Room-temperature solution-processed molybdenum oxide as a hole transport layer with Ag nanoparticles for highly efficient inverted organic solar cells

While metal oxide films are typically formed by high-temperature and sputtering processes, we report an approach with the features of a room-temperature, water-free and solution-based process for the formation of a molybdenum oxide (MoOx) film for inverted organic solar cells (OSCs) by proposing a vacuum treatment at room temperature and selecting an appropriate solvent. Remarkably, our results indicate that the vacuum treatment can introduce oxygen vacancies in the molybdenum oxide film and modify its work function for functioning as an efficient hole transport layer. To further improve OSC performances, a silver nanoparticle-molybdenum oxide (Ag NP-MoOx) composite film is prepared by the introduction of Ag nanoparticles into the solution. Evidence and explanations confirm that OSC performance enhancement is mainly due to the improvement of the electrical properties of the Ag NP-MoOx composite film. With the optimized composite film, inverted OSCs with a power conversion efficiency (PCE) of 7.94% are achieved. Through the demonstration of high performance inverted OSCs with different polymer materials, the water-free, room-temperature and solution-processed MoOx can contribute to the evolution of high performance OSCs such as inverted and tandem OSCs and other optoelectronic devices.