Thickness-Dependent Charge Carrier Dynamics in CdSe/ZnSe/CdS Core/Barrier/Shell Nanoheterostructures

Insight into morphology dependent charge carrier dynamics in ZnSe-CdS nanoheterostructures

Semiconductor nanoheterostructures (NHSs) are being increasingly used for the photocatalytic conversion of solar energy in which photo-induced charge separation is an essential step and hence it is necessary to understand the effect of various factors such as size, shape, and composition on the charge transfer dynamics. Ultrafast transient absorption spectroscopy is used to investigate the nature and dynamics of photo-induced charge transfer processes in ZnSe-CdS NHSs of different morphologies such as nanospheres (NSs), nanorods (NRs), and nanoplates (NPs). It demonstrates the fast separation of charge carriers and localization of both charges in adjacent semiconductors, resulting in the formation of a charge-separated (CS) state. The lifetime of the charge-separated state follows the order of NSs < NPs < NRs, emphasizing the effect of morphology on the enhancement of photo-induced charge separation and suppression of backward recombination. The separated charge carriers have been utilized in visible light driven hydrogen production and the hydrogen generation activity follows the same order as that for the lifetime of the CS state, underlining the role of charge separation efficiency. Therefore, the variation of the morphology of NHSs plays a significant role in their charge carrier dynamics and hence the photocatalytic hydrogen production activity.

Impact of Bifunctional Ligands on Charge Transfer Kinetics in CsPbBr3-CdSe/CdS/ZnS Nanohybrids

Mixed dimensional nanohybrids (MDNHs) between zero-dimensional (0D) perovskites and two-dimensional (2D) II-VI semiconductors hold great potential for photonic device applications. An in-depth study to understand the shuttling of charge carriers is carried out utilizing bifunctional ligands such as 4-aminothiophenol (4-ATP), p-aminobenzoic acid, and 6-amino-2-naphthoic acid in the synthesis of MDNHs of CsPbBr₃ nanocrystals (NCs) and CdSe/CdS/ZnS core/shell/shell (CSS) nanoplatelets (NPLs). These MDNHs form donor-bridge-acceptor systems, where the electronic interaction is greatly influenced by the nature of ligands. The smaller size and stronger binding affinity of 4-ATP to CSS NPLs lead to a faster rate of charge transfer as compared to other linkers. Electronic structure calculations under the framework of density functional theory (DFT) confirms that in 4-ATP capped CSS NPLs, stronger electronic overlap occurs between CSS NPLs and 4-ATP at the valence band maxima (VBM). Furthermore, Poisson distribution modeling proposes that in 4-ATP linked MDNHs, the number of CSS NPLs around CsPbBr₃ NCs is highest.

Efficient Charge Extraction from CdSe/ZnSe Dots-on-Plates Nanoheterostructures

An efficient and a selective charge extraction from a new type of heterostructured material is demonstrated: the quasi-type-II structure formed upon deposition of ZnSe quantum dots on CdSe nanoplatelets, termed as CdSe/ZnSe dots-on-plates (DoPs) heterostructures. Insights into the charge extraction mechanism are gained from the present studies. Quenching experiments on nanoplatelets (NPLs) and DoPs using electron (benzoquinone) and hole (pyridine) quenchers show the possibility of electron extraction leaving behind the hole in the nanostructures. These outcomes indicate more labile electron extraction in comparison with the hole from these DoP structures vis-à-vis the plate only nanostructures, thereby enabling materials for devices requiring only one type of charges. In CdSe NPLs, the excitons are short-lived making them difficult for various applications involving charge separation. The CdSe/ZnSe DoPs could be alternate candidates for overcoming the difficulties involved with NPLs.