In this talk, I will discuss the development of an InGaAs air-bridge cell that achieved a record-high peak conversion efficiency of 32% and our recent efforts to improve performance at high power densities.

We analyze near-field thermophotovoltaic (NFTPV) systems in terms of their open-circuit voltage (Voc). Unlike previous numerical results with fluctuational electrodynamics, we introduce a simple analytic model that captures the physics of NFTPV systems and predicts performance metrics. We show that (i) operating in the near-field naturally enhances radiative recombination and that (ii) owing to photon recycling and minimal radiation leakage, NFTPV systems can be much thinner compared to typical PV cells, thus reducing non-radiative losses. Combination of these effects leads to values of Voc that can approach the radiative limit.

Thermophotovoltaic (TPV) devices convert thermal energy radiated from a hot emitter directly into electrical energy without any moving parts and are promising for many applications. However, current TPV devices suffer from poor efficiency stemming from inadequate spectral engineering of thermal photons. Here, we approach this challenge from a quantum route. Quantum description of thermal emitters requires non-Hermitian physics which allows powerful design tools, phase, symmetry, and topology. We demonstrate bright, directional, and large spectral contrast in thermal emission achieved by the non-Hermitian design, and thus enabling efficient TPV conversion.