**5. Concluding remarks and outlook**

In this chapter, we have elaborated the fabrication of nanoporous VO2 nanomaterials and the effect of porosity on enhancing the thermochromic properties. Compared with the other property enhancement methods, such as ARC multilayers, biomimetic patterning, nanothermochromism and periodic patterning (**Figure 8**), the porous design shows the advantages in easy-to-handling, low usage of VO2 materials as well as the thickness control, which could reduce the cost in the real applications. In the fabrication of nanoporous VO2 thin films, the PAD, freeze-drying as well as the dual-phase transformation are the three main methods for random nanoporous structures, while the colloidal lithography

**Figure 8.** Methods proposed for enhancing the thermochromic performance of VO2 nanomaterials [55].

with the MCC template is an effective approach for periodic nanoporous structures. The calculations reveal that the nanoporous structure could result in the decrease of optical constants and thus lead to the enhancement of visible transmission while maintain the decent solar modulating abilities.

Although many efforts have been dedicated to optimize the effect of nanoporous structure on enhancing the thermochromic performance of VO2 thin films, the low visible transmission (<~80%) and the low solar modulating ability (<~30%) restrict the real applications in thermochromic smart windows. From the viewpoint of materials design, the periodic nanoporous VO2 thin films with the periodicity below 100 nm should give rise to the largely enhanced visible transmission as well as the highly reduced scattering, which could greatly improve the thermochromic performance for smart window applications.
