High-performance p-type transparent conducting CuI-Cu₂O thin films with enhanced hole mobility, surface, and stability

Low-temperature processable p-type transparent conductors are essential for flexible transparent electronics. Current research focuses primarily on wide-band gap copper-based oxides for p-type transparent conductors. However, these oxides generally exhibit inferior performance compared to their n-type counterparts, and their high preparation temperature is unfavorable for flexible electronic applications. CuI serves as a p-type transparent conductor with the ability to be prepared at low temperatures while possessing properties comparable to n-type transparent conductors. The conventional method for CuI film fabrication involves iodination of Cu films. Nevertheless, films produced through this approach exhibit a frosted-glass-like appearance and challenging-to-regulate electrical properties, rendering them unsuitable for electronic devices. In this study, we successfully developed composite films of CuI-Cu₂O, demonstrating improved surface morphology and electronic properties at room temperature. The inclusion of Cu₂O suppresses the migration of CuI grain boundaries during the iodination process, leading to a reduction in CuI grain size and the formation of a polycrystalline structure with a smoother surface. The increased concentration of grain boundaries within the films, along with charge redistribution between Cu₂O and CuI, results in a decrease in hole concentration. As the Cu₂O content increases, the relative concentration of I vacancies in the films decreases, leading to an enhancement in hole mobility. The film conductivity initially rises and subsequently decreases with higher Cu₂O content. For CuI-Cu₂O films with optimized Cu₂O composition, visible region transparency ranges from 70% to 80%, hole concentration measures 6.16 × 10¹⁸ cm⁻³, hole mobility reaches 25.40 cm² V⁻¹ s⁻¹, and conductivity amounts to 18.57 S cm⁻¹. Furthermore, after a period of six months, the electrical properties of CuI-Cu₂O films exhibit greater stability compared to pure CuI films. These findings are expected to expedite the widespread application of CuI films within transparent electronics.