Colorless to black switching with high contrast ratio via the electrochemical process of a hybrid organic–inorganic perovskite

Abstract Colorless‐to‐black switching has attracted widespread attention for smart windows and multifunctional displays because they are more useful to control solar energy. However, it still remains a challenge owing to the tremendous difficulties in the design of completely reverse absorptions in transmissive and colored 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. 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. 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 . In addition, the contrast ratio can be modulated over the entire visible region by changing the concentration and the applied voltage. These results contribute toward gaining an insightful understanding of the electrochemical process of perovskites and greatly promoting the development of switchable devices.