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

ABSTRACT Non‐stoichiometric plasmonic semiconductors such as Cu _2‐x S 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‐x S, CsPbBr ₃ 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‐x S to the valence band of CsPbBr ₃ at both excitations, while 400 nm excitation additionally promotes hot‐electron transfer from CsPbBr ₃ to Cu _2‐x S conduction band, leading to efficient charge separation and retarded exciton recombination. These synergistic charge transfer processes establish the Cu _2‐x S‐CsPbBr ₃ heterosystem as a strong candidate for high‐performance optoelectronic devices.