High-Temperature Polarization-Free III-Nitride Solar Cells with Self-Cooling Effects

High-temperature photovoltaics (PV) for terrestrial and extraterrestrial applications have presented demanding challenges for current solar cell materials, such as Si, III-V AlGaInP, and II-VI. Wide-bandgap III-nitride materials, in contrast, offer several intrinsic advantages that make them extremely appealing for high-temperature applications. In this study, we fabricated and characterized III-nitride solar cells using polarization-free (i.e., nonpolar) InGaN/GaN multiple quantum wells (MQWs). The InGaN solar cells showed a large working temperature range from room temperature (RT) to 450 °C, with positive temperature coefficients up to 350 °C. The peak external quantum efficiencies of the devices showed a 2.5-fold enhancement from RT (∼32%) to 450 °C (∼81%), which is distinct from all other solar cells ever reported. This can be partially attributed to an increase of over 70% in carrier lifetime in nonpolar InGaN MQWs obtained from time-resolved photoluminescence. Furthermore, a thermal radiation analysis revealed a unique self-cooling effect for III-nitride materials, which also helps enhance device performance at high temperature. These results offer new insights and strategies for the design and fabrication of high-efficiency high-temperature PV cells.