Enhancement of open-circuit voltage in InGaP solar cells grown by solid source molecular beam epitaxy

Abstract

The growth of ternary InGaP alloys is often susceptible to atomic ordering, which can lead to an anomalous bandgap reduction as well as the formation of antiphase boundaries (APBs). In this study, we report on the effect of growth rate and growth temperature on the performance of lattice-matched In0.52Ga0.48P solar cells grown on GaAs(001) substrates miscut 2° toward (111)B by solid-source molecular beam epitaxy. The bandgap of the InGaP film was widened from 1.855 eV for a film grown at 480 °C and 1.0 µm/h to 1.880 eV for a film grown at 510 °C and 1.5 µm/h owing to the suppression of atomic ordering in the alloy. In terms of solar cell performance, the open-circuit voltage was improved from 1.243 to 1.311 V by increasing the growth temperature and the growth rate due to not only the widening Eg but also the improved electrical characteristics (due to the fewer APBs present). In addition, the decreased number of APBs improved the fill factor and short-circuit current density. Consequently, the highest η of 14.43% was obtained for an InGaP single-junction solar cell grown at 510 °C and 1.5 µm/h and that of 25.57% for a dual-junction InGaP/GaAs solar cell.