Atomic Layer Deposition of Aluminum Oxide on TiO2 and Its Impact on N3 Dye Adsorption from First Principles

Abstract

The atomic layer deposition of aluminum oxide on an OH-terminated TiO2(101) anatase surface was studied employing density functional theory calculations. The formation of the Al2O3−TiO2 interface during the first atomic layer deposition cycle was modeled by studying the dissociative adsorption of an Al(CH3)3 precursor, followed with a H2O-pulse reaction step that changes the surface termination. Calculations provide evidence for the formation of a discontinuous, atomically rough aluminum oxide layer after the first cycle. To explore the role of the aluminum oxide layer on adsorption of a ruthenium-based N3 dye molecule, various adsorption geometries were investigated. Calculations show that even one Al2O3 ALD cycle is enough to block N3 adsorption on the TiO2. Consequently, N3 anchors to the aluminum oxide layer, which increases the dye−TiO2 distance by ∼2 Å, changes the adsorption site, and weakens the coupling to TiO2. All these factors suppress forward electron injection from the dye molecule to the TiO2 conduction band edge. It is, therefore, questionable whether the aluminum oxide layer can offer improvements to the conversion efficiency in dye-sensitized solar cells.