Role of Interligand Coupling in Determining the Interfacial Electronic Structure of Colloidal CdS Quantum Dots

• Published in: ACS nano 2016-01, Vol.10 (1)
• Main Authors: Harris, Rachel D., Amin, Victor A., Lau, Bryan, Weiss, Emily A.
• Format: Article
• Language: English
• Subjects: bio-inspired; catalysis (homogeneous); charge transport; dithiocarbamate; exciton delocalization; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ligand−ligand coupling; materials and chemistry by design; mesostructured materials; quantum dot; solar (photovoltaic); synthesis (novel materials); synthesis (self-assembly)
• ISSN: 1936-0851; 1936-086X

Displacement of cadmium oleate (Cd(oleate)2) ligands for the exciton-delocalizing ligand 4-hexylphenyldithiocarbamate (C6-PTC) on the surfaces of CdS quantum dots (QDs) causes a decrease in the band gap (Eg) of the QD of ~100 meV for QDs with a radius of 1.9 nm and ~50 meV for QDs with a radius of 2.5 nm. The primary mechanism of this decrease in band gap, deduced in previous work, is a decrease in the confinement barrier for the excitonic hole. The increase in apparent excitonic radius of the QD that corresponds to this decrease in Eg is denoted ΔR. The dependence of ΔR on the surface coverage of C6-PTC, measured by 1H NMR spectroscopy, appears to be nonlinear. Calculations of the excitonic energy of a CdS QD upon displacement of native insulating ligands with exciton-delocalizing ligands using a 3D spherical potential well model show that this response includes the contributions to ΔR from both isolated, bound C6-PTC ligands and groups of adjacent C6-PTC ligands. Fits to the experimental plots of ΔRvs surface coverage of C6-PTC with a statistical model that includes the probability of formation of clusters of bound C6-PTC on the QD surface allow for the extraction of the height of the confinement barrier presented by a single, isolated C6-PTC molecule to the excitonic hole. Furthermore, this barrier height is less than 0.6 eV for QDs with a radius of 1.9 nm and between 0.6 and 1.2 eV for QDs with a radius of 2.5 nm.