Controllable synthesis and n-doping of HMoOx nanoparticle inks through simple photoreduction for solution-processed organic photovoltaics

Solution-processable hole transporting layer (HTL) is one basis for the full-solution-processable fabrication of the organic solar cells (OSCs). Molybdenum oxide (MoO x ) is a widely used HTL and has the possibility of solution processing. Controlling the valence state of molybdenum (Mo) in MoO x HTL is critical for OSCs performance. In this work, we developed a novel methode based on photochemical reduction to synthesize HMoO x nanoparticle ink for OSCs. HMoO 3 nanoparticle was firstly obtained through oxidaiton of metal molybdenum. Afterward, the HMoO 3 precursor nanoparticles were continuously illuminated to induce the reduction of Mo(VI) to Mo(V) to form HMoO x . Such a process could proceed under the illumination of different light sources, even sunlight. In addition, photoelectron spectroscopy (XPS) and absorption spectra demonstrated such a photoreduction process was well controllable by illumination intensity and illumination time. With this HMoO x HTL for the inverted OSCs, a high efficiency of 13.17% and 16.64% for the PM7:IT-4F and PM6:Y6 OSCs was obtained, which is comparable with the evaporated MoO 3 HTL-based OSCs. Furthermore, based on the Ag nanowires (AgNWs) electrode, the performances of all-solution-processed PM6:Y6 semitransparent device also reach 10.52%. This work provides a simple and feasible route to fabricate hole transporting layer for solution-processable OSCs.