Investigation of Photoinduced Charge Transfer between Heavy metal-free Semiconductor Quantum Dots and ZnO Nanorods

Semiconductor nanoparticles and their assemblies are considered as building blocks of next generation nanoscale electronic devices. In particular, for solar cell applications, the photoexcited charge carriers need to be transferred efficiently to the charge transport layer. However, the major limitations of such charge transfer process are the radiative or non-radiative recombination of photoexcited charge carriers and the charge trapping at localized electronic states. The rate of charge transfer depends on the electronic coupling of excited donor and acceptor states, which can be controlled by the spatial extension charge carrier?s wave function into the donor surface. In this proposal, we aim to investigate the photoinduced charge transfer from CuInS2/ZnS (CIS) and InP/ZnS (InP) core/shell QDs to ZnO nanorods. The selection of CIS and InP QDs is based on two aspects; first they have different electronic confinement potentials. For CIS QDs, the confinement potential is ca. 664 meV where as that of InP QD is ca. 1194 meV. Hence the spatial extension of the charge carrier wave function is expected to be larger for CIS QDs. Second, CIS QDs is having relatively long PL lifetime (ca. 290 ns) as compared to InP QDs (ca. 37 ns). Consequently, the rate of PCT is expected to be higher for CIS QDs on ZnO nanorods. We are going to use ZnO nanorods as acceptor because of its relatively larger surface area and better charge transport properties. The larger surface area may help us to increase the donor loading, hence increasing the light absorption. The charge transport is expected to be better in nanorods as compared to nanoparticles due to less charge trapping at the interface between donor and acceptor species. The main objective of this project is to study the charge transfer behavior locally using a wide field optical microscope. This way we can reveal the heterogeneity of transfer rates on the sample surface. Therefore, we need to build an optical microscope coupled with a pulsed laser so that the PL decay can be measured on different locations on the sample surface.