Zero-Vacuum-Gap Thermophotonics

Thermophotonic (TPX) devices offer a promising pathway to overcome the power density and efficiency trade-offs of thermophotovoltaics (TPVs) by using biased light-emitting diodes (LEDs) as active infrared photon emitters. However, practical implementation of TPXs has been limited by stringent demands requiring the LED to operate at high temperatures, as well as the need for near-perfect external quantum efficiency (EQE) to enable self-sustaining (i.e., no external power supply) operation. Here, we introduce a zero-vacuum-gap thermophotonic (zTPX) architecture that integrates a high-refractive-index solid-state spacer between the LED and the photovoltaic cells, which forms an optical cavity that minimizes index mismatch and enables high photon concentration. This design enhances both power density and efficiency, over 40-fold power improvement, and up to doubled efficiency enhancement compared to conventional far-field TPX, allowing the operation of TPXs at relatively lower temperatures, at which high-performance LEDs are available. Furthermore, we show that the zTPX structure achieves a record-breaking EQE of approximately 98%, which enables a self-sustaining TPX circuit with a sizable power output. These combined performance gains position zTPX as a highly practical thermophotonic solution for thermal energy conversion and utilization at low to moderate temperatures (<1000 °C), including industrial waste-heat recovery, distributed power generation, and portable heat-to-electricity converters.