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

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. The smart window is a promising technology to reduce building energy consumption by dynamically controlling the indoor solar irradiation. In this review, the most recent progress in strategies for electro‐, thermo‐, mechano‐, and photochromics is summarized. A summary of integrated devices toward multifunctionality is presented as well as a perspective on future development.