Ionic additive in an ionogel for a large area long lived high contrast electrochromic device

Heptyl viologen (HV) based electrochromic devices (ECD) suffer from poor write-erase efficiencies and become permanently colored after a few redox switches, thus limiting their use as electrochromic windows or mirrors. This formidable issue is addressed by incorporating an ionic additive: a disodium salt of ethylenediamine tetra acetic acid (EDTA), in the ionogel electrolyte. EDTA, via electrostatic interactions, binds to the HV+center dot radical cation and prevents its' further reduction to the undesirable pale colored neutral HV0, by wedging in-between the moieties and inhibiting their undesirable stacking. A large area HV/EDTA in gel/Prussian blue (PB) ECDs of similar to 8 cm x 6 cm dimensions outperforms the HV/gel/PB ECD which is evidenced in the enhanced transmission modulation (Delta T-max: 73.1% at 606 nm), coloration efficiency (eta: 346.2 cm(2) C-1) and superior chromaticity coordinates (colored: L*,a,b: 40, 10,-65) compared to lower magnitudes of 69.2%, 270.3 cm(2) C-1 and (L*,a,b: 50.3, 8,-48.5) respectively. When evaluated as a mirror, HV/EDTA in gel/PB ECD shows a reflectance modulation of similar to 65% which does not alter significantly, even at -10 degrees C or at +60 degrees C, ratifying its thermal robustness. The HV/EDTA in gel/PB ECD shows color and bleach times of 16 and 35 s, retains similar to 93% of its' initial contrast after 10(4) cycles and after aging for 2 years, continues to deliver a transmission modulation of 68%. This study successfully demonstrates a cost effective, easily implementable, scaled-up HV/EDTA in gel/PB based long-lived durable ECD for energy efficient smart window and rearview mirror applications.

Automated summary

The addition of a disodium salt of ethylenediamine tetra acetic acid (EDTA) to the ionogel electrolyte addresses the issue of poor efficiency and undesirable stacking in Heptyl viologen (HV) based electrochromic devices, resulting in improved performance metrics and thermal robustness.