GeSn alloys for thermophotovoltaics: interplay of heat transfer, optical and electronic properties

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The growing urgency to address pollution and climate change has intensified efforts to find alternative ways to generate power and improve existing technologies. Traditional thermodynamic systems, particularly those that rely on converting heat into mechanical energy, often suffer from efficiency losses. By contrast, thermophotovoltaics (TPV) offer a promising way to convert heat directly into electricity with fewer intermediate steps. TPV systems can harvest thermal energy from concentrated sunlight or recover waste heat from conventional power plants, providing a compact solution for terrestrial, remote and space-based applications. In this study, we present a comprehensive finite element model (FEM) of a TPV system that uses a low-bandgap, direct-gap GeSn photovoltaic cell. GeSn is a group-IV, CMOS-compatible semiconductor, whose use in optoelectronics has boomed in recent years thanks to crystal growth development. For application to TPV, our model considers indirect recombination processes, multilayer generation dynamics and thermal equilibrium between the emitter and cell. For a basic cylindrical geometry, the simulation predicts up to 6.5% power conversion efficiency at 0.11 W/cm 2 power generated and an optimal temperature of around 1100 K. We also investigate strategies for improving device efficiency, such as the use of selective emitters. This modelling framework enables in-depth theoretical exploration of Ge-based materials under varying strain, composition and temperature, toward the design of next-generation optoelectronic and energy harvesting devices.