High efficiency quasi-solid dye sensitized solar cells consisting of organic-inorganic hybrid ionic paths

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Solidification of dye sensitized solar cells (DSC) is one of the most crucial research items. Solidification generally decreases ionic diffusion and lower the solar cell efficiency. Because of this, quasi-solidification is one of the most promising candidates for the solidification. However, quasi-solidified DSCs reported so far are soft gel and the solidification ratio (solid part/all carrier layer) was less than 10-20% because the high solidification ratio lowers the efficiency. Our purpose is to propose high efficiency quasi-solid DSCs with high solid content more than 50% (so-call high solid type quasi-solid DSCs). In this research program, we proposes hybrid quasi-solid DSCs consisting of a high carrier density layer and a low carrier density layer. The former fills the bulk layer between a TiO_2 layer and a counter electrode and the latter fills the nano-pores in TiO_2 layers. The former brings about high conductivities in the solid state layer (bulk layer) and the latter prevents back electron transfer from the TiO_2 to carrier layer. The proposal was realized by three cell structures, namely, surface modified porous Al_2O_3/ionic liquid type electrolyte, surface modified nano-oxide materials/ionic liquid type electrolyte, and a composite carrier transport layer consisting of porous Al_2O_3 membrane/conductive polymer/ionic liquid type electrolyte. In all cases, carriers were concentrated in the surface-modified nano-structured materials, resulting in making high carrier concentration areas. The photovoltaic properties of the high solid type solar cells (solidification ratio/more than 50%) were almost the same as or higher than those of the cells before the solidification. It was proved that the hybrid solar cells consisting of two carrier concentration layers are effective structure having high photovoltaic properties and the idea has generality for fabricating high efficiency solid solar cells.