Highly Conductive p-Type Transparent Conducting Electrode with Sulfur-Doped Copper Iodide

Although n-type transparent conductors have been commercialized with high optical transmittance and electrical conductivity, the realization of their p-type counterparts has been a challenging problem. Here, we report the synthesis of a highly conductive transparent p-type sulfur-doped CuI (CuI:S) thin film using a liquid-iodination method with a thiol additive. The CuI:S film shows a remarkably high electrical conductivity of 511 S cm–1 with an optical transmittance of greater than 80%. Furthermore, additional hole doping of CuI:S with H2O2 treatment improves the electrical conductivity to 596 S cm–1. Consequently, CuI:S exhibits a record-high figure of merit (FOM) value of 63,000 M Ω–1 (73,000 M Ω–1 with H2O2 treatment), which is ∼370% (∼430% with H2O2 treatment) higher than the previously reported record-high FOM value. The highly conducting CuI:S electrode is successfully applied as transparent conducting electrodes of the organic light-emitting diode and transparent p-type thin-film transistor. The liquid-iodination chemical method with unconventional control of the reaction parameters can be generalized to produce high-quality metal halide thin films, allowing them to be applicable for transparent electronics and optoelectronics.