Temperature-Dependent Recombination Dynamics in BH/ZnBr₂ Co-Doped CsPbI₃ Thin Films

Abstract

Temperature-dependent photoluminescence (PL), time-resolved photoluminescence (TRPL), and X-ray photoelectron spectroscopy (XPS) measurements were employed to investigate the recombination dynamics and defect evolution in BH/ZnBr₂ co-doped CsPbI₃ thin films. The results show that moderate co-doping effectively suppresses trap-assisted non-radiative recombination and improves the structural stability of the perovskite films. In particular, the optimally doped BH-Zn-23.0 sample exhibits a relatively low and weakly temperature-dependent monomolecular recombination rate constant (k₁), together with reduced exciton binding energy and suppressed exciton–phonon coupling, indicating improved defect passivation and reduced lattice disorder. In contrast, excessive ZnBr₂ incorporation leads to a pronounced increase in k₁ with increasing temperature, suggesting the activation of deep-level defect-assisted recombination pathways. A clear change in the temperature dependence of k₁ is observed near 140 K for the heavily doped sample, implying the existence of a critical doping threshold associated with defect activation and structural instability. Furthermore, the optimized co-doped films exhibit enhanced ambient phase stability, maintaining the black phase for extended storage in air. These results demonstrate that the carrier recombination behavior and environmental stability of BH/ZnBr₂ co-doped CsPbI₃ are strongly governed by the temperature-dependent evolution of defect states. This work provides insight into the role of co-doping in regulating defect-assisted recombination processes in inorganic perovskite thin films.