Relativistic electronic structure and photovoltaic performance of K2CsSb

Abstract

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.