An Er-doped TiO2 phase junction as an electron transport layer for efficient perovskite solar cells fabricated in air

Current perovskite solar cells (PSCs) often use high-purity single-crystal metal oxides prepared by complex growth processes as electron transport layers (ETLs). In particular, TiO2, as an ETL, can deteriorate the stability of PSCs under illumination. Here, we report a passivation strategy using Er-doped TiO2 synthesized with a one-step hydrothermal method as an ETL. Notably, the oxygen-induced defects in TiO2 have decreased to an acceptable level for PSCs due to the introduction of Er3+ ions. More interestingly, we find that a phase junction can be formed in the mixed crystalline rutile/anatase phase of TiO2, and this TiO2 phase junction can achieve efficient charge separation and accelerate internal electron transfer of the ETL. Taking advantage of these facts, we obtain TiO2-based PSCs through a two-step sequential deposition method in ambient air, whose best efficiency increases by 45.8%. Moreover, the Er-doped device exhibits remarkable ultraviolet resistance ability, whose efficiency is maintained over 90% even after 500 hour ultraviolet irradiation. We believe that this demonstrated strategy provides an effective way for preparing efficient and ultraviolet resistant PSCs in air.