Thermal conductivity of ITO and FTO thin films as a function of film thickness. The inset shows an example time-domain thermoreflectance curve and its best fit.

Research highlight: Patrick Hopkins group at the University of Virginia

Thermal Conductivity of Transparent Conducting Oxides

Visibly transparent and electrically conductive oxides are attractive for a wide array of applications. Indium tin oxide (ITO) and fluorine tin oxide (FTO) are a subset of the larger transparent conducting oxide family and possess transmittance in the visible spectrum as well as high electrical conductivity. Even though their unique optical and electrical properties have been thoroughly examined, the thermal transport properties, namely thermal conductivity in the cross-plane direction, have received much less attention. In this work, using a series of ITO and FTO thin films comprising a range of thicknesses and grain sizes, the cross-plane thermal conductivity is characterized using time-domain thermoreflectance. The heat capacity of the FTO films from simultaneous measurements of volumetric heat capacity and thermal conductivity on an ∼396 nm thick FTO film is also determined. It is shown that size effects have a considerable influence on the thermal conductivity from both the perspective of grain boundary and thin film scattering. Considering the depreciation of efficiencies at elevated temperatures of technologies reliant on TCOs, this work should provide critical insight into device design for those reliant on this unique subset of materials. Full details of the recently published work can be found here.

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