Optical absorption in the window layer and its contribution to the spectral response of a pGa1-x Alx As/p-GaAs/n-GaAs solar cell

The influence of the aluminium content on the photovoltaic performance of the p-Ga1¿xAlxAs/p-GaAs/n-GaAs structure is investigated. An enhanced high-photon-energy spectral response is observed when the window layer has a direct gap. Also short-circuit currents and conversion efficiencies calculated in these devices indicate high values in the neighbourhood of those obtained with a high aluminium content. This is due to the high mobilities characterising direct valley electrons; i.e. the contribution of the window layer to the cell current is greatly enhanced, to the extent that the increased photogeneration in this layer does not lead to any significant loss.