(559c) Overcoming Loss Pathways in Photovoltaic Conversion of Thermal Radiation

Thermophotovoltaic generation is the conversion of thermal radiation to electrical power through the photovoltaic effect. This s a promising approach for various energy applications such as cogeneration of heat and power, thermal energy storage and waste heat recovery [1]. Utilization of selectively reflective photovoltaic cells in thermophotovoltaic energy systems enables the recuperation of otherwise unusable low energy (out-of-band) photons, thereby improving the technology’s power conversion efficiency. Recently, we created a thin-film cell architecture in which a nanoscale air cavity is buried beneath an Indium-Gallium-Arsenide (InGaAs) light-absorbing layer [2]. This cell exhibits ~98.5% out-of-band (OB) reflectance, enabling conversion efficiencies exceeding 32% under illumination by ~1450 K SiC emitter. To investigate the performance of this device at elevated power densities, we characterize the cell under various conditions characteristic of high thermal load [3]. In this work, we quantify the loss pathways in the process (including but not limited to Ohmic losses, thermalization losses, non-radiative recombination and OB losses). We then propose several cell configurations that further leverage the unique air-bridge architecture to overcome several challenges associated with operation of TPV cells at high power densities. First among these configurations is a tandem cell that avoids the use of tunnel junction (heavily doped layer that connects top and bottom cell) thereby overcoming the limitations of parasitic absorption of OB photons. This tandem cell leverages the airbridge approach where the top junction is bonded (via aligned Au-Au thermocompression bonding) to the bottom junction thereby connecting the cells electrically. This approach can lead to the minimization of some primary loss pathways such as out-of-band, ohmic and thermalization losses. Lastly, 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 OB loss characteristic of reflective cells. These improvements would help unlock the full potential of thermophotovoltaic cells as an emerging energy technology for sustainable energy generation.

REFERENCE

[1] T. Burger, C. Sempere, B. Roy-Layinde, and A. Lenert, Present Efficiencies and Future Opportunities in Thermophotovoltaics, Joule 4, 1660 (2020).

[2] 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 (2020).

[3] B. Roy-Layinde, T. Burger, D. Fan, B. Lee, S. McSherry, S. R. Forrest, and A. Lenert, Sustaining Efficiency at Elevated Power Densities in InGaAs Airbridge Thermophotovoltaic Cells, Sol. Energy Mater. Sol. Cells 236, 111523 (2022).