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Page 14 of 22 Wu et al. Soft Sci 2024;4:29 https://dx.doi.org/10.20517/ss.2024.21

Figure 9. Recent advances in electrolyte pattern design. (A) Flexible and self-powered ECD with electrolyte pattern by connecting the
hydrogel pen with EC film by Al wire. Reproduced with permission [21] . Copyright 2023, SPJ; (B) Stretchable ECD with screen-printed
patterned electrolyte. Reproduced with permission [50] . Copyright 2020, Springer Nature; (C) Flexible ECD with 3D direct printed
patterned UV-curable electrolyte. Reproduced with permission [20] . Copyright 2022, Wiley-VCH. ECD: Electrochromic display; EC:
electrochromic; UV: ultraviolet.

current electrolyte patterning design mainly relies on UV curing-based methods, which has potential issues
with precise controllability of pattern resolution due to the dimensional changes after curing. Besides, the
limited penetration depth of UV light may also influence the uniformity of the patterned electrolyte,
especially for the thicker one.

ECD pixel design
Generally, the pixelated ECDs are composed of one or more subpixels with the designed arrangement and
the controlled external circuit. According to the types of external circuits, the pixelated ECDs can have
passive matrix, active matrix, and point-to-point driving modes . Based on three driving modes, we will
[87]
focus on the design strategies of pixel arrangement and subpixel device structure construction in flexible
and stretchable pixelated ECDs. Subsequently, we will elucidate the multifunctionality of these highly
integrated flexible ECD pixelated displays.

Firstly, the passive matrix-based ECDs are constructed by the row and column electrodes, where the
electrochromic subpixels are located in the intersection. With this matrix architecture, achieving a high
color contrast while mitigating cross-talk remains a primary objective . In current flexible and stretchable
[112]
ECDs, researchers have adopted the approaches for fabricating the polyelectrolyte pixels and using the V/3
addressing protocols to prevent the unwanted electrochromic phenomenon for inactive subpixels. In this
case, the flexible [Figure 10A] and stretchable [Figure 10B] PEDOT:PSS-based passive matrix-based
[113]
[114]
ECDs were successfully prepared with addressability and low cross-talk under mechanical conditions.
Secondly, the active matrix-based ECDs greatly solve the cross-talk issues because each electrochromic pixel
is combined with one transistor, which can turn off the unwanted current of the inactive subpixel [24,112,115] .
Kim et al. have successfully fabricated a 6 × 6 stretchable active matrix electrochromic array by introducing
an n-type field-effect transistor (FET) with the P3MT/PB ECD pixel using liquid metal interconnection on
the ITO-PET substrate, which showed a high-resolution display capability even under bending conditions
[Figure 10C] . To further improve the manufacturing feasibility of the display owing to the additional
[61]
transistor component, a fully screen-printed effective process was adopted to prepare the SWCNT thin film