Influence of anode roughness and buffer layer nature on organic solar cells performance

Fluorine doped transparent conductive tin oxide thin films (FTO) of different surface roughness have been deposited by chemical vapor deposition (FTO_SOL), classical chemical spray pyrolysis (FTO_CSP), and spray pyrolysis onto heated substrates using infra red irradiation (FTO_IRSP); the three deposition methods inducing different surface roughness. It was found that the different FTOs presented similar electrical properties while their structural, morphological and optical properties were related to surface properties. These FTO films have been used as anode in multilayer organic solar cells, based on coupled donor/acceptor-copper phthalocyanine/fullerene. To improve solar cell performance, buffer layers of different natures have been tried at the anode/organic material interface. Deposition of a thin molybdenum oxide film onto FTO smooth films afforded reproducible devices with performance similar to those obtained with indium tin oxide anodes. However, cell efficiency decreased as FTO surface roughness increased. The degree of degradation depended on the nature of the buffer layer. We show that it is necessary to use buffer layer material that allows consistency and completeness of the electrode coverage.