Towards high power density, high efficiency thermophotovoltaic energy conversion system in the near field

Solid-state energy conversion holds promise for efficient extraction of electricity from different heat sources like solar and industrial waste heat. In particular, thermophotovoltaic (TPV) system involves a hot emitter radiating photons that excite electron hole pairs in a photovoltaic (PV) cell. Most TPV architectures in the far-field demonstrate very low power densities. Several theoretical proposals have shown that dramatic enhancement in power density can be achieved by reducing the gap to tens of nanometers where evanescent waves start contributing to power transfer. However, such demonstrations have been elusive due to the challenge of maintaining nano separations between a hot emitter (~1000 K) and a cold cell (~300 K). Here, we will first describe how high resolution calorimetry and custom-built nano-positioning platform have made possible, the first demonstration of ~40 fold increase in the power output, compared to far field, when the gap between the PV cell and thermal emitter at 650 K is reduced from ~10 µm to 60 nm. Further, we will describe ongoing efforts to achieve increases in both power output and efficiencies by engineering emitters that can reach high temperatures.