Random donor‐acceptor conjugated copolymers with broad and even absorption across the visible region exhibit black neutral states and highly transmissive oxidized states. Polymer films show excellent optical contrasts, fast switching times, and long‐term redox switching stability. Additionally, the utility of this black‐to‐transmissive switching polymer in a window‐type electrochromic device has been demonstrated.

Poly[6,6′-bis(ethylene-3,4-dioxythien-2-yl)]-N,N′-dialkylisoindigo (PBEDOT-iI) was synthesized and incorporated as an electroactive material into electrochemical supercapacitors (ESCs) in type I and type III configurations. In type I ESCs, PBEDOT-iI provides a specific power of ∼360 W/kg and specific energy of ∼0.5 Wh/kg, while retaining about 80% of its electroactivity over 10 000 cycles. In addition, we report on the use of PBEDOT-iI in type III supercapacitors where operating voltages as high as 2.5 V were achieved with specific energies of ca. 15 Wh/kg, albeit with limited stability.

The continuing search for relevant structure–property relationships in the area of organic electronics is expected to impact both intrinsic material performance capability and the viability of their implementation in a broad range of device applications. Cathodically coloring π-conjugated polymer electrochromes represent a class of materials potentially attractive for low-cost and nonemissive flexible display devices including e-paper. Nonetheless, both the synthetic access to a full range of visible colors and the ability to produce solution-processable systems that switch rapidly and durably from a colored neutral state to a highly transmissive doped state upon electrochemical oxidation require that material structure–property relationships be carefully examined. In this report, we correlate molecular structure effects, redox properties, and electrochromic performance for a series of rationally designed neutral-state green polymers composed of electron-rich 3,4-dioxythiophene (DOT) units and the electron-deficient core 2,1,3-benzothiadiazole (BTD). While homopolymers synthesized from 3,4-alkylenedioxy-bridged monomers including 3,4-ethylenedioxythiophene (EDOT) and 3,4-propylenedioxythiophenes (ProDOT) have shown particularly desirable redox-switching properties in the early years of electrochromic polymer development, their “unbridged” dialkoxythiophene counterparts (DalkOTs) have not raised the same initial interest. Herein, it is shown that low band gap systems relying on DalkOT units and electron-deficient BTD cores could represent viable alternatives to their ProDOT-based counterparts in electrochemical devices involving green-to-transmissive switching electrochromes. Interestingly, provided the set of materials examined in this study, the long-term switching stability of the ProDOT-co-BTD system remains superior to that of its polymeric analog relying on DalkOTs – exhibiting less than 15% loss of contrast over 20,000 switching cycles (atmospheric conditions). Long-term cycle life is further demonstrated in a window-type device integrating the ProDOT-co-BTD system. DFT calculations performed at the B3LYP/6-31G** level suggest subtle variations in the energy-band structure of the polymer repeat-units and predict the existence of the dual band of optical absorption exhibited by the low-band gap polymers.

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We report on the electrochemical and capacitive behaviors of poly(2,2-dimethyl-3,4-propylene-dioxythipohene) (PProDOT-Me2) films as polymeric electrodes in Type I electrochemical supercapacitors. The supercapacitor device displays robust capacitive charging/discharging behaviors with specific capacitance of 55 F/g, based on 60 μg of PProDOT-Me2 per electrode, that retains over 85% of its storage capacity after 32 000 redox cycles at 78% depth of discharge. Moreover, an appreciable average energy density of 6 Wh/kg has been calculated for the device, along with well-behaved and rapid capacitive responses to 1.0 V between 5 to 500 mV s(-1). Tandem electrochemical supercapacitors were assembled in series, in parallel, and in combinations of the two to widen the operating voltage window and to increase the capacitive currents. Four supercapacitors coupled in series exhibited a 4.0 V charging/discharging window, whereas assembly in parallel displayed a 4-fold increase in capacitance. Combinations of both serial and parallel assembly with six supercapacitors resulted in the extension of voltage to 3 V and a 2-fold increase in capacitive currents. Utilization of bipolar electrodes facilitated the encapsulation of tandem supercapacitors as individual, flexible, and lightweight supercapacitor modules.