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

Abstract 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.