Mild solution-processed metal-doped TiO₂ compact layers for hysteresis-less and performance-enhanced perovskite solar cells

TiO₂ is extensively used as electron-transporting material on perovskite solar cells (PSCs). However, traditional TiO₂ processing method needs high annealing temperature (>450 °C) and pure TiO₂ suffers from low electrical mobility and poor conductivity. In this study, a general one-pot solution-processed method is devised to grow uniform crystallized metal-doped TiO₂ thin film as large as 15 × 15 cm². The doping process can be controlled effectively via a series of doping precursors from niobium (V), tin (IV), tantalum (V) to tungsten (VI) chloride. As far as we know, this is so far the lowest processing temperature for metal-doped TiO₂ compact layers, as low as 70 °C. The overall performance of PSCs employing the metal-doped TiO₂ layers is significantly improved in term of hysteresis effect, short circuit current, open-circuit voltage, fill factor, power conversion efficiency, and device stability. With the insertion of metal ions into TiO₂ lattice, the corresponding CH₃NH₃PbI₃ PSC leads to a ∼25% improved PCE of over 16% under irradiance of 100 mW cm⁻² AM1.5G sunlight, compared with control device. The results indicate that this mild solution-processed metal-doped TiO₂ is an effective industry-scale way for fabricating hysteresis-less and high-performance PSCs.