Electronic and Interfacial\nProperties of 2D MXene/Blue\nPhosphorene Heterostructures: Impact of External Strain for Thermoelectric\nApplications

Building two-dimensional (2D) van der Waals (vdW) heterostructures\nand enhancing their properties through strain engineering unlocks\nnew applications for their constituent materials. In this study, we\npresent a comprehensive first-principles investigation of oxygen-functionalized\nMXene-based heterostructures (M<sub>2</sub>CO<sub>2</sub>/blue phosphorene\n(blueP), M = Sc, Zr, Hf), emphasizing their structural, electronic,\nand thermoelectric properties under the application of various types\nof strain. Our results indicate a reduction in band gap under strain\nand metallic transition for in-plane strain (uni- and biaxial strain).\nTransition from type-I to type-II could be obtained for Hf<sub>2</sub>CO<sub>2</sub>/blueP and Zr<sub>2</sub>CO<sub>2</sub>/blueP heterostructures\nby applying strain, providing a method for their potential application\nin photocatalytic devices that require type-II band alignment for\nphotogenerated charge separation. We observe a positive correlation\nbetween strain and thermoelectric efficiency under most conditions\nwith a significant enhancement in the thermoelectric power factor\n(PF) and electronic figure of merit (ZT<sub>e</sub>) achievable in\nall heterostructures through strain engineering. Among the three heterostructures,\nSc<sub>2</sub>CO<sub>2</sub>/blueP showed the maximum PF and ZT<sub>e</sub> of 11.2 × 10<sup>11</sup> W/m K<sup>2</sup> s and 43.2\nfor 2% normal compressive strain and 4% biaxial compressive strain,\nrespectively. These findings suggest that MXene/blueP heterostructures\nhold significant promise for applications in optoelectronics and high-temperature\nthermoelectric devices.