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, we have incorporated phenylethyl ammonium (PEA), an organic cation in cesium bismuth bromide (CBB) to enhance the multi-quantum well structure of CBB and form organic-inorganic hybrid nanosheets of PEA doped cesium bismuth bromide (CBB). The optimum addition of dopant led to the formation of stable layered PEA: CBB hybrid nanosheets, evidenced from XRD and HRTEM analysis.The possible stable structure of the hybrid nanosheets was elucidated via DFT calculations. This revealed a minimum energy structure with PEA coordinated in a horizontal configuration in-between inorganic slabs of CBB. PEA incorporation leads to the formation of new electronic states instigating longer tails in luminescence spectrum and variation in carrier lifetime. Third order non-linear optical characterization of the pure and hybrid particles revealed the multi-quantum-well structure and additional trap states brought about by PEA incorporation increases the two-photon absorption coefficient and decreases the optical limiting threshold of CBB. The present study indicates conceivable relevance of lead-free bismuth based halide perovskites and its variants in optical limiting applications.