OPTICAL-ABSORPTION IN THE WINDOW LAYER AND ITS CONTRIBUTION TO THE SPECTRAL RESPONSE OF A P-GA1-XALXAS/P-GAAS/N-GAAS SOLAR-CELL

The influence of the aluminum content on the photovoltaic performance of the p-Ga//1// minus //xAl//xAs/p-GaAs/n-GaAs structure is investigated. An enhanced high-photon-energy spectral response is observed when the window layer has a direct gap. Short-circuit currents and conversion efficiencies calculated in these devices indicate high values in the neighborhood of those obtained with a high aluminum content. This is due to the high mobilities characterizing 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.