultraviolet (VUV) light (172 nm), to form composite ETLs with SnO2 for PSCs. The introduction of TiO2 produced perovskite films with larger grains and low trap density. The experimental results and density functional theory (DFT) analysis show that the composite ETL structure improves the electron mobility and conductivity, and the interaction with SnO2 accelerates the electron extraction due to favorable energy level alignment with the perovskite layer. Eventually, the composite ETL-based PSCs obtain a champion PCE of 24.59% (certified efficiency of 24.24%) and retain 92.4% of their initial PCE after 500 h of continuous light exposure.