Dual-functional electrochromic supercapacitor with black-to-transmissive switching and reliable specific capacitance evaluation

High-performance electrochromic supercapacitors require synchronous optimization of optical modulation and energy storage. Herein, a blending polymer film (Pr/Pc) was developed through the physical integration of complementary polymers, which generates a synergistic interaction that enhances charge injection and enables high intrinsic capacitance. Interestingly, the mass of the Pr/Pc film was calculated using mass-absorbance estimation methods based on the Lambert-Beer law and the film achieves a mass specific capacitance of 218.8 F‧g⁻¹ and an area specific capacitance of 10.8 mF‧cm⁻². Meanwhile, the Pr/Pc film exhibits reversible black-to-transparent switching with exceptional electrochromic properties. Based on this, an electrochromic supercapacitor prototype device assembled with a Pr/Pc film as the active layer exhibits a mass specific capacitance of 78.8 F‧g⁻¹, a coulombic efficiency of near 100 %, and excellent charging/discharging stability. In addition, the device is capable of switching between black-to-transmissive states with fast switching time and near 100 % optical contrast retention after 500 cycles during charging/discharging.