Properties and Applications of Copper(I) Thiocyanate Hole‐Transport Interlayers Processed from Different Solvents

Copper(I) thiocyanate (CuSCN) is an effective interlayer material for hole injection and transport in organic electronic devices but its solution processing has conventionally utilized undesirable di‐n‐alkyl sulfide solvents such as diethyl‐ (DES) and dipropyl‐sulfide (DPS). Herein, this paper reports on the use of N,N‐dimethylformamide (DMF) and 1‐methyl‐2‐pyrrolidinone (NMP) as alternative solvents for CuSCN interlayers and performs a detailed comparison of the resulting properties relative to films processed from DES and DPS and two other recent alternatives, dimethyl sulfoxide (DMSO) and ammonium hydroxide. The surface roughness, polymorphism, and surface chemistry of the resulting CuSCN layers are reported. The interlayer surface energy and ionization potential that are key to the overlying semiconductor microstructure and interfacial energy barrier, and hence to charge transport and injection, are also discussed. Finally, systematic device tests using well‐known organic semiconductors in light‐emitting diode, solar cell and field‐effect transistor structures demonstrate the overall suitability of DMSO and DMF as solvents for CuSCN interlayer deposition to achieve better device performance. This study broadens the applicability of CuSCN as a highly efficient hole injection/transport material for organic semiconductor devices by expanding the documented range of suitable CuSCN solvents. The solvent effects on a solution‐processable hole injection/transport material, copper(I) thiocyanate (CuSCN), are investigated. Six solvent candidates are examined for their impacts on the resulting CuSCN thin‐film topography, roughness, polymorphism, composition, surface energy, and ionization potential. Results from representative organic semiconductor devices demonstrate the overall suitability of dimethyl sulfoxide and N,N‐dimethylformamide as solvents for CuSCN interlayer deposition to achieve better performance.