Chemical Bath Deposition of Co-Doped TiO₂ Electron Transport Layer for Hysteresis-Suppressed High-Efficiency Planar Perovskite Solar Cells

Planar hybrid perovskite solar cells (PSCs) attract great attention due to their obvious advantages of low-temperature processing with a high power conversion efficiency (PCE) up to 23.32%. Here, Co-doped TiO₂ (Co-TiO₂) deposited by a straightforward low-temperature chemical bath deposition (CBD) method is explored. Using Co-TiO₂ as an electron transport layer (ETL) for the planar PSCs, the effects of doping on TiO₂ morphology, electronic properties, and solar cell performance are investigated. The PCE increases to 19.10% when the Co doping concentration is optimized at 5 mol%, an increase of 17.40% compared with that using the pristine TiO₂. Meanwhile, the notorious J–V hysteresis is suppressed to a greater extent. Considering that the low-temperature CBD is comparable with continuous roll-to-roll processing, it makes the process and the Co-TiO₂ ETL potential candidates for low-cost commercialization.