Abstract Light-harvesting material Sb2S3 has recently attracted tremendous attention due to its excellent photovoltaic properties. Extensive efforts have been exerted to improve the power conversion efficiency through process innovation, interface modification and band gap engineering. In this study, we report an all-inorganic planar heterojunction Sb2S3 solar cell using NiOx as hole extraction material, which is deposited from preformed NiOx nanoparticle solution. We demonstrate that the device performance can be significantly enhanced upon O2 plasma treatment on NiOx layer. As a result, O2 plasma-treated NiOx hole conductor leads to a 43% enhancement in power conversion efficiency when compared to untreated one, delivering an efficiency of 3.51%. The enhancement mechanisms are interpreted in terms of electronic structures and interfacial charge transport properties characterized by synchrotron-based high resolution ultraviolet photoelectron spectroscopy and electrochemical impedance spectroscopy. This work provides a choice of novel inorganic hole-transporting material for the preparation of stable and efficient all-inorganic solar cell device based on Sb2S3 as well as Sb2(S,Se)3.