Concentrated near-field thermophotonics for efficient solar energy harvesting: Model development, system analysis, and performance optimization

In recent years, research on near-field thermophotonic systems has predominantly focused on waste heat recovery and electroluminescence cooling, while studies on near-field thermophotonic converters for solar energy harvesting have not been reported. We propose a near-field solar thermophotonic converter (NFSTC) that harnesses the full solar spectrum to generate electricity. Considering fluctuational electrodynamics and nonradiative recombination losses, we developed a self-consistent model to theoretically evaluate the performance of the NF-STC system from far-field to near-field regimes under two scenarios: varying LED temperature and fixed LED temperature. In the case of variable LED temperature, we identify that increasing the solar concentration, decreasing the thickness of the semiconductor material to mitigate the effect of non-radiative recombination, narrowing the vacuum gap spacing, and implementing gold back reflector for photon recycling can significantly bolster the performance of the system. Specifically, when the gap spacing is 10 nm, and the solar concentration factor is 400, we show that the total electrical power density and overall conversion efficiency can reach 8892 mW cm-2 and 22.2%, respectively. Conversely, in the fixed LED temperature scenario, the performance characteristics diverge from those observed in the variable temperature case. The system exhibits superior performance at higher LED temperatures and smaller gap spacing. This work deepens the understanding of thermophotonic converters' application in solar energy harvesting by considering the interplay of various physical phenomena. It presents a promising pathway for efficient solar thermal power conversion.