Effect of Nanocrystal Shape on Charge Injection and Transport in CdSe Nanocrystalline Films

Understanding of charge transport (CT) in assemblies of quantum confined semiconductor nanocrystals (NCs) is an important prerequisite for their effective exploitation in optoelectronic applications. Here we use spectro-electrochemistry (SEC) to investigate CT in thin films comprising symmetric CdSe quantum dots (QDs) and asymmetric nanorods (NRs) with similar diameters and NR aspect ratios from 1.8 to 6.7. We find that the efficiency and dynamics of CT depends strongly on size and shape of the NCs as well as on the molecular linkers used in the preparation of the films. For films prepared under similar conditions CT is more efficient in NR films than in QD films. This is attributed to the asymmetry of the NRs resulting in formation of large channels within the film, which allow an efficient diffusion of charge-balancing counterions of the electrolyte. When comparing the NR films, the CT is more efficient in films prepared from thicker NRs and NRs with higher aspect ratios.