RGB-to-black multicolor electrochromic devices enabled with viologen functionalized polyhedral oligomeric silsesquioxanes

Here we demonstrate multicolor electrochromic transitions of viologen functionalized polyhedral oligomeric silsesquioxanes (POSS-viologens). Highly efficient RGB coverage, including black, was successfully achieved with POSS-viologen employed multi-stacked electrochromic devices (ECDs). We prepared octa-viologen functionalized POSS (OHV-POSS) with the insertion of thiophene (OTxHV-POSS) and phenyl (OPhHV-POSS) moiety. The single-layer ion gel ECDs exhibited outstanding electrochromic performances. OTxHV-POSS and OHV-POSS showed red (R) and blue (B) transitions, respectively, with high transmittance changes and superb coloration efficiency. Saturated green (G) was also obtained from the mixture of OPhHV-POSS and OHV-POSS. Furthermore, multi-stacked ECDs were implemented by combining the RGB coloration layers with multiple electrodes. The two-layer ECDs generated intermediate colors, which was fully translated into the color mixing theory. The three-layer device created real black with blackness L^∗ of 6.99, covering 12.9% of the NTSC color gamut. The unprecedented RGB-to-black multicolor coverage, not reported elsewhere, is attributable to the reversible color-switching at a low redox potential for extended cyclic operations. Current findings imply that carefully designed POSS-viologens offer a universal route to high-performance and stable multicolor ECDs, offering compatibility with various pixelized color-changing displays and smart windows.