Misfit layered Ca3Co4O9 as a high figure of merit p-type transparent conducting oxide film through solution processing

Abstract

Ca3Co4O9 thin films synthesized through solution processing are shown to be high-performing, p-type transparent conducting oxides (TCOs). The synthesis method is a cost-effective and scalable process that consists of sol-gel chemistry, spin coating, and heat treatments. The process parameters can be varied to produce TCO thin films with sheet resistance as low as 5.7 kΩ/sq (ρ ≈ 57 mΩ cm) or with average visible range transparency as high as 67%. The most conductive Ca3Co4O9 TCO thin film has near infrared region optical transmission as high as 85%. The figure of merit (FOM) for the top-performing Ca3Co4O9 thin film (151 MΩ−1) is higher than FOM values reported in the literature for all other solution processed, p-type TCO thin films and higher than most others prepared by physical vapor deposition and chemical vapor deposition. Transparent conductivity in misfit layered oxides presents new opportunities for TCO compositions.