Octa-viologen substituted polyhedral oligomeric silsesquioxane exhibiting outstanding electrochromic performances

Abstract

We present a new strategy for improving the electrochromic properties of single-layered ion gels for electrochromic devices (ECDs) by incorporating octa-hexyl viologen substituted polyhedral oligomeric silsesquioxane (OHV-POSS). Newly synthesized OHV-POSS was included in ion gel compositions containing a poly(vinylidene fluoride) copolymer and ionic liquid to produce a freestanding film. When applied in single-layered ECDs, due to high ionic conductivity and fast charge transfer, the OHV-POSS film exhibited outstanding electrochromic performances with low redox potentials at -1.1 V, high transmittance changes (Delta T) of 56.1%, and a moderate coloration efficiency (CE) of 124.1 cm(2)/C. When combined with isooctyl polyhedral oligomeric silsesquioxane (IO-POSS), the device performances were remarkably enhanced, exhibiting a Delta T of 67.2% and CE of up to 307.8 cm(2)/C. In addition, the fabricated device maintained its switching stability for up to > 12,000 cycles with a switching speed of 8.6 s. The electrochromic improvement is attributed to the presence of a POSS (Si-O-Si) cross-linkable cage structure featuring robust mechanical properties. In addition, flexible ECDs were fabricated on silver nanowire-PEDOT:PSS composite electrodes, and superb electrochromic performances were achieved with repeated bending cycles (> 200 cycles). This study's results present a promising tool for the material design of high-performance stable ECDs for long-term operation in displays, eyewear, and transmissive windows.