Optoelectronic analysis of spectrally selective nanophotonic metafilm cell for thermophotovoltaic energy conversion

This work theoretically studies a spectrally selective nanophotonic cell based on an asymmetric Fabry-Perot resonance cavity structure with sub-100-nm GaSb layer for improving the thermophotovoltaic (TPV) energy conversion performance. The simulated spectral property of the ultrathin metafilm cell structure exhibits a high absorption peak above the bandgap due to the interference effect with electromagnetic field enhanced inside the GaSb layer between top and bottom silver electrodes, while the sub-bandgap absorption is as low as a few percent because of high reflectivity of the metal. An absorption enhancement nearly 20 times at particular frequency above bandgap is achieved within the sub-100-nm GaSb layer with the nanophotonic cell structure compared to the free-standing one. Besides, a thin layer of MoO_x is incorporated into the metafilm cell structure as a hole transport layer to consider the charge collection in practice. With rigorous optoelectronic analysis by considering both radiative and nonradiative recombinations (Shockley-Read-Hall and Auger), the nanophotonic cell is predicted to achieve a TPV efficiency of 22.8% and output power of 0.62 W/cm² with a black emitter at 1500 K due to spectrally enhanced in-band absorption and low sub-bandgap absorption. With an ideal selective emitter the efficiency can be further improved to 28% by eliminating sub-bandgap photons. While selective emitters still endure the challenges in perfect spectral emittance and high-temperature stability in practice, the proposed wavelength-selective nanophotonic metafilm cell could be a viable route to achieve high-efficiency and low-cost TPV energy conversion.