Highly Thermoelectric ZnO@MXene (Ti₃C₂T) Composite Films Grown by Atomic Layer Deposition

Due to its unique high conductivity and flexibility, the two-dimensional MXene material (Ti₃C₂T) 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 Ti₃C₂T membrane by atomic layer deposition (ALD). Benefiting from the low-temperature deposition characteristics of the ALD technique, the ZnO@Ti₃C₂T composite films maintain the basic apparent morphology of the original films after the deposition. We reveal that the Schottky barrier formed between ZnO and Ti₃C₂T 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 Ti₃C₂T is found to reduce the thermal conductivity of the composite films by a factor of four as compared to pure Ti₃C₂T ones, further improving the overall thermoelectric properties of the ZnO@Ti₃C₂T 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.