Fabrication of a Highly Functional TiO₂/AZO Bilayer Electron Transport Layer for Planar Perovskite Solar Cells

A highly functional electron transport layer (ETL) is essential for fabricating stable and efficient perovskite solar cells (PvSCs). Among the various n-type materials, mesoporous titanium dioxide ( m -TiO 2 ) is the most widely used ETL in combination with a compact layer. Despite contributing to good efficiency devices, low electron mobility, and a high annealing temperature (>450 °C) to form a crystalline film in the anatase phase, the use of m -TiO 2 is a bottleneck for perovskite technology. Aluminum-doped zinc oxide (AZO) is a potential replacement for m -TiO 2 as an ETL due to its relatively high electron mobility, high transparency, and low-temperature processing. Here, we demonstrate a low-temperature solution-processed TiO 2 /AZO bilayer thin film as ETL in a planar PvSCs configuration, which exhibits a power conversion efficiency of 13.94% with a J SC of 19.49 mA/cm 2, a V OC of 1.05V, and a FF of 68% with a pixel area of 0.25 cm 2 . The unencapsulated TiO 2 /AZO-ETL-based PvSCs retained 70% of their initial efficiency after 1000 h in an ambient atmosphere. Our studies demonstrated that the solution-processed TiO 2 /AZO bilayer ETLs provide a promising approach for developing low-temperature, high-performance, and stable planar PvSCs.