A new model of charge generation, including an indirect process for single layer organic photoconductor (OPC), was proposed and verified through experiments using OPC samples with various formulations. In the proposed process, the charge generation occurs at the surface of the photosensitive layer and is assisted by the energy propagation from the bulk layer. We propose mathematical model to describe this behavior and provide experimental evidence showing charge generation only at the surface. The proposed model was applicable to various single layer OPC formulations employing a common parameter in that model. The analytical result of the experimental data showed the prominent dependence of energy diffusion length on CGM concentration. This dependence can be explained by proposing that the disturbance of phonon migration is due to CGM particles.