Enhanced Photon Utilization in Single Cavity Mode Air-Bridge Thermophotovoltaic Cells

An air-bridge thermophotovoltaic (TPV) cell can enable nearly complete utilization of out-of-band (OOB) photons. However, the air-bridge consists of a micron-thick free-standing semiconductor membrane that can buckle during fabrication. Such a buckled membrane supports multiple optical cavity modes in the air gap between the semiconductor and the bottom, metal back surface reflector, causing up to 10% loss in OOB reflectance ( R OOB ). Here we demonstrate a single cavity mode with an extremely flat In 0.53 Ga 0.47 As TPV membrane that exhibits R OOB = 98.9 ± 0.1% under 1279 K blackbody illumination. The remaining 1.1% reflectance loss is attributed to free carrier absorption and cavity oscillations. The flat TPV cell exhibits a spectral efficiency ranging from 68.6% to 76.5% for emitter temperatures between 900 and 1500 K, which exceeds that of previous reflective TPV cells, and represents a 20–30% improvement compared to the buckled cell, leading to a power conversion efficiency of 31.7 ± 0.1% at 1279 K.