Ferrocene-Functionalized Fulleropyrrolidine Derivative: A Performance Enhancer for Solid-State Electrochromic Devices

A custom-designed ferrocene-functionalized fulleropyrrolidine derivative Fullerene-Fc has been synthesized, which proves to be a feasible material to improve the performance of solid-state electrochromic devices. The molecule can be used as a dopant to design devices on substrates of rigid (glass) as well as flexible (PET) nature. The switching speed of devices made using poly(3-hexylthiophene) and ethyl viologen could be improved to display a switching time of less than 1 s when the Fullerene-Fc molecule was added. The improvement in the performance of the electrochromic device is likely due to the solution processability of the Fullerene-Fc molecule compatible with other used electrochromic active materials, which helps to facilitate the necessary charge carriers for the redox reaction within the device. Additionally, a coloration efficiency of more than 350 cm²/C and cyclic stability of up to 500 s were shown by the device with a color contrast of more than 40%. Furthermore, the Fullerene-Fc molecule in the P3HT/EV device can be incorporated to fabricate an all-organic flexible device. The charge storage properties of fullerene and the redox behavior of ferrocene make it a good choice to be used as an electrochromic performance enhancer.