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

Subnanometer-thick Al2O3 barrier layers on nanocrystalline TiO2 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 compare to e.g., sol-gel techniques. In this letter we present results on the effect of Al2O3 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 discountinuous layer with nominal thickness of 1 angstrom. 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 Al2O3-induced weakening of electronic coupling between the dye and TiO2 as well as modification of the TiO2 electronic structure.