Effect of binding geometry on interfacial charge transfer in a hybrid dye sensitizer based on a cadmium selenium quantum dot

The separation of photoexcited charge carriers at the quantum dot (QD)-dye interface is determined by the direction of the charge transfer and electronic coupling. We carried out DFT-based studies to analyze the variation of energy level alignment and the associated QD-dye electronic couplings with respect to the surface orientation of Ru505 dye adsorbed on a CdSe QD. Our calculations show that the structures with two carboxylate anchors have the most stable adsorption on the QD surface. These structures have comparable electronic couplings for electron transfer and back electron transfer, and also possess large electronic couplings for hole extraction from the QD, reducing the chance of photoexcited electrons returning to the QD ground state. Using a cyano group to couple a dye to a QD surface stabilizes the dye's occupied orbitals, making hole extraction thermodynamically unfavorable. In addition, these structures show no improvement in their electronic couplings when the cyano group is introduced as anchors. Overall, our computational work advances our understanding of the surface chemistry of a CdSe QD functionalized by Ru505 dye, which may help design QD-based materials for photovoltaic and photocatalytic applications by manipulating the morphologies of QD-dye composites.

Automated summary

By conducting DFT-based studies, this research analyzed the energy level alignment and electronic couplings between Ru505 dye and a CdSe quantum dot, revealing that structures with two carboxylate anchors had the most stable adsorption on the QD surface. These structures showed favorable electronic couplings for electron transfer, back electron transfer, and hole extraction, reducing the likelihood of photoexcited electrons returning to the QD ground state. Introducing a cyano group to couple the dye to the QD surface stabilized the dye's occupied orbitals, making hole extraction thermodynamically unfavorable.