The Effect of Halide Composition on the Luminescent Properties of Ternary Cesium–Copper Halide Pseudo‐Perovskite Films

Abstract

Ternary copper halide pseudo‐perovskites are in the forefront of research as potential active materials in light emission applications. The optoelectronic properties of these compounds can be fine‐tuned by the preparation of mixed‐halide compositions. After irradiation, self‐trapped excitonic states are formed in these materials. However, the emission from these self‐trapped states is not yet fully understood. In this work, mixed‐halide Cs3Cu2X5 films (where X: I and/or Br) are prepared by a simple spray‐coating method. Using ultraviolet photoelectron spectroscopy, the changes in optoelectronic properties are linked to the electronic structure of these materials. It is revealed that the incorporation of bromide into the lattice makes the emission process of these materials more vulnerable to trap states. By combining the different spectroscopic characterization techniques, the exact band structure of these compounds is determined, and the different processes are translated to the absolute energy scale. As an alternative excitation mechanism of self‐trapped states, α‐particles are used to induce radioluminescence response. The Cs3Cu2X5 films exhibit composite decay patterns, most likely attributed to a multitude of different trap state‐mediated recombination processes.

All-inorganic copper-halide perovskites for large-Stokes shift and ten-nanosecond-emission scintillators

“…49 This, in turn, manifests in the large SS and multiple STE emissions as outlined by previous works. 29,34,90,94 We believe that such STE modulation not only improves τ 1 but simultaneously reduced the slowest τ 3 proportion significantly (see Table 2). This rationalizes the QY results shown in Table 3 of the reported CHPs by a mechanochemical approach.…”

“…Such bond length and angle reduction in 0D CHPs signify the fact that our attempt to incorporate Br atoms onto the CHP host lattice affects the proportion ratio between the well-known three STE configurations. 92,93 Since the first decay component of lifetimes ( τ 1 ) is associated with the direct recombination of excitons, 74,93,94 we argue that the [Cu 2 X 5 ] 3− species in the mixed halide system (I : Br 4 : 1 and 3 : 2) powders have a slightly distorted structure compared to their conventional 0D Cs 3 Cu 2 I 5 . This eventually decreased the perovskite volume, mitigating the depth of traps that are largely found in bromine-rich CHPs.…”

“…This eventually decreased the perovskite volume, mitigating the depth of traps that are largely found in bromine-rich CHPs. 94 In addition, we postulate that the Jahn–Teller distortion in the d orbital of Cu centres is strongly enhanced when the unequal occupation of the other degenerate t 2g 3d orbitals is indirectly affected by their interaction due to Br incorporation. 49 This, in turn, manifests in the large SS and multiple STE emissions as outlined by previous works.…”