Two-dimensional VO₂ nanosheet converted from MXene for flexible thermochromic smart windows

Vanadium dioxide (VO2) has attracted considerable attentions owing to its unique phase-transition based thermochromic (TC) feature, which make it promising for energy-saving smart windows. For large-scale integration to ubiquitous applications, it is highly desirable to develop a simple and efficient casting technique of a reliable VO2 thin film with enhanced TC performance. However, a significant challenge lies in achieving consistent TC performance when casting VO2 thin film on diverse non-planar surfaces. Herein, we report the fabrication of twodimensional (2D) monoclinic-phase VO2 nanosheet through the oxidation of single-layer V2CTx nanosheet. Benefitting from the high packing density of the 2D morphology, uniform thin film composed solely of VO2 nanosheet can be directly casted on various surfaces. Moreover, the tightly bound nanosheets ensure remarkable phase-transition and significantly reduced optical scattering. As a result, the VO2 nanosheet thin film exhibited excellent TC performance, including NIR switching of 62.2 %, luminous transmittance of 45.7 %, and solar modulation efficiency of 16.9 %. The VO2 nanosheet was further integrated into flexible and large-area TC smart window, demonstrating great promise for practical applications in thermal management. This study highlights the significance of the 2D morphology of VO2 in enhancing TC performance and phase-transition, offering valuable insights for future advancements in optoelectronic applications.