Electrostatic-Force-Assisted Dispensing Printing of Electrochromic Gels for Low-Voltage Displays

Abstract

In this study, low-voltage, printed, ion gel-based electrochromic devices (ECDs) were successfully fabricated. While conventional dispensing printing provides irregularly printed electrochromic (EC) gels, we improved the adhesion between the printed gel and the substrate by applying an external voltage. This is called electrostatic-force-assisted dispensing printing. As a result, we obtained well-defined, printed, EC gels on substrates such as indium tin oxide-coated glass. We fabricated a gel-based ECD by simply sandwiching the printed EC gel between two transparent electrodes. The resulting ECD, which required a low coloration voltage (∼0.6 V), exhibited a high coloration efficiency (η) of 161 cm/C and a large transmittance contrast (∼82%) between the bleached and colored states at -0.7 V. In addition, electrostatic-force-assisted dispensing printing was utilized to fabricate directly patterned ECDs.

Asymmetric molecular modification of viologens for highly stable electrochromic devices

“…The device colored at À1.2 V required a longer bleaching time due to the higher concentration of BHV + c, similar to the viologenbased Type I ECDs. 33,40,41 Coloration efficiency (h) values were compared at various voltages. The h is dened by h ¼ DOD/DQ ¼ log(T b /T c )/DQ, where DOD is the optical density contrast calculated by the logarithm of the transmittance ratio of bleached (T b ) and colored (T c ) states, and DQ is the amount of injected charge.…”

All-in-One Gel-Based Electrochromic Devices: Strengths and Recent Developments

“…Other approaches, taking advantage of the exceptional properties of ionic liquids (ILs) (e.g., high ionic conductivity, negligible vapor pressure, high boiling point, wide operating potential window, good compatibility with organic solvents, and good chemical and thermal stability [ 63 , 84 , 85 , 86 ]), replace the current solvent of the electrolytes in ECDs [ 63 , 86 ]. Accordingly, ILs have been combined with conventional polymers (e.g., polyvinyl alcohol (PVA) [ 84 , 87 ] or PMMA [ 85 , 88 ]), copolymers in well-known ion gels (e.g., PVDF-co-HFP) [ 89 , 90 , 91 , 92 , 93 , 94 , 95 ], or gelatin in so-called ion jelly [ 44 ], achieving ionic conductivities up to 1 × 10 −3 s cm −1 [ 85 ]. Subsequently, an approach based on synthesizing new functional polymers by polymerizing poly(ionic liquid) (PIL) monomers [ 86 , 96 , 97 , 98 , 99 ], in some cases using ILs as liquid solvent [ 86 , 97 ], led to ionic conductivities as high as 1 × 10 −2 s cm −1 [ 97 ], and they have been used as promising electrolytes in ECDs.…”

“…More recently, Kim et al reported an innovative process that provides well-defined directly patterned ECDs without the use of photolithography, also based on ion gels. The rubbery and self-standing consistency of the EC gels allows them to be directly printed on the electrode substrate while maintaining dimensional stability [ 90 ]. They used the so-called electrostatic force-assisted dispersing printing method, where controlled applied potential between the electrode substrate and the printer nozzle during the deposition process enhances the dimensional stability and adhesion by electrostatic interactions (between the negatively charged substrate and the positively charged ion gel surface) ( Figure 15 a).…”

“… ( a ) Schematic illustration of electrostatic force–assisted dispensing printing and printed EC gel; ( b ) photographs of ECDs comprising EC gels printed by this technique with different shapes: ECDs in their ( I , III ) bleached state (left) and ( II , IV ) colored state upon applying a redox voltage of −0.8 V (right). Adapted with permission from [ 90 ], copyright (2017) American Chemical Society. …”

Transparent-to-dark photo- and electrochromic gels

“…Gel electrolytes are clearly a desirable feature of these devices, as this reduces issues of leaking for example in case of a fault in the device. Gel electrolytes have been reported as part of electrochromic devices 2,14,15 . However, there are no examples to the best of our knowledge where the gel matrix itself has been shown to be an effective means of forming transparent-to-black smart windows; in this case, neither the bleached nor the colored state is soluble, nor does either coat an electrode.…”