Multiscale Synergistic Engineering of Constructed Devices Enables Ultrafast Real‐Time Dynamic Photochromic‐Electrochromic Optical Modulation

Abstract Photochromic–electrochromic dual‐responsive devices hold great promise for dynamic optical modulation and energy‐efficient smart systems. However, achieving rapid, reversible, and bidirectional color switching remains a significant challenge, limited by unbalanced charge transport and poor interfacial stability. Here, a multiscale synergistic design strategy is presented that integrates nanostructure engineering, charge transport regulation, and interface optimization. Molybdenum‐doped tungsten oxide quantum dots are composited with poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate to construct a dual‐responsive functional layer. Mo doping introduces additional oxygen vacancies in tungsten oxide lattice, enhancing electrochemical activity and facilitating coupled ion/electron transport within the composite. The engineered interfacial architecture suppresses charge accumulation, accelerating the photo response and enhancing the synergistic photoelectric performance. The device fabricated by integrating a functional layer and a hydrogel electrolyte between two indium tin oxide electrodes exhibit bidirectional optical control: under a −3 V bias, visible light‐induced coloration is enhanced, reducing transmittance from 19.6% to 10.5%; applying a +1.5 V bias enables ultrafast bleaching within 3 s—6 600 times faster than passive fading. Additionally, the device achieves a temperature drop of 10.25 °C, demonstrating its excellent passive insulation performance. This work offers a pathway toward next‐generation chromic devices with fast, reversible, and energy‐efficient performance for adaptive optoelectronics and sustainable building technologies.