High-performance black electrochromic devices using benzothiadiazole viologen and trisaminocyclopropenium perchlorate with extremely low transmittance and good stability

To minimize the colored state transmittance of the device in the ultraviolet–visible (UV–Vis) region (300–800 nm), we applied the idea of spectral complementary absorption to design electrochromic devices with transparent to black transition. Benzothiadiazole viologen (BV) and trisaminocyclopropenium ions (TAC) organic materials with dark blue and red coloration states were selected to prepare electrochromic devices with extremely low transmittance, here TAC is used as electrochromic material for the first time. The electrochromic devices do not require any supporting electrolytes . By controlling the concentration ratio of two materials, we achieved the ultra-low transmittance (0.33%), extremely low relative luminance (%Y L  = 0.12%), and fairly high coloring efficiency (341.9 cm 2 /C) of the TB-1 (0.05 mol/L TAC, 0.05 mol/L BV) device. Meanwhile, the TB-2 (0.0375 mol/L TAC, 0.05 mol/L BV) device possesses high transmittance contrast (81.79%) and very good long-cycle stability (4000 cycles, 96.1%).