Energy conversion efficiency limits of air-bridge thermophotovoltaic cells

The conversion of heat to electricity via thermophotovoltaics (TPVs) holds promise for providing energy storage and recovery for fully decarbonized power grid applications [1,2]. The use of an air-bridge TPV architecture provides a unique method for high energy conversion efficiency with near-perfect out-of-band (OOB) photon reflection (R_OOB) [1]. Here we design and demonstrate air-bridge TPV cells using 3-µm-thick InGaAs/InP membranes. From Fourier transform infrared analysis, the cell shows a R_OOB > 98.5% at blackbody temperatures of 915–1425K, where the OOB photon loss is less than 1% due to free-carrier absorption. The InGaAs cell shows 17–31% efficiency in this temperature range, compared to a projected maximum efficiency of 31–49%. Using TCAD numerical simulations, we reveal that the efficiency loss is primarily due to surface recombination (with a recombination velocity of 10³ cm/s). Finally, we calculate the thermodynamic efficiency limits to the energy conversion efficiency of air-bridge TPVs with different bandgaps and find that the advantage of increasing R_OOB increases with bandgap.

Reference

[1] D. Fan, T. Burger, S. McSherry, B. Lee, A. Lenert, and S. Forrest, Nature 586, 237 (2020).

[2] A. Datas, A. Lopez-Ceballos, E. Lopez, A. Ramos, and C. del Canizo, Joule 6, 418 (2022).