Investigation of High-Efficiency InGaP/GaAs Tandem Solar Cells under Concentration Operation

The photovoltaic properties of InGaP/GaAs tandem solar cells under concentration have been investigated for concentration application. A high efficiency of 31.2% has been obtained for the InGaP/GaAs tandem solar cell under 5.1 suns of AM1.5 illumination. However, as the light intensity further increases, the efficiency is limited due to the reduction in the fill factor. The results show that not only very high peak current density, J p, of the tunnel diode but also the valley current density, J v, of the tunnel diode is necessary for high concentration. The efficiency predictions of the InGaP/GaAs tandem cell based on a numerical analysis suggest that a conversion efficiency of over 35% will be obtained at 500 suns if the series resistance of less than 0.001 Ω/cm2 is realized. Photocurrent mismatch between the top and bottom cells during high-temperature operation has also been analyzed for the design of concentrator cells.