Interface Defects Passivation and Conductivity Improvement in Planar Perovskite Solar Cells Using Na₂S-Doped Compact TiO₂ Electron Transport Layers

Abstract

Numerous trap states and low conductivity of compact TiO₂ layers are major obstacles for achieving high power conversion efficiency and high-stability perovskite solar cells. Here we report an effective Na₂S-doped TiO₂ layer, which can improve the conductivity of TiO₂ layers, the contact of the TiO₂/perovskite interface, and the crystallinity of perovskite layers. Comprehensive investigations demonstrate that Na cations increase the conductivity of TiO₂ layers while S anions change the wettability of TiO₂ layers, thus improving the crystallinity of perovskite layers and passivate defects at the TiO₂/PVK interface. The synergetic effects of dopants lead to a champion efficiency as high as 21.25% in unencapsulated perovskite solar cells (PSCs), with much-improved stability. Our work provides new insights on anion dopants in TiO₂ layers, which is usually neglected in previous reports, and also proposes a simple approach to produce low-cost and high-performance electron transport layers for high-performance PSCs.