Photodeposited polyamorphous CuOx hole-transport layers in organic photovoltaics

Hole-selective charge transport layers are an important part of modern thin-film electronics, serving to direct electron flow and prevent leakage current. Crystalline metal-oxide hole-transport layers (HTLs) such as NiO and CuOx exhibit high performance and stability. However they are traditionally not amenable to scalable and sustainable solution-processing techniques. Conversely, amorphous metal oxides are much more readily prepared by lowtemperature solution processing methods but often lack the charge transport properties of crystalline semiconductors. Herein we report the fabrication of amorphous a-CuOx thin films from commercially available starting material using a simple UV-based thin-film deposition method. Subsequent thermal annealing of the a-CuOx induces an amorphous-to-amorphous phase transition resulting in p-type semiconducting behavior. The resulting thin films were used as HTLs in organic photovoltaic devices with power conversion efficiencies comparable to those fabricated with PEDOT:PSS.