![]() Therefore, exploration of noncomplex and high-performance alternative materials is essential for achieving the switch from colorless to black. There are also some disadvantages: (1) low transmittance in transmissive states owing to the long conjugation and the intramolecular charge-transfer interactions and (2) more complicated synthesis method owing to harsh preparation, more by-products, and low yield. An effective strategy to solve this problem is integrating distinct chromophores in an individual molecule, such as a polymer 16- 18 or a copolymer, 19, 20 which can be achieved by incorporating it with twisted structures, a donor–acceptor design, and adjusted conjugated electrochromophores. ![]() 14, 15 However, the absolute redox potential was difficult to control in this strategy, and the mixture of multiple materials also yielded low transmittance in transmissive states. To date, colorless-to-black switching is mainly achieved by combining several desirable colors to achieve complementary absorption based on the color-mixing theory. However, achievement of colorless-to-black switchable devices still remains a challenging task due to the completely reversible absorption (transmittance) in transmissive and colored states. Among all color switching, 11- 13 the colorless-to-black switch is of technological significance since it can filter the light from an entirely transmissive state to a nearly opaque state in an effective way. ![]() 10 In developing chromic materials, it needs to include single colorations or superposition to recreate various desirable colors, which can extend the applicability. 1- 5 Chromic materials refer to a special kind of chemicals with the ability to reversibly change color when exposed to an external stimulus, such as light, 6 temperature, 7 pressure, 8 humidity, 9 and electrical field. Switchable materials have received considerable attention due to their potential applicability (i.e., displays, automotive, and building industries). These results contribute toward gaining an insightful understanding of the electrochemical process of perovskites and greatly promoting the development of switchable devices. In addition, the contrast ratio can be modulated over the entire visible region by changing the concentration and the applied voltage. By applying an appropriate voltage, the device undergoes reversible switching between colorless and black, which is attributed to the formation of lead and Br 2 in the redox reaction induced by the electron transfer process in MAPbBr 3. The perovskite solution can be used as the active layer to assemble the device, showing superior transmittance over the entire visible region in neutral states. Herein, we report on an electrochemical device that can switch between colorless and black by using the electrochemical process of hybrid organic–inorganic perovskite MAPbBr 3, which shows a high integrated contrast ratio of up to 73% from 400 to 800 nm. However, it still remains a challenge owing to the tremendous difficulties in the design of completely reverse absorptions in transmissive and colored states. Colorless-to-black switching has attracted widespread attention for smart windows and multifunctional displays because they are more useful to control solar energy. ![]()
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