Effect of 2D MXene-to-nanoparticle ratio on the electronic structure of Ti₃C₂ MXene-CsPbBr₃ nanocomposites

MXene-CsPbBr₃ nanocomposites have garnered significant interest for next-generation optoelectronics, combining tunable quantum effects with exceptional charge transport characteristics. Realizing optimal functionality, however, necessitates precise control over the 2D MXene-to-nanoparticle ratio. Herein, we systematically elucidate how this ratio governs the electronic structure and charge dynamics in Ti₃C₂ MXene-CsPbBr₃ nanocomposites using scanning tunnelling spectroscopy (STS), electrostatic force microscopy (EFM), and Kelvin probe force microscopy (KPFM). STS reveals distinct density of states for isolated CsPbBr₃ nanoparticles chemically bonded to MXene compared to aggregated counterparts. Schottky junctions at well-defined interfaces promote charge separation, whereas nanoparticle aggregation induces defect-mediated states, narrowing the CsPbBr₃ bandgap and opening a gap in Ti₃C₂. Correlated EFM-KPFM analyses further demonstrate that isolated nanoparticles yield uniform electrostatics and homogeneous surface potentials, while aggregates generate localized fields and patchy work-function distributions. These results demonstrate that nanoscale electrostatics and interfacial coupling critically dictate carrier dynamics, enabling the rational design of tunable optoelectronic device architectures.