Large Area Near-Field Thermophotovoltaics for Low Temperature Applications

Thermophotovoltaics, devices that convert thermal infrared photons to electricity, offer a key pathway for a variety of critical renewable energy technologies including thermal energy storage, waste heat recovery, and direct solar-thermal power generation. However, conventional far-field devices struggle to generate reasonable powers at lower temperatures. Near-field thermophotovoltaics provide a pathway to substantially higher powers by leveraging photon tunneling effects. Here a large area near-field thermophotovoltaic device is presented, created with an epitaxial co-fabrication approach, that consists of a self-supported 0.28 cm2 emitter-cell pair with a 150 nm gap. The device generates 1.22 mW at 460 degrees C, a 25-fold increase over the same cell measured in a far-field configuration. Furthermore, the near-field device demonstrates short circuit current densities greater than the far-field photocurrent limit at all the temperatures tested, confirming the role of photon tunneling effects in the performance enhancement. Modeling suggests several practical directions for cell improvements and further increases in power density. These results highlight the promise of near-field thermophotovoltaics, especially for low temperature applications.