A mixed conducting polymer with an alternating ion-electron backbone was designed and synthesized to construct continuous percolating pathways for ion/electron transport and to reduce the electrode/electrolyte interfacial energy barrier, achieving intrinsically coupled ion-electron transport. The resulting quasi-solid-state electrochromic device seamlessly integrates fast switching, high optical contrast, ultra-long cycling stability with photo/thermal management, energy storage, and visual output, establishing a molecular engineering paradigm for advanced optoelectronic systems.