Degradation of organic solar cells studied by displacement current

Large displacement current and then apparent external quantum efficiency are observed for 'dead' (no photocurrent under steady-state illumination) organic solar cells under chopped light illumination. This displacement current is generated from charge trapping and detrapping under non-steady-state illumination, reflecting a large number of trap states in the devices. The photocurrent degradation of organic solar cells is suggested to be caused by these traps. Thus a physical degradation process of organic solar cells is proposed: the filled traps would hinder the transport of free carriers from the donor-acceptor interface to the electrodes on the one hand and quench the excitons generated in the active layer on the other hand.