Fabrication of 0.6 eV Bandgap In0.69Ga0.31As Thermophotovoltaic Cells and Its System Demonstration

Thermophotovoltaic (TPV) is a promising energy conversion technology that can absorb the heat from a thermal radiator and transfer it into power. As the most significant energy converter, TPV cells need a narrower bandgap to realize a wider absorption spectrum range. In this work, the fabrication and characterization of single-junction In_0.69Ga_0.31As TPV cells with a bandgap of 0.6 eV are presented. The main structure is grown on an InP substrate through metal-organic chemical vapor deposition. Step-graded InAs_yP_1−y buffer layers are used to mitigate the dislocations by relaxing the stress induced by lattice mismatch completely. Analysis of the composition, strain relaxation, layer tilt, and crystalline quality of each layer is demonstrated using triple-axis X-ray reciprocal space mapping and transmission electron microscopy. According to the tested results, each layer is found to be nearly fully relaxed and the InGaAs active layer grown on the buffer displays a high crystal quality. External quantum efficiency achieves 90% at 1100–1500 nm. Additionally, a TPV test platform is constructed to evaluate the cell performance. The maximum efficiency of the lattice-mismatched TPV cell reaches 21.92% operating at a power density of 267.4 mW cm⁻² and an emitter temperature of 1200 °C.