Formation of a crystalline nanotube-nanoparticle hybrid by post water-treatment of a thin amorphous TiO2 layer on a TiO2 nanotube array as an efficient photoanode in dye-sensitized solar cells

An atomic layer deposited, conformal thin layer (similar to 15 nm) of amorphous TiO2 on a primary TiO2 NT array is effectively converted into partly crystalline nanoparticles on the inside walls of TiO2 nanotubes by water mediated dissolution-precipitation phenomena without disturbing the original state of the TNTAs. This method helps to achieve the exclusive conversion of the secondary shell of amorphous TiO2 layer coated by ALD into nanoparticles and the preservation of original crystalline nanotube (core) properties such as mechanical stability and the charge transport properties. As a consequence, the resultant core-shell type nanotube-nanoparticle composite showed higher photoanode performance (25% increment in efficiency) than conventional untreated TiO2 NT array photoanode.