Solution Synthesized p‑Type Copper Gallium Oxide Nanoplates as Hole Transport Layer for Organic Photovoltaic Devices

p-Type metal-oxide hole transport layer (HTL) suppresses recombination at the anode and hence improves the organic photovoltaic (OPV) device performance. While NiO_x has been shown to exhibit good HTL performance, very thin films (<10 nm) are needed due to its poor conductivity and high absorption. To overcome these limitations, we utilize CuGaO₂, a p-type transparent conducting oxide, as HTL for OPV devices. Pure delafossite phase CuGaO₂ nanoplates are synthesized via microwave-assisted hydrothermal reaction in a significantly shorter reaction time compared to via conventional heating. A thick CuGaO₂ HTL (∼280 nm) in poly­(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) devices achieves 3.2% power conversion efficiency, on par with devices made with standard HTL materials. Such a thick CuGaO₂ HTL is more compatible with large-area and high-volume printing process.