Synthesis and characterization of polypyrrole encapsulated formamidinium lead bromide crystals for fluorescence memory recovery

Impressive optical properties of organic–inorganic lead halide perovskite crystals make them suitable for optoelectronic devices. However, these crystals are unstable in water and other polar solvents and quickly lose their fluorescence which cannot be recovered by the addition of non-polar solvents. Fluorescence recovery is absolute necessity for long-term stability of perovskite in optoelectronic devices. Till date, there is no report showing mechanism of fluorescence recovery of organic–inorganic lead halide perovskite crystals. Here, we have reported the synthesis of FAPbBr₃/polypyrrole (PPy) composites (FA = Formamidinium) for shedding light on the mechanism of fluorescence recovery in presence of N,N Dimethyl formamide or DMF. We have synthesized FAPbBr₃ crystals at room temperature and tuned their band gap from green to blue by varying the amount of surfactant. Similar study was repeated with FAPbBr₃/PPy composites, synthesized through in situ polymerization. Encapsulation was found to improve the emission quality and purity of the colour and successfully restored the fluorescence memory which was lost in presence of DMF. The recovery was attributed to resurfacing of PPy in presence of toluene which brought the building blocks of FAPbBr₃ crystals back to the co-crystallization domain. In brief, this fundamental finding could pave the future way for achieving long-term stability of perovskite crystals in optoelectronic devices.