Exciton–phonon coupling in two-dimensional layered (BA)2PbI4 perovskite microplates

Abstract

Two-dimensional layered (BA)₂PbI₄ (BA = C₄H₉NH₃) perovskites are emerging as a new class of layered materials and show great potential in optoelectronic applications. Elucidating how exciton–phonon interaction affects the excitonic emission is of great importance for a better knowledge of their optoelectronic properties. In this letter, we synthesized high-quality (BA)₂PbI₄ microplates via solution methods, and dual-excitonic emission peaks (surface-emission and interior-emission) were detected from the as-grown samples at low temperatures. Furthermore, we determine the energies for the longitudinal optical phonon modes to be ∼27 and ∼18 meV, and the exciton–phonon coupling strengths to be ∼177 and ∼21 meV for the surface-emission and interior-emission bands, respectively. Compared to the interior-emission band, the stronger exciton–phonon interaction results in a considerable degree of spectral broadening and red-shift for the surface-emission with increasing temperature. In contrast, the (OA)₂PbI₄ (OA = C₈H₁₇NH₂) microplates with longer alkyl chains between Pb–I layers, exhibit only one excitonic emission peak, as well as a large exciton–phonon coupling strength. Our work clarifies the influence of exciton–phonon coupling on the excitonic emission of (BA)₂PbI₄ microplates, and also suggests the intrinsic relationship between the exciton–phonon coupling and the length of organic carbon chain ligands.