Optimizing Electron Delocalization in CdSe-CdS Heteronanostructures: Insights from Single-Particle Photoluminescence Studies

Developing semiconductor systems for light energy harvesting and photocatalysis necessitates the stabilization of photogenerated charge carriers. Achieving charge carrier separation in heteronanostructures involves the band engineering of two distinct semiconductors and extending the delocalization length of charge carriers. The radiative lifetime of the neutral exciton measures the extent of the charge delocalization. Nevertheless, the contributions of trap-assisted nonradiative decay channels significantly influence the overall radiative lifetime in ensemble measurements; hence, it is difficult to quantify charge carrier delocalization. Herein the radiative recombination dynamics of neutral exciton in heteronanostructures, comprising a CdSe quantum dot as core and a CdS shell with tadpole morphology (CdSe-CdS) are investigated through time-resolved single-particle spectroscopy. The CdSe-CdS system exhibits quasi-type II characteristics, resulting in the localization of a hole within the CdSe core, while the electron is predominantly delocalized between the CdSe core and the CdS shell. The neutral exciton recombination lifetime is determined by analyzing the high-intensity component in the photoluminescence intensity-time traces by varying the core size of the CdSe quantum dots and increasing the length of the CdS shell. These studies elucidate that electron delocalization is more efficient in CdSe-CdS heteronanostructures with a smaller CdSe core diameter and an extended CdS shell length.