Engineering Copper Iodide (CuI) for Multifunctional p‐Type Transparent Semiconductors and Conductors

Developing transparent p‐type semiconductors and conductors has attracted significant interest in both academia and industry because metal oxides only show efficient n‐type characteristics at room temperature. Among the different candidates, copper iodide (CuI) is one of the most promising p‐type materials because of its widely adjustable conductivity from transparent electrodes to semiconducting layers in transistors. CuI can form thin films with high transparency in the visible light region using various low‐temperature deposition techniques. This progress report aims to provide a basic understanding of CuI‐based materials and recent progress in the development of various devices. The first section provides a brief introduction to CuI with respect to electronic structure, defect states, charge transport physics, and overviews the CuI film deposition methods. The material design concepts through doping/alloying approaches to adjust the optoelectrical properties are also discussed in the first section. The following section presents recent advances in state‐of‐the‐art CuI‐based devices, including transparent electrodes, thermoelectric devices, p–n diodes, p‐channel transistors, light emitting diodes, and solar cells. In conclusion, current challenges and perspective opportunities are highlighted.