Dual Self-Trapped Exciton Emission with Ultrahigh Photoluminescence Quantum Yield in CsCu2I3 and Cs3Cu2I5 Perovskite Single Crystals

Low-dimensional metal halide perovskites possessing a large exciton binding energy have shown great promise in achieving efficient photonic emission required in the fields of lighting sources and display. Here, efficient dual self-trapped exciton (STE) emissions are directly observed in a low-dimensional inorganic copper iodine quasi-perovskite single crystal. The dual STEs have natural structure-oriented performance, showing a strong electron–phonon coupling. Temperature-dependent PL spectra and Raman spectra demonstrate a thermal-assisted radiative recombination of dark STEs, and based on such a mechanism, an ultrahigh photoluminescence quantum yield (PLQY∼100%) was obtained in bulk crystals with a zero-dimensional electronic structure, favoring photoexcited STEs to gain a large binding energy of up to 563 meV. All these results above show a great advancement in high-efficiency photonic emission through the low-dimensional electronic structure and STE radiative recombination.