Extrinsic photocarrier generation in a dual-layered organic device consisting of fluorenone-bisazo-pigment-based carrier generation layer (CGL) in combination with triphenylamine-derivative-based carrier transport layer (CTL) was investigated in order to elucidate the carrier generation pathways accurately and to improve the carrier generation efficiency. As a result, photocarrier generation was proven to occur via the following reaction pathways; (i) exciton produced by photon absorption in the bulk of the CGL diffuses to the CGL/CTL interface, (ii) the exciton makes photoinduced electron transfer to generate a geminate pair at the interface which competes with the deactivation of the exciton, and (iii) the geminate pair dissociates into free carriers that compete with geminate recombination. The overall photocarrier generation efficiency was expressed by using these reaction rates. The efficiency was then simplified to an expression that involves four elementary processes of (i) photoinduced electron transfer, (ii) deactivation of the azo excited state, (iii) dissociation of geminate pair and (iv) geminate recombination. The reactions, except for the azo excited state deactivation, were considered to occur between the neighboring two molecules and to obey the electron transfer theory. The method to improve the efficiency is discussed based on electron transfer theory.