Thin Films Made from Colloidal Antimony Tin Oxide Nanoparticles for Transparent Conductive Applications
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Thin Films Made from Colloidal Antimony Tin Oxide Nanoparticles for Transparent Conductive Applications Abigail Halim and Rosario A. Gerhardt School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, GA 30332-0245, U.S.A. ABSTRACT Commercially available antimony tin oxide (ATO) nanoparticles were dispersed in water using tetramethylammonium hydroxide (TMAH) as a dispersing agent and deposited onto glass substrates by spin coating. Films of one to five layers were made. These thin films were characterized using impedance spectroscopy and ultraviolet-visible spectroscopy to obtain their sheet resistances and optical transmittance, respectively. The films displayed sheet resistances around 105-106 kȍ/ and optical transmittance in the near infrared to near ultraviolet range above 95%. Films were then made using a higher concentration ATO solution and found to achieve sheet resistances on the order of 102 kȍ/ but had decreased transmittance as low as 65% at some wavelengths. Impedance measurements, along with optical micrographs, were taken at different locations on the films. These experiments demonstrated that films of more than one layer showed greater uniformity. Additional sets of films were also produced with varying substrate preparation and dispersion deposition parameters. Aside from dispersion concentration, high humidity during film measurement was found to be the most crucial parameter for achieving low sheet resistances. INTRODUCTION Transparent conducting oxides (TCOs) are thin films of metal oxides that exhibit both optical transparency and electrical conductivity [1]. For these reasons, they have become widely used in applications such as solar cells, light emitting diodes, and liquid crystal displays [2]. Indium tin oxide (ITO) is an In2O3-rich compound of In2O3 and SnO2 that has become the principal TCO material as a result of its excellent optical and electrical properties, having average sheet resistances of about 1 × 10-2 kȍ/ [2]. However, alternatives to ITO are being investigated because of the high cost and scarcity of indium. Antimony tin oxide (ATO) is a TCO material whose properties have been studied and looks to be a promising alternative to ITO due to its low cost [3-9]. This study proposes to promote the use of ATO by optimizing the fabrication of ATO thin films by solution-processing commercially-available ATO nanoparticles. EXPERIMENT ATO (Alfa-Aesar) 40-60nm nanoparticles were redispersed in water using tetramethylammonium hydroxide (TMAH) as a dispersing agent. The ATO powder was massed and combined with 10 wt.% TMAH solution (Sigma-Aldrich) in a ratio of 0.1823 ȝL of TMAH solution per mg of ATO [4]. Water was added to adjust the ATO dispersion concentration, and
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the dispersion was sonicated for 10 minutes and stirred until deposition. Dispersions of 0.1 wt.% and 5 wt.% were made. Microscope slides were cut into 1” x 1” substrates and cleaned using Kimwipes and pure water, acetone, and isopropyl alcohol. The substrates were treated with
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