First‐Principles Calculation Design for 2D Perovskite to Suppress Ion Migration for High‐Performance X‐ray Detection

Abstract Ion migration is a key root‐cause of photocurrent instability in perovskite X‐ray detectors. Although 2D perovskite single crystal (PSC) is a good candidate to suppress ion migration compared with its 3D counterpart, its intrinsic stability still needs to be improved. In this work, it is first envisioned to conquer the ion migration by enhanced chemical bonding; the proposal is further confirmed by density functional theory calculations, in which the bonds are made stronger by introducing a fluorine atom into the ortho position of phenethylamine (o‐F‐PEA) to shorten the distance between adjacent organic cations in the crystal lattice for enhanced electrostatic interactions between the F atom and the neighboring benzene ring. It is further demonstrated experimentally that the activation energy for ion migration (AEIM) of (o‐F‐PEA) 2 PbI 4 PSC is increased compared with that of (PEA) 2 PbI 4 PSC. The improved AEIM is also confirmed by enhanced thermal stability. Consequently, the dark current in the (o‐F‐PEA) 2 PbI 4 2D PSC X‐ray detectors is reduced by two times compared with the (PEA) 2 PbI 4 reference. Furthermore, the detector shows the sensitivity of 1724.5 μC Gy air −1 cm −2 at 1250 V mm −1 , and much improved photocurrent stability.