Regulating Exciton-Phonon Coupling to Achieve a Near-Unity Photoluminescence Quantum Yield in One-Dimensional Hybrid Metal Halides.

Low-dimensional hybrid metal halides are emerging as a highly promising class of single-component white-emitting materials for their unique broadband emission from self-trapped excitons (STEs). Despite substantial progress in the development of these metal halides, many challenges remain to be addressed to obtain a better fundamental understanding of the structure-property relationship and realize the full potentials of this class of materials. Here, via pressure regulation, a near 100% photoluminescence quantum yield (PLQY) of broadband emission is achieved in a corrugated 1D hybrid metal halide C5 N2 H16 Pb2 Br6 , which possesses a highly distorted structure with an initial PLQY of 10%. Compression reduces the overlap between STE states and ground state, leading to a suppressed phonon-assisted non-radiative decay. The PL evolution is systematically demonstrated to be controlled by the pressure-regulated exciton-phonon coupling which can be quantified using Huang-Rhys factor S. Detailed studies of the S-PLQY relation for a series of 1D hybrid metal halides (C5 N2 H16 Pb2 Br6 , C4 N2 H14 PbBr4 , C6 N2 H16 PbBr4 , and (C6 N2 H16 )3 Pb2 Br10 ) reveal a quantitative structure-property relationship that regulating S factor toward 28 leads to the maximum emission.