Selective positioning of organic dyes in a mesoporous inorganic oxide film

Although sequential adsorption of dyes in a single TiO₂ electrode is ideal to extend the range of light absorption in dye-sensitized solar cells, high-temperature processing has so far limited its application. We report a method for selective positioning of organic dye molecules with different absorption ranges in a mesoporous TiO₂ film by mimicking the concept of the stationary phase and the mobile phase in column chromatography, where polystyrene-filled mesoporous TiO₂ film is explored for use as a stationary phase and a Brønsted-base-containing polymer solution is developed for use as a mobile phase for selective desorption of the adsorbed dye. By controlling the desorption and adsorption depth, yellow, red and green dyes were vertically aligned within a TiO₂ film, which is confirmed by an electron probe micro-analyser. The external quantum efficiency (EQE) spectrum from a solar cell with three selectively positioned dyes reveals the EQE characteristics of each single-dye cell.