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Uchida H.,Sophia University | Patel M.N.,Institute of Chemical Technology | May R.A.,Texas Materials Institute | Gupta G.,Institute of Chemical Technology | And 2 more authors.
Thin Solid Films | Year: 2010

Highly ordered mesoporous titanium dioxide (titania, TiO2) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO2 buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO2 buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO2-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO2 buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO2 film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO2 (~ 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications. © 2009 Elsevier B.V. All rights reserved.

Hahn B.P.,Texas Materials Institute | Stevenson K.J.,Texas Materials Institute
Journal of Electroanalytical Chemistry | Year: 2010

Molybdenum-selenium oxides were electrochemically deposited onto indium-tin oxide (ITO) coated glass substrates from aqueous solutions containing molybdate (MoVI O4 2 -), selenate (SeIV O3 2 -), and dimeric and tetrameric peroxo-polymolybdate (i.e., [Mo2O3(O2)4(H2O)2]2-, [Mo4O9(O2)4]2-) anions. Electrodeposition mechanisms were elucidated using chronocoulometry, cyclic voltammetry, spectroelectrochemistry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical quartz crystal nanogravimetry (EQCN). At relatively positive deposition potentials from -0.1 V to -0.4 V (versus Ag/AgCl) a substoichiometric molybdenum oxide phase, Mo3O8, co-deposits with an insulating phase of Se0. At more negative potentials, mixed molybdenum-selenium oxides (MoxSe1-xOy, 0 < x < 0.4) are deposited. Competing side reactions involving hydrogen and hydrogen selenide influence the structure, composition, and morphology of the mixed molybdenum-selenium oxide deposits. © 2009 Elsevier B.V. All rights reserved.

Harvey T.B.,Center for Nano and Molecular Science and Technology | Harvey T.B.,Texas Materials Institute | Mori I.,University of Tokyo | Stolle C.J.,Center for Nano and Molecular Science and Technology | And 19 more authors.
ACS Applied Materials and Interfaces | Year: 2013

The power conversion efficiency of photovoltaic devices made with ink-deposited Cu(InxGa1-x)Se2 (CIGS) nanocrystal layers can be enhanced by sintering the nanocrystals with a high temperature selenization process. This process, however, can be challenging to control. Here, we report that ink deposition followed by annealing under inert gas and then selenization can provide better control over CIGS nanocrystal sintering and yield generally improved device efficiency. Annealing under argon at 525 C removes organic ligands and diffuses sodium from the underlying soda lime glass into the Mo back contact to improve the rate and quality of nanocrystal sintering during selenization at 500 C. Shorter selenization time alleviates excessive MoSe2 formation at the Mo back contact that leads to film delamination, which in turn enables multiple cycles of nanocrystal deposition and selenization to create thicker, more uniform absorber films. Devices with power conversion efficiency greater than 7% are fabricated using the multiple step nanocrystal deposition and sintering process. © 2013 American Chemical Society.

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