Spectral and dynamical properties of multiexcitons in semiconductor nanorods

Understanding multiple charge carrier relaxation dynamics in semiconductor nanocrystals is crucial for utilizing their full potential, as it allows to guide the design of optimized structures. Multiple excitons dynamics often are characterized via the observation of additional fast exponential kinetics at band edge in transient absorption spectroscopy data with increasing excitation intensities. However, these investigations are complicated by the formation of surface localized excitons which also introduce additional fast decay components which could falsely be interpreted as multiexciton kinetics in semiconductor nanocrystals. Another challenge presents the generation of a distribution of species in dependence of the excitation intensity not only including single and double excited systems, but even higher-order multiple excitons. In this study we used intensity dependent transient absorption spectroscopy with broadband probing spanning the whole visible range to identify characteristic spectroscopic signatures for the presence of multiple excitons of varying order in seeded and non-seeded CdS nanorods. Applying an MCMC sampling approach for global target analysis enables us to determine contributions of multiple exciton decay via Auger recombination and population of surface exciton states to the observed transient dynamics. The influence of surface chemistry, i.e., the nature of the surface ligands on multiexciton dynamics of nanorods is studied.