High-efficiency monolithic InGaP/GaAs tandem solar cells with improved top-cell back-surface-field layers

Improved back-surface-field (BSF) layers have been adapted for the top cell of a two-terminal, monolithic InGaP/GaAs dual-junction cell in order to recover the top-cell quantum efficiency, which had been reduced significantly by the diffusion of zinc from the p/sup +/-InGaP BSF into the top-cell base layer. A thick p/sup +/-InGaP layer and a thin p-AlInP layer have proved to be effective in improving the top-cell quantum efficiency, especially in the long-wavelength region. Although the current-matching between the top- and bottom-cells was not complete, tandem cells with those BSF layers obtained high conversion efficiencies of 27.3% and 26.4%, respectively.