Size Effects in the Interface Level Alignment of Dye-Sensitized TiO2 Clusters

• Published in: The journal of physical chemistry letters Vol. 5; no. 14; pp. 2395 - 2401
• Main Authors: Marom, Noa, Körzdörfer, Thomas, Ren, Xinguo, Tkatchenko, Alexandre, Chelikowsky, James R
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.07.2014
• Subjects: Molecular Structure, Quantum Chemistry, and General Theory; functional nanostructure; van der Waals; DFT; GW approximation; dispersion interactions; many-body dispersion; electronic structure; quantum size effect; dye-sensitized solar cell; interface engineering
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/jz5008356

The efficiency of dye-sensitized solar cells (DSCs) depends critically on the electronic structure of the interfaces in the active region. We employ recently developed dispersion-inclusive density functional theory (DFT) and GW methods to study the electronic structure of TiO2 clusters sensitized with catechol molecules. We show that the energy level alignment at the dye-TiO2 interface is the result of an intricate interplay of quantum size effects and dynamic screening effects and that it may be manipulated by nanostructuring and functionalizing the TiO2. We demonstrate that the energy difference between the catechol LUMO and the TiO2 LUMO, which is associated with the injection loss in DSCs, may be reduced significantly by reducing the dimensions of nanostructured TiO2 and by functionalizing the TiO2 with wide-gap moieties, which contribute additional screening but do not interact strongly with the frontier orbitals of the TiO2 and the dye. Precise control of the electronic structure may be achieved via “interface engineering” in functional nanostructures.