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 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 compared 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 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 Al2O3-induced weakening of electronic coupling between the dye and TiO2 as well as modification of the TiO2 electronic structure.

Dynamics of Back Electron Transfer in Dye-Sensitized Solar Cells Featuring 4-tert-Butyl-Pyridine and Atomic-Layer-Deposited Alumina as Surface Modifiers

“…The effects on J SC and V OC of electrode modification with alumina are similar to those arising from TBP addition, and we assume that the causes are similar. Previous work by Antilla et al 41,42 strongly supports the notion that even small amounts of ALD alumina can lower injection yields sufficiently to substantially degrade short-circuit current densities. 59 From eq 1, an alternative or additional explanation for the modifier-induced decreases in J SC would be increases in J recombination .…”

Free standing TiO2 nanotube array electrodes with an ultra-thin Al2O3 barrier layer and TiCl4 surface modification for highly efficient dye sensitized solar cells

“…[9][10][11][12] But the improvement of DSC power conversion efficiency requires not only to set up direct connection between the light-absorbing and charge-collecting geometry, but also to control the chemistry at the interface between the electrode and electrolyte. Charge recombination reaction of the injected electron with the oxidizing agent of the electrolyte is a deleterious loss pathway even in many planar solar cell devices, 13,14 and such interface recombination generally dominates the performance of high aspect ratio electrodes such as TNT, due to the increased interfacial contact area relative to their projected geometric area for light absorption. Controlling the chemical properties of the surfaces and junctions of such one-dimensional systems as TiO 2 nanotube arrays is therefore especially important.…”

Atomic Layer Deposition for Sensitized Solar Cells: Recent Progress and Prospects

“…Thicker layers impeded the injection too much, reducing short circuit currents. In more fundamental photophysical studies, Korppi‐Tommola and colleagues examined the differences in singlet and triplet injections between a RuN 3 dye and a m‐TiO 2 scaffold with various thicknesses of ALD Al 2 O 3 . These studies found that while singlet injection was systematically suppressed for all Al 2 O 3 ALD coating thicknesses (including a single ALD cycle), triplet injection decreased only for coatings exceeding two Al 2 O 3 ALD cycles.…”