Author

Alex Miller

Date of Graduation

Spring 2013

Degree

Master of Science in Materials Science

Department

Physics, Astronomy and Materials Science

Committee Chair

Saibal Mitra

Keywords

pulsed laser deposition, electrochromic, tungsten oxide, optical properties, thin film device

Subject Categories

Materials Science and Engineering

Abstract

The goal of this work was to fabricate electrochromic devices made with pulsed laser deposited tungsten oxide films and evaluate the effects of material properties on device performance. The oxide films were deposited in O2 atmospheres from 10-3 - 10-1 mbar on ITO/glass substrates between room temperature (RT) and 450 °;C. A pulsed KrF laser operating at 248 nm was used to ablate the WO3 target. XRD analysis showed amorphous native films for RT depositions and orthorhombic poly-crystalline films deposited at 450°;C. UV-Vis spectroscopy showed transparent films deposited at 10-1 mbar and opaque films for lower chamber pressures. For depositions at RT, atomic force microscopy revealed ultra-smooth surfaces for films deposited at 10-2 mbar and disordered/porous surface morphology for films deposited at 10-1 mbar. With the substrate temperature at 450 °;C, the topography had visible grain patterns. IV measurements were done on films grown at different chamber pressures. Preliminary devices were constructed by sandwiching a drop of 2.0-M HCl between the oxide/ITO/glass and a top ITO/glass electrode. Cyclic voltammetry was used to automate the bias potential, determine charge insertion, and investigate response time and the effects of repeated cycles. Devices constructed with opaque oxygen-deficient or poly-crystalline tungsten oxide films displayed poor electrochromism while devices constructed with transparent amorphous WO3 films (deposited at 10-1 mbar and RT) exhibited electrochromic properties including a large optical modulation (76.1 %T at 705 nm) and a coloration efficiency of 11 cm2/C.

Copyright

© Alex Miller

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