Quasi-solid dye sensitized solar cell with straight ion paths - Proposal of hybrid electrolytes for ionic liquid-type electrolytes

Quasi-solid dye sensitized solar cells (QDSC) with straight ion paths are reported. The cell consists of anodic oxidation Al2O3 films. Ionic liquid-type electrolyte is filled in the straight nanopores and they are sandwiched between a counter electrode and a TiO2 electrode. Even when electrochemically inactive Al2O3 wall occupies 50% of the electrolyte layer, the I-3(-) diffusion coefficient and solar cell performance are the same as those without the Al2O3 layers. This contrasts the results of cells filled with the mixture of Al2O3 nanoparticles and ionic liquid type electrolytes, where random ion paths are expected. In addition, when the inner wall of anodic oxidation Al2O3 films is chemically modified with long alkyl groups bearing methylimidazolium moieties, the increase in photovoltaic performance is observed. This is explained by the existence of ion paths along aligned methylimidazolium moieties in the surface-modified Al2O3 films, where I-2(I-3(-)) species are concentrated. The swift apparent I-3(-) diffusion coefficient is explained by Grotthuss mechanism. Because the I-2 species are concentrated in the straight pore of Al2O3 layers, the concentration of I-2(I-3(-)) species in TiO2 layers is reduced relatively. This increases light penetration depth at around 400 nm in the porous TiO2 layer and improves incident photon-to-current efficiency at around 400 nm. The hybrid electrolyte systems containing both of concentrated I-2(I-3(-)) in a porous Al2O3 layer and low concentration portions in nanopores in TiO2 are proposed to increase ionic liquid-type QDSC. (c) 2006 The Electrochemical Society.