InGaN/GaN multi-quantum-well solar cells under high solar concentration and elevated temperatures for hybrid solar thermal-photovoltaic power plants

Hybrid solar electricity generation combines the high efficiency of photovoltaics (PVs) with the dispatchability of solar thermal power plants. Recent thermodynamic analyses have shown that the most efficient strategy constitutes an integrated concentrating PV-thermal absorber operating at high solar concentration and at the high temperatures suitable to efficient commercial steam turbines (~673–873 K). The recuperation of PV thermalization losses and the exploitation of sub-bandgap photons can more than compensate for the inherent decrease of PV efficiency with temperature in properly tailored tandem solar cells for which promising candidates are III–N alloys. Recently, there have been considerable efforts to develop apposite InGaN solar cells by producing InGaN/GaN multiple quantum wells (MQWs) as the top cell in a tandem PV device that would absorb the short-wavelength regime of the solar spectrum, while sub-bandgap photons and PV thermalization are absorbed in the thermal receiver. We present measurements of current–voltage curves and external quantum efficiency spectra for InGaN/GaN MQW solar cells under high sunlight intensity, up to 1 W/mm² (1000 suns) and elevated temperature, up to 723 K. We find that the short-circuit current increases significantly with temperature, while the magnitude of the temperature coefficient of the open-circuit voltage decreases with solar concentration according to basic photodiode theory. Conversion efficiency peaks at 623–723 K under ~300 suns, with no perceptible worsening in cell performance under extensive temperature and irradiance cycling—an encouraging finding in the quest for high-temperature high-irradiance cells.