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Halide perovskites have exhibited great research impact for developing innovative materials with novel properties. Here, we report the synthesis of different caesium lead bromide perovskites using different (Cs/Pb) molar ratios and fabrication of their corresponding perovskite/polyvinylidene fluoride (PVDF) composites, as well as study of their structural and UV-photodetection properties. Spin-coated perovskite/PVDF composite thin films revealed strong oriented XRD diffraction peaks along the c -axis direction (00l) with homogeneously distributed perovskite microcrystals in the polymer matrix. The high-Cs containing perovskite/PVDF composite, with Cs/Pb (3/1) molar ratio, demonstrated the highest green emission under UV light and its corresponding UV-photodetector exhibited the highest UV photo-responsivity. These results highlight the importance of structural modulation and additive manufacturing for tailoring the optoelectronic properties of halide perovskites., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Perovskite based on cesium bismuth bromide offers a compelling, non-toxic alternative to lead-containing counterparts in optoelectronic applications. However, its widespread usage is hindered by its wide bandgap. This study investigates a significant bandgap tunability achieved by introducing Fe doping into the inorganic, lead-free, non-toxic, and stable Cs 3 Bi 2 Br 9 perovskite at varying concentrations. The materials were synthesized using a facile method, with the aim of tuning the optoelectronic properties of the perovskite materials. Characterization through techniques such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, energy dispersive spectroscopy (EDS), and UV-vis spectroscopy was conducted to elucidate the transformation mechanism of the doping materials. The substitution process results in a significant change in the bandgap energy, transforming from the pristine Cs 3 Bi 2 Br 9 with a bandgap of 2.54 eV to 1.78 eV upon 70% Fe doping. The addition of 50% Fe in Cs 3 Bi 2 Br 9 leads to the formation of the orthorhombic structure in Cs 2 (Bi,Fe)Br 5 perovskite, while complete Fe alloying at 100% results in the phase formation of CsFeBr 4 perovskite. Our findings on regulation of bandgap energy and crystal structure through B site substitution hold significant promise for applications in optoelectronics., Competing Interests: The authors declare that they have no conflict of interest., (This journal is © The Royal Society of Chemistry.)