Inspecting the different expressions of anharmonicity in halide perovskites

Although optoelectronic devices based on halide perovskites (HaPs) have achieved outstanding performance, comparable to high-quality inorganic semiconductors, various fundamental aspects of these materials remain puzzling. One key difference to conventional semiconductors is that HaPs exhibit strong vibrational anharmonicities already at room temperature, which are known to influence several optoelectronic properties, including carrier transport and optical absorption characteristics. Here, we investigate different factors that potentially influence the vibrational anharmonicity in HaPs, using molecular dynamics based on density-functional theory. This allows for disentangling the role of A-site dynamics and its coupling to the inorganic framework. Our results help understanding the interrelations of lattice anharmonicity and bonding mechanisms in halide perovskites, possibly providing guidelines for material design.