  Delafossites like CuGaO2 have appeared as promising p-type semiconductor
materials for opto-electronic applications mainly due to their high optical
transparency and electrical conductivity. However, existing synthetic efforts
usually result in particles with large diameter limiting their performance
relevant to functional electronic applications. In this article, we report a
novel surfactant-assisted hydrothermal synthesis method, which allows the
development of ultrafine (~5 nm) monodispersed p-type CuGaO2 nanoparticles
(NPs). We show that DMSO can be used as a ligand and dispersing solvent for
stabilizing the CuGaO2 NPs. The resulting dispersion is used for the
fabrication of dense, compact functional CuGaO2 electronic layer with
properties relevant to advanced optoelectronic applications. As a proof of
concept, the surfactant-assisted hydrothermal synthesized CuGaO2 is
incorporated as a hole transporting layer (HTL) in the inverted p-i-n
perovskite solar cell device architecture providing improved hole carrier
selectivity and power conversion efficiency compared to conventional PEDOT:PSS
HTL based perovskite solar cells.
