Transparent Conductive Vanadium Oxide-Based Thin Films from Liquid Precursors

New types of transparent conducting materials (TCMs) are being sought due to the increase in demand for their use in next generation electronics and photovoltaics. Methods to improve transparency be inferred by controlling porosity (graded refractive index), or from a change in the crystal structure of some materials that are not inherently transparent at visible frequencies. Transparent materials with tunable optical properties are important in conductive and capacitive displays, tandem solar cells, organic PVs and other devices. In thin film oxide deposition, where non-uniformities and porosity are not ideal, diffusion from glass substrates into oxide thin films during thermal treatment has previously been considered detrimental and was suppressed using diffusion barriers such as thick coatings of SiO₂. In this work, we show how the transparency and conductivity of a dip-coated thin film of vanadium oxide can be markedly improved by substrate diffusion during thermal treatment, resulting in a completely transparent thin film of vanadium oxide-based material with an order of magnitude increase in electrical conductivity. The phase change and stoichiometry variation during thermal annealing of the vanadium oxide dip-coated from liquid precursors is elucidated using X-Ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Angle-resolved transmission spectra correlated the transparency to the changes in optical properties of the thin films and electron microscopy confirms no formal structural change contributes to the change in transparency. Hall probe measurements demonstrate improved conductivity with transparency due to diffusion of cations from the substrate into the host material lattice. 

References:

1. C. M. Eliason and M. D. Shawkey, Opt. Express, 22, A642 (2014).
2. C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotechology, 4, 239 (2009).
3. J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007).
4. C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013).
5. C. Glynn, D. Creedon, H. Geaney, J. O'Connell, J. D. Holmes and C. O'Dwyer, ACS Appl. Mater. Interfaces, 6, 2031 (2014).
6. K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T. Leedham, J. Rickard and H. Sirringhaus, Nature Materials, 10, 45 (2011).
7. J. Mannhart and D. G. Schlom, Science, 327, 1607 (2010).
8. F. Nicholas, M. P. Sean, W. H. Mark and S. S. N. Bharadwaja, Journal of Physics D: Applied Physics, 42, 055408 (2009).
9. T. Manning, I. Parkin, Polyhedron, 23, 3087 (2004).