Fig. 4.

Photo-stability of the perovskites exhibited strong temperature dependence. a The calculated ΔG_light indicates that, under strong illumination, the perovskite in the composites would be less photo-stable as the temperature reduces from 297 K to 200 K. The vertical dash lines correspond to the compositions of samples examined experimentally in b–d. b–d Photoluminescence spectra of CsPb(Br_xI_1-x)₃/Cs₄Pb(Br_xI_1-x)₆ composites with X_Br = 0.7 (b), X_Br = 0.5 (c) and X_Br = 0.4 (d) were measured at temperatures from 150 K to 290 K (increase T). Reduced photo-stability, indicated by further split of photoluminescence peaks, was observed at lower temperature in b and c. The sample with higher iodine concentration in d (X_Br = 0.4) remained consistently stable across the entire temperature range, consistent with other measurements where I-rich perovskites appeared generally more photo-stable. The grey circles in b–d show the peak positions determined by fitting the measured photoluminescence spectra. b–d share the same color scale as shown in c