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 (MoOx) is a widely used HTL and has the possibility of solution processing. Controlling the valence state of molybdenum (Mo) in MoOx HTL is critical for OSCs performance. In this work, we developed a novel methode based on photochemical reduction to synthesize HMoOx nanoparticle ink for OSCs. HMoO3 nanoparticle was firstly obtained through oxidaiton of metal molybdenum. Afterward, the HMoO3 precursor nanoparticles were continuously illuminated to induce the reduction of Mo(VI) to Mo(V) to form HMoOx. 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 HMoOx 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 MoO3 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.