Ultrasonic spray deposition for production of organic solar cells
Recent improvements of organic photovoltaic power conversion efficiencies have motivated development of scalable processing techniques. We compare chlorobenzene and p-xylene, as solvents with similar bulk properties, in a case study of ultrasonic spray depositions of bulk heterojunction layers in photovoltaic devices. Structure and morphology of spray-deposited films are investigated via small-angle X-ray diffraction and optical microscopy. Unique phases are observed in bulk heterostructure films sprayed from p-xylene. Films sprayed from chlorobenzene resulted in higher device efficiencies than p-xylene due to large differences in film morphologies. Carrier loss mechanisms are also investigated. Post-production annealing increases power conversion efficiency to 3.2% when chlorobenzene is used.