Cation-Conditioned Oxidative Doping Enables Durable Near-Infrared Polymer Electrochromism

Abstract Oxidation of p-type conjugated polymers is compensated by anions, but their electrochromic response can also depend on electrolyte cations. Here, electropolymerized P(TAA-OC-TAA) is used to distinguish its intrinsic neutral–polaron–bipolaron evolution from cation-dependent state accessibility and reversibility. In situ UV–vis–NIR and Raman spectroscopy, impedance measurements, and density functional theory calculations show that cation composition alters interfacial kinetics and the local doping environment without changing the fundamental redox pathway. A mixed Li+/Zn2+ (Li–Zn) electrolyte affords 71.2% near-infrared modulation, with only a 3.7% decrease in the transmittance window after 1300 cycles. Controls using P3HT and PTTPA polymers and a Na+/Zn2+ (Na–Zn) electrolyte show that performance depends on cation–polymer matching rather than ion mixing alone. A complementary P(TAA-OC-TAA)/PBFDO device retains 88.75% of its initial optical modulation after 9000 switching cycles, demonstrating that electrolyte cation control can translate charge-state regulation into durable device-level electrochromism.