The use of selectively reflective photovoltaic cells in thermophotovoltaic energy systems enables the recovery of otherwise unusable low energy (out-of-band) photons, thereby increasing the power conversion efficiency of the technology. We recently developed a thin-film cell architecture with a nanoscale air cavity buried beneath the light-absorbing InGaAs layer [1]. This cell exhibits ~98.5% out-of-band (OOB) reflectance, enabling conversion efficiencies exceeding 32% under illumination by ~1450 K SiC emitter. To investigate the performance of this device at different emitter temperatures (or power densities), we characterize the cell under various conditions characteristic of high thermal load [2]. We also quantify the loss pathways (including but not limited to Ohmic losses, thermalization losses, non-radiative recombination and OOB losses) associated with varying emitter temperatures. In this work, we propose two distinct cell configurations that further leverage the unique air-bridge architecture to overcome several challenges associated with operation of TPV cells at varying temperatures. First among these configurations is a double airbridge tandem cell, which leverages the top and bottom Au grid lines to optically and electronically connect the sub cells, thereby eliminating the need for a conventional tunnel junction. This may help to mitigate some of the primary loss pathways, including Ohmic and thermalization losses. Finally, we describe an alternative approach to photon recuperation, in which a transparent cell allows transmission of unusable photons to a secondary emitter, thereby further eliminating the OOB loss characteristic of reflective cells [3]. Here, the use of the air-bridge architecture uniquely enables transfer of the thin-film epilayer to a transparent device substrate.
REFERENCE
[1] D. Fan, T. Burger, S. McSherry, B. Lee, A. Lenert, and S. R. Forrest, “Near-perfect photon utilization in an air-bridge thermophotovoltaic cell,†Nature, vol. 586, no. 7828, pp. 237–241, 2020, doi: 10.1038/s41586-020-2717-7.
[2] B. Roy-Layinde et al., “Sustaining efficiency at elevated power densities in InGaAs airbridge thermophotovoltaic cells,†Solar Energy Materials and Solar Cells, vol. 236, p. 111523, 2022, doi: https://doi.org/10.1016/j.solmat.2021.111523.
[3] T. Burger, B. Roy-Layinde, R. Lentz, Z. J. Berquist, S. R. Forrest, and A. Lenert, “Semitransparent thermophotovoltaics for efficient utilization of moderate temperature thermal radiation,†Proceedings of the National Academy of Sciences, vol. 119, no. 48, p. e2215977119, 2022, doi: 10.1073/pnas.2215977119.
