ABSTRACT Electrochromic polymers (ECPs) offer promising applications in dynamic optical devices, but their operational stability is often compromised under overpotential stress. Here, we introduce a transparent, highly conductive interlayer of n‐doped poly(benzodifurandione) (n‐PBDF) between indium tin oxide and a representative 3,4‐propylenedioxythiophene based ECP‐Blue (ECP‐B). In its doped state, n‐PBDF is highly conductive, lowering interfacial resistance and supporting rapid charge injection. Upon de‐doping near +0.8 V, it transitions into a resistive barrier that restricts excessive charge flow. Charge density measurements further highlight this protective role as single‐layer ECP‐B accumulates ∼1.49 mC cm −2 more charge than the bilayer at +1.5 V, reflecting uncontrolled overoxidation, whereas the n‐PBDF/ECP layer suppresses it. Long‐term cycling confirms that ECP‐B loses redox activity under stress, while the bilayer retains the ECP‐B onset with a broadened n‐PBDF feature. Electrochemical impedance spectroscopy validates this voltage‐gated mechanism, showing low resistance at operational bias, a sharp rise (∼60%) during n‐PBDF de‐doping, and a resistive‐to‐capacitive transition above +1.2 V. Thin‐films spectroelectrochemistry indicates that the bilayer maintains optical contrast comparable to ECP‐B across the operating window and, under overpotential, limits additional loss, preserving ∼50% at +1.5 V.
Rout et al. (Wed,) studied this question.