A Viologen/α-MnO₂ Inorganic/Organic Hybrid Assembly-Based Solid-State Electrochromic Device: Improved Performance and Multiwavelength Switching

Perturbation-induced reversible color modulation materials are highly sought after in smart systems, which are useful for various applications, with significant interest in multiwavelength switchability. Nevertheless, the majority of current electrochromic technology, one member of the family, only offers single-wavelength optical switchability; it is still difficult to achieve multiwavelength-based color switchability using straightforward methods especially in inorganic materials. Here, an inorganic–organic hybrid electrochromic device was fabricated by combining the electrochemically deposited MnO2 electrode with drop-casted viologen gel. This combination exhibits different advantages like multiwavelength switching, high color contract, better stability, and fast response. The hybrid device shows multiwavelength (600 and 730 nm) color switching. The organic–inorganic electrochromic device switches from pale yellow to dark blue reversibly under an external perturbation of ±1.5 V with a fast coloration/bleaching time of 2 s/4.3 s at 600 nm. The in situ electrochemical measurements show that the hybrid device shows a high optical contrast of 90% and a change in transmittance of 21% at 600 nm (midwavelength of the visible region) and 730 nm (end-edge wavelength of the visible region), respectively, with excellent electrochromic stability at both wavelengths. Also, the device exhibits a high value of coloration/bleaching efficiency (112/380 cm2/C @600 nm and 35/80 cm2/C @730 nm). These results provide a pathway to improve the electrochromic performance of a single-layered device by combining it with complementary electrode materials for practical applications in smart windows.