Electrochromic energy storage performance of highly branched conjugated polymers with variable structural composition

Three conjugated highly branched polymers incorporating variable amounts of functionalized propylenedioxythiophene (ProDOT), triphenylamine (TPA) and fluorene are proposed in the current work for use as dual functional electrode materials in energy storage smart window (ESSWs) devices. In a three-electrode setup, these polymers attained the highest areal specific capacitances of 1.77 mF·cm −2 at 10 mV·s −1 and 0.56 mF·cm −2 (69.42 F·g −1 ) at 0.02 mA. Two of the polymers, with a lower branching arrangement, showed a notably electrochromic (EC) efficiency of 567/606 cm 2 ·C −1 and extremely short coloration/bleaching times (0.22 s/0.55 s and 0.48/0.47 s). The polymer with the highest pseudocapacitive performance, which displayed an optimal macromolecular packaging and better electroactivity ensured by the balanced content of TPA and ProDOT units, was selected for use as electrode material in ESSW prototypes with a glass(PET)/ITO/polymer//gel electrolyte/PEDOT:PSS/ITO/glass(PET) configuration. Notably, the capacitances consistently increased up to 2.07 mF·cm −2 (43.93 F g −1 ) at a charging current of 0.01 mA with the contribution of PEDOT:PSS in the ESSW prototype, which delivered a power density of 1.47 μW·cm −2 (50000 W·kg −1 ) at 1 mA, and a Coulombic efficiency of 98.5 %, albeit 47 % capacitance decay after 500 cycles. This also exhibited a coloration efficiency of 435 cm 2 ·C −1 , fast coloration/bleaching times of 0.57/2.27 s, a luminous transmittance modulation of 35.73 %, and only 1 % relative decay of the transmittance variation at 395 nm after 500 cycles. These findings underscore the potential of HB polymers as dual-functional electrode materials in ESSWs, as well as the possibility of performance modulation through structural composition. • Highly branched polymers are investigated as dual functional electrode materials. • Thin coatings obtained therefrom show interconnected grains morphology. • In three electrode set-up, electrochromic efficiency of 567/606 cm 2 ·C −1 is obtained. • The electrochromic and capacitive functions are demonstrated in flexible/rigid devices. • Coloration efficiency of 435 cm 2 ·C −1 and power density of 1.47 μW·cm −2 are obtained.