Microscopic nonequilibrium theory of quantum well solar cells

We present a microscopic theory of bipolar quantum well structures in the photovoltaic regime, based on the nonequilibrium Green’s function formalism for a multiband tight-binding Hamiltonian. The quantum kinetic equations for the single particle Green’s functions of electrons and holes are self-consistently coupled to Poisson’s equation, including intercarrier scattering on the Hartree level. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self-consistent Born approximation of the scattering self-energies. Photogeneration of carriers is described on the same level in terms of a self-energy derived from the standard dipole approximation of the electron-photon interaction. Results from a simple two-band model are shown for the local density of states, spectral response, current spectrum, and current-voltage characteristics for generic single quantum well systems.