Influence of VO2 based structures and smart coatings on weather resistance for boosting the thermochromic properties of smart window applications

Abstract

Vanadium dioxide (VO₂)-based energy-saving smart films or coatings aroused great interest in scientific research and industry due to the reversible crystalline structural transition of VO₂ from the monoclinic to tetragonal phase around room temperature, which can induce significant changes in transmittance and reflectance in the infrared (IR) range. However, there are still some obstacles for commercial application of VO₂-based films or coatings in our daily life, such as the high phase transition temperature (68 °C), low luminous transmittance, solar modulation ability, and poor environmental stability. Particularly, due to its active nature chemically, VO₂ is prone to gradual oxidation, causing deterioration of optical properties during very long life span of windows. In this review, the recent progress in enhancing the thermochromic properties of VO₂-hybrid materials especially based on environmental stability has been summarized for the first time in terms of structural modifications such as core-shell structures for nanoparticles and nanorods and thin-films with single layer, layer-by-layer, and sandwich-like structures due to their excellent results for improving environmental stability. Moreover, future development trends have also been presented to promote the goal of commercial production of VO₂ smart coatings.

Scheme 1. Overview of VO₂-based composites on durability against a harsh environment.

Fig. 1. (a) Experimental flow chart for the synthesis of VO₂@ZnO core–shell structure nanoparticles and VO₂@ZnO films. (b) TEM images of VO₂@ZnO core–shell structure nanoparticles. Optical transmittance spectra of (c) uncoated VO₂ and (d) VO₂@ZnO. Reproduced with permission copyright © 2017, American Chemical Society. (e) Flow chart for the whole process of flexible film preparation and influence of reaction parameters for depositing MgF₂ on the surface of the VO₂ core. (f) TEM images of VO₂ nanoparticles with different shell thicknesses of VO₂@MgF₂. Vis-IR transmittance spectra of the VO₂ core. (g) Curves of visible light transmittance and the transmittance difference (ΔT) between room and high temperature at λ = 1200 nm of these samples with the change of treatment time. Reproduced with permission Copyright © 2019, American Chemical Society. (h) SEM image of the sample. (i) Preparation of VO₂ and AlO. (j) Transmittance spectra with different time spans. Reproduced with permission Copyright © 2017, Elsevier.

Fig. 2. (a) Preparation procedure for VO₂@SiO₂ nanoparticles and flexible composite films. (b) TEM images of the VO₂@SiO₂ composite film. (c) Transmittance spectra of coated and un-coated samples. Reproduced with permission Copyright © 2012, The Royal Society of Chemistry. (d) Preparation process of VO₂ and AA-VO₂. (e) TEM images of VO₂ nanoparticles and AA-VO₂. (f) Transmittance spectra with time in days. (g) Transmittance spectra with time in seconds. Reproduced with permission Copyright © 2019, American Chemical Society.

Fig. 3. (a) Experimental flow chart for the synthesis of the vanadium dioxide rod structure. (b) SEM images of VO₂@SiO₂ rod structure nanoparticles. (c) Exo and endo curves with different temperatures. Reproduced with permission Copyright © 2013, The Royal Society of Chemistry. (d) Flow chart for the whole process of VO₂(M)–Zno dandelions. (e) TEM images of VO₂(M)–Zno dandelions. (f) Thermochromic graph at different times for Zno nanoparticles and VO₂–Zno. Reproduced with permission Copyright © 2016, The Royal Society of Chemistry. (g) SEM images of pore, VO₂(M) and SiO₂. (h) Transmittance spectra of VO₂(M)@SiO₂. Reproduced with permission Copyright © 2013, Elsevier.

Fig. 4. (a) Preparation of the VO₂@anatase composite. (b) SEM images of the VO₂@anatase composite. (c) Transmittance spectra of VO₂@anatase. Reproduced with permission Copyright © 2013, The Author(s). (d) Preparation of V₂O₅/VO₂ seeding via a one-step high-powered impulse magnetron sputtering process. (e) SEM images of the amorphous V₂O₅ matrix. (f) Transmittance spectra of V₂O₅/VO₂. (g) Amorphous V₂O₅/VO₂ process. Reproduced with permission Copyright © 2022, Elsevier.

Fig. 5. (a) Experimental flow chart for the synthesis of VO₂@ZnO core–shell structure nanoparticles and VO₂@ZnO film. (b) TEM images of VO₂@ZnO core–shell structure nanoparticles. (c) Optical transmittance spectra of VO₂@ZnO at a constant temperature (60 °C) and humidity (90%). Reproduced with permission Copyright © 2019, Elsevier. (d) Flow chart for the whole process of VO₂@PMMA film preparation. (e) Solar modulation of the VO₂@PMMA film. Reproduced with permission Copyright © 2020, Elsevier.

Fig. 6. (a) Experimental flow chart for the synthesis of the V₂O₃/VO₂ bi-layer structure and (b) SEM images of the V₂O₃/VO₂ bi-layer structure. (c) Transmittance spectra of 60 nm VO₂ at different times in hours. (d) 60 nm V₂O₃/VO₂ at different times in hours. Reproduced with permission Copyright © 2018, Elsevier. (e and f) Flow chart for the whole process of VO₂/HfO₂ thin films by using the sputtering method and SEM images. (g) Graph of solar modulation ability versus aging time. (h) Durability of the fabricated films with the graph between optical contrast and aging time (days). Reproduced with permission Copyright © 2019, Elsevier. (i) Preparation of VO₂/SiO₂/TiO₂ thin layers. (j) TEM images of VO₂/SiO₂/TiO₂ thin layers. (k) Durability graph of the VO₂/SiO₂/TiO₂ thin film. Reproduced with permission Copyright © 2016, American Chemical Society.

Fig. 7. (a and b) SEM images of the deposited VO₂ thin film and comparison study between RFMS and HiPIMS. (c) Transmittance spectra of the thin film. Reproduced with permission Copyright © 2016, Elsevier. (d) Preparation of films such as single layer as G/VO_x, triple-layer as G/SiN_x/VO_x/SiN_x, and multi-layer. (e) SEM images of the as synthesized films. (f) Optical transmittance spectra of the films. (g) Solar modulation of the triple layer. Reproduced with permission Copyright © 2017, Elsevier.

Fig. 8. (a) Preparation of SiN_x/VO₂(SV), VO₂/SiN_x (VS), and SiN_x/VO₂/SiN_x (SVS) multilayers by using the reactive magnetron sputtering method. (b) Field Emission Scanning Electron Microscopy (FE-SEM) of the multilayers. (c) Durability graph of the SVS film at 60 °C and humidity of 90%. (d) Comparison graph of the aging test. Reproduced with permission Copyright © 2018, Elsevier. (e) Preparation of the sandwiched structure of Cr₂O₃/VO₂/SiO₂ (CVS) on a glass substrate by using the magnetron sputtering process and SEM images. (f) Fatigue test of simple VO₂ and structures. (g) Comparison graph of single VO₂ layer and SVS layers. Reproduced with permission Copyright © 2017, Elsevier. (h) SEM image of the as prepared sandwiched structure of WO₃/VO₂/WO₃ on VO₂ by using the medium frequency reactive magnetron sputtering technique (MFRMST) and HRTEM images. (i) Durability graph of the prepared layer under different temperature and humidity conditions. (j) Aging test of the VO₂ sample and thin-film WO₃/VO₂/WO₃. Reproduced with permission Copyright © 2016, The Royal Society of Chemistry.

Muhammad Khuram Shahzad

Rashid Ali Laghari

Syed Sohail Akhtar