Surface Fluorination for Controlling the PbS Quantum Dot Bandgap and Band Offset

• Published in: Chemistry of materials Vol. 30; no. 15; pp. 4943 - 4948
• Main Authors: Xia, Pan, Liang, Zhiming, Mahboub, Melika, van Baren, Jeremiah, Lui, Chun Hung, Jiao, Jieying, Graham, Kenneth R, Tang, Ming Lee
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.08.2018
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.8b00930

Fully fluorinated perfluorocarbon ligands are shown to modify the energetics and dielectric environment of quantum dots (QDs), resulting in a large hypsochromic shift in the optical gap. The original oleic acid (OA) ligands on PbS QDs can be completely replaced with thiolate and carboxylate-based perfluorocarbons, e.g., -SCF3 and CF3(CF2)14COOH (pFA), respectively. Ultraviolet photoelectron spectroscopy indicates that the work function varies by >1.3 eV depending on the electronegativity of the surface ligand, while cyclic voltammetry shows that an OA:pFA ratio of ∼2:1 increases the oxidation potential by 0.18 eV in solution. The diminished reduction potential of the conduction band is confirmed by photoinduced electron transfer experiments. The short thiolate ligands, -SCF3 and -SCH3, enhance the electron-donating ability of PbS QDs up to 7-fold because of an increase in the permeability of the ligand shell. This work shows that electron-withdrawing halogens like fluorine and chlorine can control the bandgap and band offsets of nanocrystals for the future design and optimization of functional organic/inorganic hybrid nanostructures.