NaBiS₂ as a Next-Generation Photovoltaic Absorber

I-V-VI₂ ternary chalcogenides were gaining more attention recently owing to their high air stability along with earth-abundant and nontoxic compounds. More interestingly, some of them have been predicted to be potential 'perovskite-inspired materials' that can exhibit defect tolerance. In this work, we investigated the optoelectronic properties of cation-disordered NaBiS₂ nanocrystals, which have a steep absorption onset, with absorption coefficients > 10⁵ cm^-1 just above its pseudo-direct bandgap of 1.4 eVe Surprisingly, an ultrafast photoconductivity decay and long-lived charge-carrier population almost independent of defect densities were simultaneously observed in N aBiS2 nanocrystals. Through the density functional theory calculations, these unusual features are found to be highly associated with the non-bonding S p orbitals above the upper valence band, which can be further enhanced by cation inhomogeneity. Our work hence reveals the critical role of cation disorder on both absorption characteristics and charge-carrier kinetics of I-V-VI₂ ternary chalcogenides.