To achieve superior photovoltaic performance on Sb2S3 solid state solar cells (ssSCs), the concomitant development of efficient hole transport materials (HTMs) is required. Herein, a novel solution processed HTM obtained by mixing NiOx nanoparticles (NiOx-NP) and poly(3-hexylthiophene) (P3HT) is reported. These P3HT:NiOx-NP nanocomposite HTMs were obtained with different controlled concentrations of NiOx-NP using a common solvent. Incorporation of NiOx-NP significantly impacts on the structural and hole-transport layer properties of the nanocomposite films, which in turn contributes to improve the photovoltaic performance of the corresponding devices. Thus, Sb2S3 ssSCs based on HTM with an optimum concentration of NiOx-NP in P3HT, i.e. P3HT:2% NiOx-NP, yield a 50% improvement in the power conversion efficiency relative to control devices fabricated with pristine P3HT. The improved hole separation and injection at the Sb2S3/HTM interface, determined by steady-state photoluminescence quenching and electrochemical impedance spectroscopy studies, correlate well with the higher hole mobility of the nanocomposite and the current density and fill factor enhancements. (C) 2018 Elsevier Inc. All rights reserved.