Influence of Heat Treatment on Phase Segregation in Polymer-Containing CsPbBr2I Composite Films

The influence of vacuuming and annealing temperatures on the properties of composite films based on CsPbBr₂I perovskites was investigated. Partial substitution of Pb²⁺ ions with Mn²⁺ was employed, and grain boundaries were passivated using polyethylene oxide and polyvinylidene fluoride. Dimethyl sulfoxide was used as the solvent, and the films were prepared by spin-coating. The vacuuming and annealing temperatures were varied in the ranges of 60–80 and 60–90°C, respectively. Photoluminescence spectral dependences were compared to assess the effects of phase segregation and the applicability of the selected temperature conditions. It was found that the samples prepared at vacuuming and annealing temperatures of 70°C exhibited photoluminescence peaks at 616 ± 14 and 638 ± 18 nm, corresponding to CsPbBr₂I. The presence of two peaks indicates slight phase segregation, which manifests as local variations in the stoichiometric composition of the samples, resulting in Br- and I-rich regions. Nevertheless, among the studied conditions, this thermal treatment regime is optimal in terms of suppressing photoinduced phase segregation: decreasing the temperature shifts the photoluminescence band toward shorter wavelengths while increasing it leads to the formation of defective nonluminescent phases.