Highly Thermoelectric ZnO@MXene (TiCT) Composite Films Grown by Atomic Layer Deposition.

Due to its unique high conductivity and flexibility, the two-dimensional MXene material (TiCT) is expected to possess great potential in the thermoelectric field. However, the low thermoelectric performance from high thermal conductivity and a low Seebeck coefficient has limited its practical application. In this report, we demonstrate the uniform growth of ZnO layers on the laminar TiCT membrane by atomic layer deposition (ALD). Benefiting from the low-temperature deposition characteristics of the ALD technique, the ZnO@TiCT composite films maintain the basic apparent morphology of the original films after the deposition. We reveal that the Schottky barrier formed between ZnO and TiCT exhibits an energy-filtering effect, significantly enhancing the Seebeck coefficient to result in more than a double increase in the power factor. Meanwhile, the strong phonon-interface scattering between ZnO and TiCT is found to reduce the thermal conductivity of the composite films by a factor of four as compared to pure TiCT ones, further improving the overall thermoelectric properties of the ZnO@TiCT composite films. Our investigation provides an ALD-based strategy for growing wide band gap layers on the narrow band gap films to improve the thermoelectric performance of various MXene materials.