Subcategory: Materials Science
Kevin Dominguez - The City College of New York
Co-Author(s): 1. Megan Webster 2. Ilona Kretzschmar
Semiconducting nanocrystals, specifically, quantum dots (QD), have size-tunable band gaps. QDs are size-tunable and can be bound with other compounds to alter their optical and semiconducting properties. Because of this, they have great potential in the field of light-harvesting devices, like light emitting diodes (LED) and fluorophores. In this project, we will be working on growing a ZnS shell on CdSe QDs to study this system and evaluate its applicability in QD-sensitized solar cells (QDSSC). Our CdSe QDs are approximately 2 nm in diameter and emit white light, which is comprised of all the wavelengths in the visible light spectrum. Two theories to explain this are; 1) surface defects in the form of surface traps and 2) high disorder on the surface which leads to structural changes. In order to expand on these theories and to study the surface, ZnS shell growth will be implemented on CdSe QDs. Zinc diethyldithiocarbamate will be used as the precursor for making the ZnS shell material. Capping CdSe QDs with ZnS will create a type-I QD, which will establish charge separation between the shell and core of the crystal. This will help confine charge carriers to the core, which helps facilitate an inert environment where the disorder of the CdSe can be examined. This will allow us to characterize the system and to determine its applicability in QDSSCs. In terms of QDSSC application, we can increase or decrease the thickness of the shell to change the emission and absorption ranges of the QD . Coupled with this, the charge separation that comes with the type-I design can increase the lifetime of excited electrons. The electron excitation and lifetime can be tested with time-correlated single photon counting (TCSPC). The structure and composition of the QDs will be measured and tested with transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). This design will allow us to evaluate how shell growth affects charge transfer within this capped CdSe quantum dot and whether it can absorb photons unabated by the presence of the shell.Not Submitted
Funder Acknowledgement(s): I acknowledge Professor Ilona Kretzschmar as the funder of this project.
Faculty Advisor: Ilona Kretzschmar, firstname.lastname@example.org
Role: I have helped with making and cleaning the solvent, n-oleyl morpholine (NOM), that is used to make the cadmium selenide (CdSe) quantum dots (QD). I have extensively characterized NOM by running multiple gas chromatography-mass spectrometry (GCMS) tests on NOM samples. I have made a zinc sulfide (ZnS) stock solution to synthesize CdSe-ZnS core/shell QDs. I have made solar cells that consist of fluorine tin oxide (FTO) glass, platinum deposited electrodes, and zinc oxide (ZnO) semiconducting material. I have tested these solar cells by using a dye-sensitized solar cell (DSSC) setup and linear sweep voltammetry tests.