Defect emission in Cs3Cu2I5 and CsCu2I3 halide films

Abstract

Cs3Cu2I5 and CsCu2I3 have shown potential applications as optoelectronic materials, but the mechanism of their emission remains controversial. It is widely believed that the Stokes shifts of Cs3Cu2I5 (1.45 eV) and CsCu2I3 (1.63 eV) are caused by self-trapped excitons, but the apparent changes in emission intensity observed experimentally are difficult to explain by this theory. In this paper, the defect emission mechanism is investigated: Iodine vacancies (VI) are widely present in iodide materials, but the effect of such point defects on Cs3Cu2I5 and CsCu2I3 has been little studied. Theoretical calculations based on the first-principles suggest that the VI defect (3.05 eV) may be directly related to the Stokes shift of Cs3Cu2I5 (similar conclusions were obtained for CsCu2I3). In the experiments related to VI, the emission quenching in the iodination treatment is associated with the decrease of defect concentration, while the emission recovery in the annealing treatment stems from the increase of defect concentration caused by iodine decomposition. The iodination and annealing treatments for CuI shows that VI defects play an important role in the emission of iodide. In addition, experiments to control the defect concentration by RTP treatment also showed that VI defects have an effect on the emission intensity of Cs3Cu2I5 and CsCu2I3. Based on the experimental results and theoretical calculations, the emission mechanism of Cs3Cu2I5 and CsCu2I3 may be the semiconductor defect emission theory. We believe that our research on the defect emission theory will provide new insights into the application of Cs3Cu2I5 and CsCu2I3.