Efficient and Stable Planar n‐i‐p Perovskite Solar Cells with Negligible Hysteresis through Solution‐Processed Cu 2 O Nanocubes as a Low‐Cost Hole‐Transport Material

Organic-inorganic halide perovskite solar cells (PSCs) have reached certified efficiencies of over 23 % with expensive organic hole-transporting materials. However, the use of an inorganic hole-transport layer (HTL) remains crucial as it would reduce cost combined with higher mobility and stability. In this direction, the application of Cu2 O as the top layer in PSCs is still complicated owing to the difficulty of solution processing. Herein, a solution-processing method is reported for preparing Cu2 O nanocubes as a p-type HTL in regular structure (n-i-p) PSCs. The controlled synthesis of Cu2 O nanocubes in a size range of 60-80 nm is achieved without using any surfactants, which are usually toxic and tricky to remove. The new structure of these Cu2 O nanocubes enhances the carrier mobility with preferable energy alignment to the perovskite layer and superb stability. The PSCs based on these Cu2 O nanocubes HTMs could achieve an efficiency exceeding 17 % with high stability, whereas organic P3HT-based PSCs display an efficiency of 15.59 % with a poorer running stability. This indicates that Cu2 O nanocubes are a promising HTM for efficient and stable PSCs.