A photocurrent decay model is presented that addresses the charge trapping and doping mechanisms for composite poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) films having ZnO nanoparticles of different contents. It is shown that ZnO doping introduced changes in the chemical structure of PEDOT:PSS. Dark current proportional to ZnO doping was observed. For n-type Si/ZnO-doped PEDOT:PSS devices, the high photocurrent density originates from efficient hole transport combined with long-lifetime electron trapping.