Grass-like alumina enhances transmittance and electrical conductivity of atomic layer deposited Al-doped ZnO for thermoelectric and TCO applications
Tomi Koskinen, R. Ramesh, Ilkka Tittonen, Christoffer Kauppinen
Abstract
Transparent thermoelectric materials enable the integration of sensing and energy harvesting devices on various surfaces such as windows and user interfaces. A key constraint for device performance in such applications is the available surface area from which the thermoelectric power should be harvested without compromising the optical properties. Here, we demonstrate atomic layer deposition (ALD) of aluminum doped zinc oxide (AZO), the most prominent n-type thermoelectric material, on grass-like alumina (GLA), a high-performance, low-cost antireflective coating. The conformal nature of the ALD process enables the AZO growth to closely follow the topography of the underlying GLA film, therefore providing an increased effective surface area compared to a reference AZO film grown directly on plain glass. The films grown on GLA show an improved electrical conductivity attributed to additional doping by the GLA. The effect is pronounced at lower AZO thicknesses, resulting in a 228% increase in the electrical conductivity and an 80% increase in the thermoelectric power factor of 32 nm thick films. Moreover, the GLA-AZO films partly inherit the antireflective behavior of the GLA film, thus showing improved optical transparency compared to the reference AZO film on glass. Our results promote transparent thermoelectric devices with improved transparency and thermoelectric performance.