Wave function Localization Reduces the Bandgap of Disordered Double Perovskite Cs2AgBiBr6

The Journal of Physical Chemistry Letters. 2024. Vol. 15. No. 45. P. 11268–11274.

Liu D., Bayan Amer Abzakh, Kazakova E., Dmitrii A. Abrameshin, Troshin P., Long R., Andrey S. Vasenko

Double perovskite Cs2AgBiBr6 is a promising alternative to lead-based perovskites with excellent stability and attractive optoelectronic properties. However, a relatively large bandgap severely limits its performance in many applications such as solar cells and photodetectors. It has been reported that a random distribution of Ag and Bi atoms in Cs2AgBiBr6 effectively reduces its bandgap without introducing dopants or impurities, while the mechanism remains unclear. Here, using density functional theory calculations, we demonstrate the Ag–Bi disorder in Cs2AgBiBr6 generates localized electronic states as band edges to regulate the bandgap. The disordered structures segregate Ag and Bi atoms in the lattice, and the formed homoatomic clusters lead to wavefunction localization. Moreover, the bandgap decrease exhibits a non-monotonic dependence on the degree of disorder. Our results are comparable with experimental observations and provide crucial insights into understanding the order–disorder transition in double perovskites.

Keywords: Теория функционала плотности, disordered systems, неупорядоченные системы, Density functional theory (DFT), double perovskite, двойной перовскит