We display that the process of charge carriers' separation at molecular photocells is a complex phenomenon that is controlled by the cumulative action of Coulomb interaction for electron-hole pairs and LUMO-LUMO offset energies. By applying quantum scattering theory and the Lippmann-Schwinger equation, we provide a comprehensive framework of the device operation in which the operating molecular photocell is described by a wave function. We find that depending on the magnitude of offset energies, the electron-hole interaction can normally decrease or abnormally increase the charge separation yield. To rationalize the results, we benefit from the spectral information provided in the model. Our analysis helps to optimize molecular photocells operation.