Enhanced Carrier Densities in Indium Tin Oxide Films Covered with Nanoparticles of Fluorine-Doped Tin Oxide for Transparent Conducting Electrodes

摘要

The carrier density and Hall mobility of indium tin oxide (ITO) films uniformly deposited with single layers of monodispersive nanoparticles of fluorine-doped tin oxide (FTO) show intriguing variations as functions of the average size of FTO particles (D_(av)). For D_(av)s smaller than about 10 nm, the bilayer has conduction-electron densities lower than bare ITO films, accompanied by increased Hall mobilities. Surprisingly, for D_(av)s of a few tens of nanometers, the carrier density in the bilayer is higher by at least 30% than that of bare ITO films. A classical double-Schottky band model of an n-n isotype heterojunction can account for these behaviors. This model assumes high-density local states at the ITO-film/FTO-nanoparticle interface, which trap conduction electrons, while FTO nanoparticles act as electron injectors. It is pointed out that the ability to control the optoelectronic properties simply by optimizing the film structure is useful in applications to practical transparent conducting electrodes.