Photoelectrochromism of Semiconductor Heterojunction All‐Solid‐State Electrochromic Device

Photoelectrochromism, combining autonomous environmental adaptation of photochromism with accurate control of electrochromism in one system, is a desired strategy for dynamic optical modulation. Conventional photoelectrochromic systems are limited by poor photochemical stability and electrochemical reversibility, which results from the incompatibility between photogenerated carriers and electrochemical doping equilibrium. Herein, instead of an electrochemical system, a semiconductor heterojunction composed of the C‐rich carbon nitride conjugated polymer (CPCN) and TiO 2 nanocrystals with the configuration of TiO 2 /CPCN/TiO 2 is used to fabricate an all‐solid‐state electrochromic device. The working mechanisms, performances, and enabled functionalities are investigated and evaluated. The device exhibits high optical modulation contrast exceeding 80%, rapid coloration response within 1 s as well as great stability, and achieves light‐triggered functionalities, such as light‐controlled transmittance modulation, high‐resolution photochromic image display and photo‐writing.