Tailoring Polaron Dimensions in Lead‐Tin Hybrid Perovskites

Abstract Charge carriers in the soft and polar perovskite lattice form so‐called polaron quasiparticles, charge carriers dressed with a lattice deformation. The spatial extent of a polaron is governed by the material's electron‐phonon interaction strength, which determines charge carrier effective mass, mobility, and the so‐called Mott polaron density, that is, the maximum stable density of charge carriers that a perovskite can support. Despite its significance, controlling polaron dimensions has been challenging. Here, experimental substantial tuning of polaron dimensions is reported by lattice engineering, through Pb/Sn substitution in CH 3 NH 3 Sn x Pb 1−x I 3 . The polaron dimension is deduced from the Mott polaron density, which can be composition‐tuned over an order of magnitude, while charge carrier mobility occurs through band transport, and remains substantial across all compositions, ranging from 10 s to 100 s cm 2 V s −1 at room temperature. The effective modulation of polaron size can be understood by considering the bond asymmetry after carrier injection as well as the random spatial distribution of Pb/Sn ions. This study underscores the potential for tailoring polaron dimensions, which is crucial for optimizing applications prioritizing either high charge carrier density or high mobility.