Two-Terminal Monolithic In0.5Ga0.5P/GaAs Tandem Solar Cells with a High Conversion Efficiency of Over 30%

Abstract

A world-record efficiency of 30.28% has been attained for two-terminal monolithic In_0.5Ga_0.5P/GaAs tandem solar cells under one-sun air-mass 1.5 global illumination. The cell area has a practical size of 4 cm². At first, high efficiency In_0.5Ga_0.5P single junction cells had been developed by improving the minority carrier lifetime. Second, the GaAs single junction cells had been investigated to obtain higher open-circuit voltage. Third, the tandem cell performance had been improved by using an InGaP tunnel junction with AlInP barriers which constitute a double-hetero structure and increase the peak current of the tunnel junction. In addition, the AlInP barrier located beneath the InGaP top cell have been found to be effective for reflecting minority carriers in the top cell and for suppressing the diffusion of zinc from the highly doped tunnel junction toward the top cell during epitaxial growth.