AVS 53rd International Symposium
    Thin Film Wednesday Sessions
       Session TF-WeA

Paper TF-WeA1
Na Doped V@sub 2@O@sub 5@ Thin Films for the Thermoelectric Device Applications

Wednesday, November 15, 2006, 2:00 pm, Room 2022

Session: Thin Films for Energy Applications in Photovoltaics, Fuel Cells, Hydrogen Storage & Batteries
Presenter: S. Iwanaga, University of Washington
Authors: S. Iwanaga, University of Washington
M. Marciniak, University of Washington
R.B. Darling, University of Washington
F.S. Ohuchi, University of Washington
Correspondent: Click to Email
The thermoelectric properties of bronze-like V@sub 2@O@sub 5@ thin films were investigated above room temperatures. The potential utilization of these materials for thin film based thermoelectric devices were considered. The original motivation for this research came from the fact that V@sub 2@O@sub 5@ exhibits an unusually high Seebeck coefficient of about -550 µV/K; however, low electrical conductivity (@sigma@ ~ 1E-4 @OMEGA@cm) hinders its usage as a thermoelectric material in practical applications. Systematic doping of Na into the V@sub 2@O@sub 5@ host lattice was investigated in an attempt to find the conditions that maximize a power factor described by @sigma@S@super 2@, where @sigma@ and S are the electrical conductivity and Seebeck coefficient, respectively. The Na doped V@sub 2@O@sub 5@ solutions were made by the melt-quench method, which provides very stable solutions that lasts for months. The solution was then coated on quartz substrates. It was experimentally shown that proper annealing of Na doped V@sub 2@O@sub 5@ thin films dominantly produce @beta@-Na@sub 0.33@V@sub 2@O@sub 5@. The electrical conductivity was increased by a factor of about 1000, while the Seebeck coefficient decreased to ~40 % of the original value, resulting in an improvement of the power factor by a factor of about 160. These improved thermoelectric properties were further studied by current-voltage (I-V) measurements. The I-V measurements were performed while applying a temperature gradient to the film by applying a current source in such a way that the thermopower current was suppressed by applying the current in the opposite direction. The I-V characteristics at different applied @DELTA@T were thus obtained, from which the output power was calculated from the I-V data. The Na@sub 0.33@V@sub 2@O@sub 5@ thin films were used in a sensor application and their performance was evaluated.