From a highly branched design to multiple functionalities proof of concept: rigid/flexible electrochromic prototypes with integrated energy storage capabilities

This study transitions from fundamental to applicative-focused, comparative evaluations of three highly branched conjugated polymers incorporating triphenylamine, fluorene, and thiophene in different ratios, displaying an optimized balance between the electrochromic and energy storage outcome. The electrochromic colour changes, colouring efficiency, overall capacitance, and non-Faradaic diffusion balance highly depend on the number of branching centres. The polymer having the highest branching density and shortest linear segments showed higher conductivity, superior redox stability, greater specific areal capacitance, and shorter electrochromic switching times. Charge-discharge experiments highlighted combined diffusion and capacitive features, pointing towards a hybrid, battery-type capacitor performance. Laboratory-scale prototypes employing the best-performing polymer were manufactured on a rigid or flexible structure. They delivered convincing electrochromic yields, especially for the rigid device: 2.95 s colouration, 4.95 s bleaching, 16.5 % maximum optical contrast, 195 cm 2 C −1 colouring efficiency, and a 5.5 % efficiency decay after 500 cycles. The same prototype showed notable energy storage characteristics: 0.58 mF cm −2 (CV, 5 mV s −1 scan rate) and 0.22 mF cm −2 (GCD, 0.02 mA charging current) specific areal capacitance, 95.06 % Coulombic efficiency, 400 μW cm −2 power density and a 6.01 % capacitance decay after 150 cycles. • Branched conjugated polymers: triphenylamine, fluorene, thiophene, different ratios. • Optimized balance between electrochromic performance and energy storage outcome. • Combined diffusion and capacitive features: a hybrid, battery-type capacitor. • High optical contrast, good colouring efficiency, low efficiency decay. • Good specific areal capacitance, high Coulombic efficiency, low capacitance decay.