Transparent <i>p</i>-type copper iodide for next-generation electronics: fundamental physics and recent research trends

Development of transparent and flexible p -type semiconductors has been a significant challenge for scientific curiosity and industrial interest. Unlike n -type metal oxide semiconductors, such as zinc oxide (ZnO), In2O3, and SnO2, transparent p -type oxide semiconductors have suffered from low optical transparency and poor electrical performance. To overcome the intrinsic limitation of p -type oxide semiconductors, copper iodide (CuI) is gaining attention as a multifunctional p -type semiconductor with excellent optical transparency, decent mechanical flexibility, high hole mobility, high electrical conductivity, and even promising thermoelectric performance. Here, we present the recent progress of CuI-based transparent p -type electronics from materials to applications. In this review, we summarize the physical and chemical properties of CuI by reviewing computational studies, focusing on the band structure, intrinsic defects, and promising dopants. Additionally, various applications of CuI, including its use as active layers, hole transport layers (HTLs), transparent electrodes, and energy harvesters, are examined, highlighting important studies and their findings. Strategies to enhance device performance, such as controlling carrier concentrations and refining fabrication methods, are discussed, offering insights for developing next-generation electronic devices. Finally, we discuss current challenges and perspective opportunities of CuI-based transparent p -type electronics.