Efficient and Stable Inverted Planar Perovskite Solar Cells Employing CuI as Hole-Transporting Layer Prepared by Solid–Gas Transformation

The inorganic p-type semiconductor CuI possesses several unique characteristics such as high transparency, low-production cost, high hole mobility, and good chemical stability and is a promising hole-transporting material candidate that can be explored in solar-cell devices. Herein, we adopt a simple solid–gas reaction method to fabricate a uniform CuI film by exposing a thermally evaporated copper film to iodine vapor and apply it as a hole-transporting layer (HTL) in inverted planar perovskite solar cells (PSCs). The optimized devices display a promising power conversion (PCE) efficiency of 14.7 %, with an open-circuit voltage of 1.04 V, a short-circuit current density of 20.9 mW cm −2 , and a fill factor of 0.68. This is one of the highest PCE values reported so far for CuI-based HTL in PSCs. Moreover, the devices studied also exhibit good long-term stability at ambient atmosphere, arising from the hydrophobicity of CuI HTL. The results highlight that CuI fabricated using the simple and low-temperature processing method presented here holds great promise as low-cost alternative HTL material for the development of efficient and stable inverted planar PSCs in the future.