Spectroelectrochemistry of Colloidal CdSe Quantum\nDots

Abstract

Solution-phase\nspectroelectrochemistry was used to study electron\ninjection into colloidal CdSe quantum dots (QDs) with sizes ranging\nfrom 3.4 to 11.1 nm in tetrahydrofuran (THF). The absorbance and photoluminescence\nof the QDs were monitored in response to both charging and discharging\ncycles, and the optical changes were reversible on a timescale of\nminutes. Bleaching of the QD 1S_3/2h1S_e exciton\nstate was used to determine the conduction band energy levels. We\nfound that the negative trion state was stable in THF for hours under\nan applied cathodic potential. Both the degree of bleaching and the\nrecovery of the exciton state depended on the applied potential. Based\non the current and charge measurements, we found that between 10 and\n150 electrons were injected into the QDs, depending on the electrode\npotential and QD size. Most of the electron injection occurred below\nthe band edge and led to quenching of the QD photoluminescence. The\npotential at which injection into QDs occurred depended on the nature\nof the QD ligands.