Mechanically rigid 2D lead halide perovskite (PMA)2PbCl4 with pressure-stable broadband emission

Abstract

We present a combined experimental and theoretical investigation of the pressure response of the chlorine-based two-dimensional perovskite (PMA)₂PbCl₄. High-pressure synchrotron powder X-ray diffraction (HP-PXRD), photoluminescence spectroscopy (HP-PL), and density functional theory (DFT) calculations reveal that compression up to 5.45 GPa induces pronounced anisotropic lattice contraction and partial amorphization, while decompression reveals phase reversibility. The PbCl₆ octahedra remain mechanically rigid, with distortions accommodated by octahedral tilts, flattening, and migration of phenylmethylammonium cations (PMA⁺), leading to interlayer planarization and enhanced electron–phonon coupling. Elastic tensor analysis confirms moderate mechanical anisotropy and coexisting auxetic and conventional elastic responses. HP-PL demonstrates a pressure-driven crossover between narrow free-exciton emission (quenched by 1.84 GPa) and more resilient broadband self-trapped exciton emission (persisting up to 7.8 GPa with its maximum intensity at ∼4.5 GPa). Overall, the compression-driven structure–property evolution maintains broadband emission, which leads to increased nonradiative losses at higher pressures. The combined results establish (PMA)₂PbCl₄ as a mechanically robust, pressure-tunable broadband emitter with strong potential for stable optoelectronic applications.