The depletion layer collection efficiency for p-n junction, Schottky diode, and surface insulator solar cells

The collection efficiency for carriers optically generated in the depletion region of photovoltaic solar cells is analyzed. For p-n junction devices, it is shown that virtually all these carriers are collected provided the minority carrier diffusion lengths are larger than the width of the depletion layer, and that a reasonable percentage will be collected even when the diffusion lengths are much smaller than this. For Schottky diode devices, the collection efficiency for carriers optically generated near the metal-semiconductor interface is shown to be small and to depend critically upon the exact model of the contact used. As a consequence the spectral response of Schottky diodes at short wavelengths is shown to contain considerable information regarding the physics of the metal-semiconductor contact. New surface insulator devices are shown to have a short-wavelength response superior to that of Schottky diodes.