Black‐to‐Transmissive Electrochromism in π‐Conjugated Polymer‐Based Materials and Devices

Abstract

Electrochromic (EC) materials can exhibit reversible changes in their light absorption properties within the entire electromagnetic spectrum via redox reactions induced by the application of a low voltage on the order of a fraction of a volt to a few volts, holding great potential in many commercial applications, including smart windows, rear‐view mirrors, protective eyewear, and electronic paper. Of all EC materials, black EC materials, especially those that can reversibly switch between black and transmissive states, have attracted considerable attention in the research field of electrochromism, because of their significant usefulness for a number of commercial applications especially in smart windows and displays, as well as the tremendous challenges in their preparations and improvements. In recent decades, numerous black EC materials and devices, including neutral‐state black to oxidized‐state transmissive (black‐to‐transmissive) and oxidized‐state transmissive to neutral‐state black (transmissive‐to‐black), have been created in studies. This review focuses on the development of black‐to‐transmissive electrochromism in π‐conjugated polymer‐based EC materials from the perspective of the realization methodology, containing the donor–acceptor approach and physical color mixing strategy. A conclusion and an outlook are presented to point out the challenges and perspectives for further study of black‐to‐transmissive electrochromism in π‐conjugated polymer‐based materials and devices.