Suppression of Forward Electron Injection from Ru(dcbpy)₂(NCS)₂ to Nanocrystalline TiO₂ Film As a Result of an Interfacial Al₂O₃ Barrier Layer Prepared with Atomic Layer Deposition

Abstract

Subnanometer-thick Al 2 O 3 barrier layers on nanocrystalline TiO 2 film were prepared with atomic layer deposition (ALD). The method allowed variation of barrier thicknesses at atomic resolution also deep in nanoporous structures, which makes it a superior method as compared to, e.g., sol−gel techniques. In this letter we present results on the effect of Al 2 O 3 barriers of various thicknesses on forward electron injection in dye-sensitized solar cells. A decrease in the amplitude of the oxidized Ru(dcbpy) 2 (NCS) 2 dye absorption signal due to singlet injection was observed already after one deposition cycle that produces a discontinuous layer with nominal thickness of 1 Å. More than two layer coatings also slowed down the triplet injection. The findings indicate suppression of total electron injection, which is probably due to the Al 2 O 3 -induced weakening of electronic coupling between the dye and TiO 2 as well as modification of the TiO 2 electronic structure.