Investigation of Quantum Confinement in Lead Sulfide Quantum Dots, through Cyclic Voltammetry

Due to the large Bohr radius (18nm) and formation of the multi-excitons per photon, lead sulfide quantum dots (Q-PbS) have been viewed as an important material in the light harvesting devices. A performance of these devices however is greatly relying on the formation of hetero-junctions for which the knowledge of relative band positions of the components is desirable. These values are normally estimated by ultra-violate photoelectron spectroscopy (UV-PES) and scanning tunneling spectroscopy (STS). In both the cases one need special sample preparation protocols and involved instrumentation. Here, we demonstrated that these parameters can readily be gauged by electrochemical technique such as Cyclic Voltammetry.  For that, Q-PbS in the size-range 3-5nm  have been prepared by solvo-thermal method and cyclic voltammograms were recorded on their dispersions in dichloromethane.  Distinct cathodic and anodic peaks observed in CV have been co-related to the electron transfer, mediated through the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the Q-dots, respectively. Systematic correlation was observed between the size of Q-dots and the position of HOMO and LUMO which is attributed to the quantum confinement of the charge pairs. The results were found to be matched very well with the one reported with PES in air.