Phonon-coupling enhanced absorption of alloyed amorphous silicon for solar photovoltaics

Using the observed temperature dependence of a-Si:H photon absorption spectrum and the weak-phonon interaction second-order transition theory, phonon-coupling enhanced photon absorption is predicted for a-Si-Ge and a-Si-Sn alloys. The ab initio calculated electron and phonon properties of the alloyed amorphous phase show minimally altered electronic states and significant redshifted phonon energies. This phonon shift enhances the optical phonon-coupled photon absorption resulting in increased current generation near the optical band edge. We find that this enhancement favors low-energy optical-phonon modes, thus making the soft-bond forming Sn the choice alloying element.