Exceeding 100 µs Charge Carrier Separation in Perovskite Mediated by Rhodamine 6G

Halide perovskite colloidal nanocrystals (NCs) have enabled considerable progress in light conversion applications. However, the presence of unavoidable defect states and phase transition effects can accelerate undesirable rapid charge recombination of the photogenerated charge carriers. To address this issue, chromophores with an anchoring moiety are often used to modify the surface of the NCs, promoting prolonged charge separation through electron or energy transfer processes for optoelectronic applications. Here, steady-state and time-resolved spectroscopy methods are combined with density functional theory (DFT) calculations to explore and decipher the excited-state interaction in colloidal CsPbX₃ (X = Br, I) NCs with a rhodamine 6G (Rh6G) hybrid assembly. The results show that Rh6G dimerizes even at low concentrations, as evidenced by DFT calculations. The binding of Rh6G on the NC surface is confirmed by FTIR and NMR spectroscopy techniques. In addition, transient absorption spectroscopy reveals directional sub-ps electron transfer from Rh6G to CsPbI₃ NCs, whereas energy transfer occurs from CsPbBr₃ to Rh6G, which ultimately recombines in the µs time regime. The findings highlight the simplest and most practical approaches for studying and tailoring the excited-state interaction in colloidal perovskite NCs and chromophore assembly.