Extending the Leverage of Air-Bridge Thermophotovoltaic Architecture: Design, Modeling, and Experimental Demonstration

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A low-bandgap III-V thin-film thermophotovoltaic (TPV) system utilizes heat for energy conversion to electricity. Photon recycling enabled by an air cavity at the back of a TPV membrane boosts the conversion efficiency. However, the vulnerability of thin-film membranes to buckling and cracks constrains uses of an air-mirror thin-film TPV architecture. In this thesis, the engineering of an InGaAs III-V TPV cell is explored based on mathematical solutions, computer simulations, and experiment. The first part of this thesis presentation addresses controllable buckled epitaxial thin-film membranes and provides solutions for non-buckled materials. The second part introduces a non-buckled InGaAs/InP heterojunction photodiode membrane. An experimental demonstration reports a 30.2% power conversion efficiency (PCE) and 97.9% out-of-band reflectance under a 1350-K heat emitting source. In the third section, a two air-cavity multi-junction TPV architecture is presented, which conceptually promises a wide range of materials combinations useful in tandem architectures without requiring lattice-matched epitaxial growth between sub-cells. As a demonstration, an InGaAs-based tandem TPV cell achieves a higher open-circuit voltage compared to a single-junction cell. In the final part, the extrinsic loss mechanism in a practical InGaAs-based TPV cell is determined, indicating that a single-junction TPV device can realize a power conversion efficiency exceeding 40%.

Chair: Professor Stephen R. Forrest