Ordered Mesoporous Sb-, Nb-, and Ta-Doped SnO₂ Thin Films with Adjustable Doping Levels and High Electrical Conductivity

This paper describes the synthesis and electrical properties of self-organized Sb-, Nb-, and Ta-doped SnO(2) thin films with adjustable doping levels. These transparent conducting oxides (TCOs) were prepared using a poly(ethylene-co-butylene)-b-poly(ethylene oxide) diblock copolymer as well as a novel polyisobutylene-b-poly(ethylene oxide) as organic templates. All samples are highly crystalline and have ordered cubic pore-solid architectures after removal of the polymer template by calcination; however, the electrical conductivity is not identical. The films are characterized by a combination of small- and wide-angle X-ray diffraction/scattering, SEM/TEM imaging, and X-ray photoelectron spectroscopy. Resistivity measurements conducted on the mesoporous frameworks show that the electrical properties strongly depend on both the degree of crystallinity and the elemental makeup. Considerable enhancements of the electrical properties result when the films are doped with antimony and treated in N(2) at elevated temperatures. Such TCO materials show electrical resistivities which are--despite the mesoporous morphology--only 1 order of magnitude higher than reported values for dense Sb-doped SnO(2) films.