Relativistic electronic structure and photovoltaic performance of K₂CsSb

The discovery of an efficient and cost-effective photovoltaic absorber is urgently needed to meet global emission targets. Antimony-based materials have emerged as promising non-toxic and earth-abundant candidates with similar electronic properties to the lead hybrid perovskites. The full-Heusler K2CsSb has been widely studied as a photocathode and thermoelectric material but has not been evaluated as a potential photovoltaic absorber. Here, using relativistic hybrid density functional theory, we demonstrate that K2CsSb exhibits ideal properties for use in photovoltaic applications, based on its bandgap, dispersive conduction band, and strong optical absorption. Using a detailed balance approach, we reveal the maximum theoretical efficiency to be competitive with other state-of-the-art photovoltaics, reaching over 28 percent at a thickness of 200 nm. Additionally, we perform band-alignment calculations to provide recommendations for suitable device architectures that will minimise contact losses.