Fabrication of Thermally Evaporated CuI_x Thin Films and Their Characteristics for Solar Cell Applications

Carrier-selective contacts (CSCs) for high-efficiency heterojunction solar cells have been widely studied due to their advantages of processing at relatively low temperatures and simple fabrication processes. Transition metal oxide (TMO) (e.g., molybdenum oxide, vanadium oxide, and tungsten oxide) thin films are widely used as hole-selective contacts (HSCs, required work function for Si solar cells > 5.0 eV). However, when TMO thin films are used, difficulties are faced in uniform deposition. In this study, we fabricated a copper (I) iodide (CuI) thin film (work function > 5.0 eV) that remained relatively stable during atmospheric exposure compared with TMO thin films and employed it as an HSC layer in an n-type Si solar cell. To facilitate efficient hole collection, we conducted iodine annealing at temperatures of 100–180 °C to enhance the film’s electrical characteristics (carrier density and carrier mobility). Subsequently, we fabricated CSC Si solar cells using the annealed CuI_x layer, which achieved an efficiency of 6.42%.