Evaluating the radiation tolerance and halide-dependent stability of Cs 0.15 FA 0.85 Pb(I/Br/Cl)3 thin films for optoelectronic applications

The radiation tolerance of mixed-halide perovskites is of considerable interest for next-generation space photovoltaics and nuclear-grade optoelectronics devices operating in harsh radiation environments. In this work, the structural, optical, and electrical evolution of Cs 0.15 FA 0.85 PbI 2.55 Br 0.45 , Cs 0.15 FA 0.85 PbCl 0.45 I 2.55 and Cs 0.15 FA 0.85 PbI 3 thin films subjected to gamma irradiation doses of 0–25 kGy were systematically investigated using X-Ray Diffraction (XRD), UV-Visible spectroscopy, Scanning Electron Microscopy (SEM), and Hall-Effect Measurements. A non-monotonic radiation response was observed, whereby moderate irradiation doses (10-15 kGy) resulted in improved crystallinity and charge transport properties while higher doses (> 20 kGy) induced structural degradation. Quantitative XRD analysis showed that the crystallite size of Cs 0.15 FA 0.85 PbI 2.55 Br 0.45 increased from 51.50 nm to 136.98 nm (approximately 166%) at 15 kGy, accompanied by an approximately 86% reduction in dislocation density and a decrease in microstrain from 0.363% to 0.138%, indicating radiation-induced structural relaxation. At 25 kGy however, the crystallite size decreased to 25.66 nm, while microstrain and dislocation density increased substantially. In contrast, Cs 0.15 FA 0.85 PbCl 0.45 I 2.55 exhibited comparatively smaller variations in crystallite size, microstrain, and dislocation density. It maintained stable p-type conduction throughout the irradiation range, and this is an indication of superior structural and electrical stability. Hall- effect measurements further revealed a n-p-n carrier polarity transition in Cs 0.15 FA 0.85 PbI 2.55 Br 0.45 whereas Cs 0.15 FA 0.85 PbCl 0.45 I 2.55 and Cs 0.15 FA 0.85 PbI 3 retained p-type conduction after irradiation. The combined structural and electrical analyses demonstrate that moderate gamma irradiation (10–15 kGy) promotes defect rearrangement and improved crystalline ordering, whereas higher doses generate lattice defects that degrade charge transport. These findings establish halide engineering as an effective strategy for tailoring radiation tolerance and defect evolution in Cs-doped mixed-halide perovskites, providing important design guidelines for radiation-resistant optoelectronic materials intended for space and nuclear applications.