Co-Doping Approach for Enhanced Electron Extraction to TiO₂ for Stable Inorganic Perovskite Solar Cells

Inorganic perovskite CsPbI₃ solar cells hold great potential for improving the operational stability of perovskite photovoltaics. However, electron extraction is limited by the low conductivity of TiO₂, representing a bottleneck for achieving stable performance. In this study, a co-doping strategy for TiO₂ using Nb(V) and Sn(IV), which reduces the material's work function by 80 meV compared to Nb(V) mono-doped TiO₂, is introduced. To gain fundamental understanding of the processes at the interfaces between the perovskite and charge-selective layer, transient surface photovoltage measurements are applied, revealing the beneficial effect of the energetic and structural modification on electron extraction across the CsPbI₃/TiO₂ interface. Using 2D drift-diffusion simulations, it is found that co-doping reduces the interface hole recombination velocity by two orders of magnitude, increasing the concentration of extracted electrons by 20%. When integrated into n–i–p solar cells, co-doped TiO₂ enhances the projected T_S80 lifetimes under continuous AM1.5G illumination by a factor of 25 compared to mono-doped TiO₂. This study provides fundamental insights into interfacial charge extraction and its correlation with operational stability of perovskite solar cells, offering potential applications for other charge-selective contacts.