Narrow bandgap cells for far- and near-field thermophotovoltaics

Thermophotovoltaic (TPV) converters are promising devices for the conversion of heat from a variety of sources to electricity. However, many energy sources, including waste heat recovery or solar thermal processes, only provide heat at relatively low temperatures well below 1,000 °C. These require narrow bandgap photovoltaic cells to reach sufficient power density in realistic systems. Here, we present the development of two types of narrow-gap cells for conventional far-field TPVs and for near-field nanogap TPVs. Bulk junction InAs p-i-n cells are demonstrated in a nanogap TPV configuration, and a novel quantum-engineered intersubband photovoltaic cell is demonstrated in a far-field TPV configuration. Our results show the promise of narrow-gap photovoltaic cells as well as the need for further development of these types of devices.