Spectroelectrochemical Characterization of Cadmium Selenide Quantum Dots

Abstract

Understanding and controlling the energetic structures of quantum dots (QDs) isimportant in designing high-efficiency QD-based optoelectronic devices. Spectroelectrochemistry (spec-echem) is a versatile technique to study the optical properties of materials. In this thesis, development of a reproducible and valid procedure for spectroelectrochemically determining the size-dependent band structure of CdSe QDs is described. An attenuated total reflectance (ATR) configuration was used to detect weak absorption changes of submonolayer QD films. Variables that can potentially impact the band structure of QDs, including electrolyte concentration and surface composition of QDs, were identified. These variables caused significant differences between the results reported herein and literature values. We observed that decreasing the cation concentration in the electrolyte shifts the band edge energies closer to the vacuum level, presumably because of the decreased proximity of cations to QDs. Depositing QDs on a phosphonic acid-modified ITO substrate reduces the size of QDs due to the displacement of Cd atoms. The size reduction increases the effect of quantum confinement and increases the bandgap. The surface composition may be changed from Cd-rich to Se-rich during the deposition, potentially shifting the band edge energies. Overall, these findings helped refine procedures for spectroelectrochemical characterization of nanocrystal films and optimize the design of future QD-based optoelectronic devices.