Strong Electron–Phonon Coupling and Lattice Dynamics in One-Dimensional [(CH₃)₂NH₂]PbI₃ Hybrid Perovskite

Hybrid halide perovskites (HHPs) have attracted significant attention due to their remarkable optoelectronic properties that combine the advantages of low-cost, effective fabrication methods of organic–inorganic materials. Notably, low-dimensional hybrid halide perovskites including two-dimensional (2D) layers and one-dimensional (1D) chains are recognized for their superior stability and moisture resistance, making them highly appealing for practical applications. Particularly, DMAPbI₃ has attracted attention due to other interesting behaviors and properties, such as thermally induced order–disorder processes, dielectric transition, and cooperative electric ordering of DMA dipole moments. In this paper, we investigated the interplay between the low-temperature structural phase transition (SPT) undergone by the low-dimensional (1D) hybrid halide perovskite-like DMAPbI₃ and its optoelectronic properties. Our approach combines synchrotron X-ray powder diffraction, Raman spectroscopy, thermo-microscopy, differential scanning calorimetry (DSC), and photoluminescence (PL) techniques. Temperature-dependent synchrotron powder diffraction and Raman spectroscopy reveal that the modes associated with I–Pb–I and DMA+ ions play a crucial role in the order–disorder SPT in DMAPbI₃. The reversible SPT modifies its optoelectronic properties, notably affecting its thermochromic behavior and PL emission. The origin of the PL phenomenon is associated with self-trapped excitons (STEs), which are allowed due to a strong electron–phonon coupling quantified by the Huang–Rhys factor (S = 97 ± 1). Notably, we identify the longitudinal optical (LO) phonon mode at 84 cm^–1, which plays a significant role in the electron–phonon interaction. Our results show that these STEs not only intensify the PL spectra at lower temperatures but also induce a shift in the color emission, transforming it from a light orange-red to an intense bright strong red.