The use of colloidal nanocrystals as part of artificial photosynthetic systems has recently gained significant attention, owing to their strong light absorption and highly reproducible, tunable electronic and optical properties. The complete photocatalytic conversion of water to its components is yet to be achieved in a practically suitable and commercially viable manner. To complete this challenging task, we are required to fully understand the mechanistic aspects of the underlying light-driven processes involving not just single charge carriers but also multiple charge carriers in detail. This review focuses on recent progress in understanding charge carrier dynamics in semiconductor nanocrystals and the influence of various parameters such as dimension, composition, and cocatalysts. Transient absorption spectroscopic studies involving single and multiple charge carriers, and the challenges associated with the need for accumulation of multiple charge carriers to drive the targeted chemical reactions, are discussed.

Polymer–semiconductor hybrid materials or composites have been investigated with respect to their microstructure, optical, photoconductive, and ferroelectric properties. For this purpose, either CdSe quantum dots or (Cd:Zn)S microparticles were dispersed in poly(vinylidenefluoride-trifluoroethylene) solution and hot pressed to films. In both material systems, the electrical conductivity and the polarization behavior could be controlled by the intensity of the optical excitation. The simultaneous high optical transparency of the CdSe quantum-dot-based hybrid materials makes them particularly interesting for applications in the field of flexible, high-resolution sensors.

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.