Cysteine-Based Hybrid Perovskite Exhibiting Thermally Tunable Dual-Band Photoluminescence

Broadband light-emitting hybrid perovskites are promising for solid-state lighting and display technologies, yet stable single-phase lead iodide hybrid perovskites combining intrinsic broadband emission with reversible chromaticity tuning remain scarce. Herein, we report the amino acid-based two-dimensional organic-inorganic lead iodide perovskite (l-cysH)PbI3·H2O, derived from l-cysteine, which exhibits reversible temperature-dependent emission-color tuning. The compound is a semiconductor with an optical band gap of 2.53 eV and displays dual-channel broadband photoluminescence across the visible region under UV excitation. Upon cooling from 238 to 78 K, the emission changes from yellowish-white (CIE: 0.342, 0.399) to a warmer, more saturated emission (CIE: 0.385, 0.473), while the integrated photoluminescence intensity increases approximately 27-fold. The emission comprises a narrow high-energy band attributed to free-exciton recombination and a broad lower-energy band tentatively assigned to self-trapped excitons. Arrhenius analysis yields an activation energy of 72.3(12) meV, indicating thermally activated quenching. Density functional theory calculations reveal an indirect fundamental band gap and strongly anisotropic charge transport, consistent with the layered structure. These results demonstrate thermally tunable broadband emission in a single-phase 2D amino acid-based lead iodide perovskite without halide mixing, extrinsic luminescent dopants, or multiphase engineering.