Probing the significance of phenylethyl ammonium doping in Cs₃Bi₂Br₉ halide perovskite nanosheets: a structural and optical perspective

Lead-free halide perovskites have been explored ardently for optoelectronic applications. Organic-inorganic hybrid halide perovskites have shown promise with novel optical properties, bandgap tuning and improved carrier dynamics, while introducing a quantum well structure. Herein, phenylethyl ammonium (PEA), an organic cation, was incorporated into cesium bismuth bromide (CBB) to enhance its multi-quantum well structure and synthesize organic-inorganic hybrid nanosheets of PEA-doped cesium bismuth bromide (PEA:CBB). Optimal doping conditions led to the formation of stable layered PEA:CBB hybrid nanosheets, evidenced by XRD and HRTEM analyses. DFT calculations revealed a minimum-energy structure in which PEA adopts a horizontal alignment between the inorganic slabs of CBB. The incorporation of PEA introduces new electronic states, resulting in extended luminescence tails and altered carrier lifetime. Third-order non-linear optical characterization of pristine and hybrid particles revealed that the multi-quantum well structure and additional trap states induced by PEA increase the two-photon absorption coefficient and reduce the optical limiting threshold of CBB. The present study indicates conceivable relevance of lead-free bismuth-based halide perovskites and their variants in optical limiting applications.