Analysis of air-bridge thermophotovoltaic devices and systems

We present a model of air-bridge InGaAs and Si thermophotovoltaic (TPV) systems that guides the optimization of both output power density and efficiency, considering key design factors such as series resistance (R_s), shunt resistance, out-of-band reflectance, and dissipated power. Assuming lossless emitter-to-cell coupling, an InGaAs TPV cell can reach an efficiency of 43.2 % and output power density (P_out) = 1.6 W/cm² at an emitter temperature of T_h = 1060 °C. At T_h = 1500 °C, P_out can exceed 9 W/cm², although ohmic losses may reduce the efficiency to below 35 %. In contrast, Si air-bridge TPVs exhibit relatively high parasitic power losses due to free carrier absorption (FCA), limiting the efficiency to 30.1 % at T_h = 1400 °C. By suppressing FCA, this efficiency can be improved to 40 %. However, the high R_s of Si TPV cells restricts P_out to <2 W/cm², suggesting that Si-based TPV systems may not be suitable for high-power applications. While this model has been used for InGaAs and Si TPVs, its versatility allows for optimizing the performance of TPV systems with other semiconductor materials and device structures.