Combining photon recycling and concentrated illumination in a GaAs heterojunction solar cell

GaAs single-junction solar cells with rear-side-reflective structures have been developed aiming for an increase in open-circuit voltage Voc by the combination of photon recycling and concentrated illumination of sunlight. Photon recycling gains importance with increasing sunlight concentration as the materials are increasingly dominated by radiative recombination. At the same time, resistive losses because of current transport must be addressed and minimized to achieve high performances. We report here on the development of a GaAs heterojunction solar cell which was optimized for operation under concentrated sunlight. An efficiency of 28.8% is achieved at 182 suns concentration, showing a Voc of 1230 mV. This is an increase of 28 mV compared with a cell without a highly reflective back mirror. The results confirm the theoretically predicted positive effect of photon recycling under high concentration levels.