Organic photovoltaic devices incorporating a molybdenum oxide hole-extraction layer deposited by spray-coating from an ammonium molybdate tetrahydrate precursor

Abstract Polymer bulk heterojunction solar cells have been constructed using a thin film molybdenum oxide (MoOx) hole extraction layer that was fabricated by thermally annealing an ammonium molybdate tetrahydrate precursor layer deposited in air by ultrasonic spray-coating. Onto this layer was spray cast a PCDTBT:PC71BM film that acted as the active light-harvesting and charge-transporting layer. We optimise the processing steps used to convert the spray-cast MoOx precursor and show that the temperature at which it is annealed is critical to achieving high device efficiency as it both facilitates the removal of trapped solvent as well as driving its chemical conversion to MoOx. We demonstrate that by optimising the spray-casting and annealing process, we are able to create solar cell devices having a peak power conversion efficiency of 4.4%.