Conformational ordering in two-dimensional (PEA)2PbBr4 single crystals driven by thermal annealing

Abstract

Along with their improved stability and tunable quantum well structures, two-dimensional (2D) perovskites have become potential candidates for developing high-efficiency optoelectronic devices, while the atomic configuration of the materials governs their optoelectronic properties. In this work, direct experimental evidence for conformational ordering in 2D (PEA)2PbBr4 single crystals driven by thermal annealing was obtained. Upon post-annealing at 160 °C, an ordered phase with a larger d-spacing emerges, which was unambiguously confirmed by x-ray diffraction patterns. The organic cations exhibit a perpendicular orientation relative to the 2D plane, as evidenced by the infrared-active C–C stretching mode. In addition, the reduced in-plane anisotropy of two-photon excited photoluminescence indicates that the tilting of [PbBr6]4− octahedra in the inorganic layers was suppressed after post-annealing. The observed structural ordering induced by thermal annealing furnishes important scientific support for the application of 2D perovskites in optoelectronic devices.