Speaker
Description
The search for novel semiconductors with sub-1 eV bandgaps is critical for efficient infrared photon-to-electricity conversion from high-temperature thermal emitters in thermophotovoltaic (TPV) systems. Double perovskites with the general formula A₂B′B″X₆ offer exceptional chemical tunability, making them attractive for targeted infrared bandgap engineering. For TPV devices operating with emitter temperatures in the 1100 - 1500 K range, the optimal bandgap lies between 0.6–0.75 eV, enabling spectral matching while minimizing thermalization losses.
Experimental studies of lead-free halide double perovskites report bandgaps in the ~1.8–1.9 eV range, well above the TPV-optimal window. These materials also exhibit relatively low mobilities compared to lead-halide perovskites; for example, Cs₂AgBiBr₆ thin films have a lower bound of ~1 cm² V⁻¹ s⁻¹, while single crystals can reach ~11.8 cm² V⁻¹ s⁻¹. Given that both optimal bandgap positioning and balanced carrier transport are intrinsic design criteria for high-efficiency TPV converters, we conducted a computational screening of candidate double perovskites. Using density functional theory (VASP), Boltzmann transport modeling with AMSET, and structural data from the Materials Project API, we screened Cs₂CuSbCl₆, Cs₂SnBr₆, and Cs₂CuSbBr₆. The computed bandgaps closely matched literature values, validating our approach and indicating that Cs₂CuSbBr₆ is the most promising candidate. High-throughput calculations were then performed to systematically vary the halide composition in the Cs₂CuSb(BrₓI₆₋ₓ) series.
Fully iodide-substituted Cs₂CuSbI₆ exhibits a direct bandgap of 0.683 eV, squarely within the TPV-efficient range. The evolution of bandgap with halide substitution, the temperature-dependent transport properties for the full halide series at nₕ = 10¹⁶ cm⁻³ , and the carrier mobilities calculated via AMSET will be demonstrated. While factors such as Auger recombination and phase stability are essential for practical implementation, this study will provide an initial screening for the batch of candidate materials that deserve future experimental investigations.
