Highly Efficient Self-Trapped Exciton Emission of a (MA)4Cu2Br6 Single Crystal

Abstract

Recently, low-dimensional organic-inorganic lead halide perovskites have attracted much attention due to the outstanding tunable broadband emissions, while the toxicity of lead hinders their further applications in the photoelectric field. Here, we reported a novel lead-free Cu(I) based organic-inorganic perovskite-related material of (MA)4Cu2Br6 single crystal with a zero-dimensional (0D) clusters, which is a unique Cu2Br64- corner-shared tetrahedron dimer structure consisting of two connected tetrahedrons. The single crystal displays a bright broadband green emission with a high photoluminescence with quantum yield up to 93%, a large Stokes shift and very long (microsecond) PL lifetime, resulting from self-trapped excitons emission. The direct band gap characteristic of (MA)4Cu2Br6 was proved by density functional theory calculation, and its band gap was determined by experiments to be about 3.87 eV. In the temperature range of 98-258 K, the PL intensity increases gradually with the rising temperatures due to the deep-trapping out of strong electro-phonon coupling, while the PL goes down when the temperature increases over 258 K due to the phonon scattering. Deserve to mention, this new material has high chemical and light stability, in contrasting to the lead perovskite.