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

The atomic layer deposition of aluminum oxide on an OH-terminated TiO 2 (101) anatase surface was studied employing density functional theory calculations. The formation of the Al 2 O 3 −TiO 2 interface during the first atomic layer deposition cycle was modeled by studying the dissociative adsorption of an Al(CH 3 ) 3 precursor, followed with a H 2 O-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 Al 2 O 3 ALD cycle is enough to block N3 adsorption on the TiO 2 . Consequently, N3 anchors to the aluminum oxide layer, which increases the dye−TiO 2 distance by ∼2 Å, changes the adsorption site, and weakens the coupling to TiO 2 . All these factors suppress forward electron injection from the dye molecule to the TiO 2 conduction band edge. It is, therefore, questionable whether the aluminum oxide layer can offer improvements to the conversion efficiency in dye-sensitized solar cells.