Study of the Hole Transport Processes in Solution‐Processed Layers of the Wide Bandgap Semiconductor Copper(I) Thiocyanate (CuSCN)

Abstract

Wide bandgap hole‐transporting semiconductor copper(I) thiocyanate (CuSCN) has recently shown promise both as a transparent p‐type channel material for thin‐film transistors and as a hole‐transporting layer in organic light‐emitting diodes and organic photovoltaics. Herein, the hole‐transport properties of solution‐processed CuSCN layers are investigated. Metal–insulator–semiconductor capacitors are employed to determine key material parameters including: dielectric constant [5.1 (±1.0)], flat‐band voltage [−0.7 (±0.1) V], and unintentional hole doping concentration [7.2 (±1.4) × 1017 cm−3]. The density of localized hole states in the mobility gap is analyzed using electrical field‐effect measurements; the distribution can be approximated invoking an exponential function with a characteristic energy of 42.4 (±0.1) meV. Further investigation using temperature‐dependent mobility measurements in the range 78–318 K reveals the existence of three transport regimes. The first two regimes observed at high (303–228 K) and intermediate (228–123 K) temperatures are described with multiple trapping and release and variable range hopping processes, respectively. The third regime observed at low temperatures (123–78 K) exhibits weak temperature dependence and is attributed to a field‐assisted hopping process. The transitions between the mechanisms are discussed based on the temperature dependence of the transport energy.