Smart Windows: Electro‐, Thermo‐, Mechano‐, Photochromics, and Beyond

Abstract

A smart window that dynamically modulates light transmittance is crucial for building energy efficiently, and promising for on‐demand optical devices. The rapid development of technology brings out different categories that have fundamentally different transmittance modulation mechanisms, including the electro‐, thermo‐, mechano‐, and photochromic smart windows. In this review, recent progress in smart windows of each category is overviewed. The strategies for each smart window are outlined with particular focus on functional materials, device design, and performance enhancement. The advantages and disadvantages of each category are summarized, followed by a discussion of emerging technologies such as dual stimuli triggered smart window and integrated devices toward multifunctionality. These multifunctional devices combine smart window technology with, for example, solar cells, triboelectric nanogenerators, actuators, energy storage devices, and electrothermal devices. Lastly, a perspective is provided on the future development of smart windows.

3D Printed Smart Windows for Adaptive Solar Modulations

“…For the pure VO 2 samples, the solar modulation ability of VO 2 ‐polymer composite structure stands out from all the other reported data with a Δ T sol of 25.8% and a competitive T lum = 43.3%. [ 4,7 ] As for the W‐doped VO 2 samples, the Δ T sol of 23.3% outperforms all the previous reported results as shown in Figure a, where the previously reported data were categorized depending on the doping elements. [ 40–50 ] Since it is always a trading‐off relationship between T lum and Δ T sol , compared with the other reported performance, our W‐doped VO 2 ‐polymer composite sample gives one of the most promising combinations of T lum = 40.8% and Δ T sol = 23.3%.…”

“…[ 4–6 ] Smart windows are categorized as electrochromic smart window, photochromic smart window, mechanochromic and thermochromic smart window, based on the different stimulation sources as summarized in recent review. [ 7 ] Thermochromic smart windows are usually considered as a promising technology due to passive response, rational stimulus, easy fabrication, simple configuration and cost‐effective materials. [ 8–11 ]…”

The Challenge for Building Integration of Highly Transparent Photovoltaics and Photoelectrochromic Devices

“…Table 1, as reported hereafter, shows a synoptic comparison between different chromogenic technologies and semi-transparent PVs for integration in architectural glazing. Additional smart technologies (thermochromic [138][139][140] and photochromic [141][142][143][144] materials) have been added, for a broader and more complete comparison, even if they have not been widely considered in the review. Photochromic and thermochromic materials, when compared to the technologies discussed in this work, in fact, have the undoubted advantage of being able to guarantee the modulation of the spectral properties of the glass, according to an external stimulus (incident solar radiation and temperature, respectively), with simple deposition processes: in fact, the deposition of a single, thin film would be sufficient for obtaining the desired behavior (taking into account several process aspects, like the thickness of the film, concentration of molecules, intrinsic properties of the material used, etc.…”

Dual Thermal-/Electrical-Responsive Luminescent ‘Smart’ Window

“…The built environment is a large consumer of electricity, with 76% being spent in residential and commercial buildings [1], around half of this on electricity for heating/cooling and lighting [2]. One way to reduce the amount of energy spent on heating and cooling is by controlling the amount of incoming sunlight using "smart windows" [3,4] which can change their transmissivity in response to stimuli, including heat [5][6][7], electricity [4,8,9] and light [10][11][12]. In addition, using excess sunlight to generate electricity can even result in energy-generating windows [13][14][15].…”