Effects of aging on the mobility and lifetime of carriers in organic bulk heterojunction solar cells

Mobility and lifetime of the carriers are two very crucial parameters, which can account for the aging of a photovoltaic device, because changes in morphology, electrode/polymer interfaces, etc., will finally result in decrease of mobility and lifetime of carriers. In the present work, we have tried to explain our experimental data with the help of theoretical analysis based on our earlier model in which we have incorporated the activity at electrode interfaces in terms of density of surface states, thickness of interface layer, and tunneling probability. Calculations show that decrease in mobility for a cell under illumination is much faster than in a dark cell. Photoinduced oxidation plays a dominant role in fast degradation of the mobility. The lifetime is also seen to decrease because of modification of parameters such as interface thickness, density of interface states, and roughness. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3670411]