Plasmon‐Exciton Interaction Induced Efficient Charge Separation in Cu _2‐x S‐CsPbBr ₃ Heterostructure

Non-stoichiometric plasmonic semiconductors such as Cu_2-xS have emerged as promising materials for energy conversion applications owing to their tunable band gaps, cost-effectiveness, and ability to harvest near infrared (NIR) energy. Integrating these plasmonic semiconductors with lead halide perovskites in heterostructures enables strong plasmon-exciton coupling, resulting in enhanced light absorption and efficient interfacial charge transfer. This work presents a synthesis and investigation of the spectroscopic behaviour of non-stoichiometric Cu_2-xS, CsPbBr₃ nanocrystals (NCs) and their heterostructure. Femtosecond transient absorption (TA) measurements are performed at two different excitations (400 and 800 nm) to develop a fundamental understanding of the hot carrier dynamics and their extraction in the heterostructure system. The TA results confirm plasmon-induced hot-hole transfer from Cu_2-xS to the valence band of CsPbBr₃ at both excitations, while 400 nm excitation additionally promotes hot-electron transfer from CsPbBr₃ to Cu_2-xS conduction band, leading to efficient charge separation and retarded exciton recombination. These synergistic charge transfer processes establish the Cu_2-xS-CsPbBr₃ heterosystem as a strong candidate for high-performance optoelectronic devices.