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Keum et al. Soft Sci 2024;4:34 https://dx.doi.org/10.20517/ss.2024.26 Page 9 of 32

Figure 5. Various stretchable electrodes and interconnects for stretchable LED displays. (A) Interconnection of micro-LEDs using printed
PEDOT:PSS and demonstration of a 7-segment display unit [39] . Copyright 2019, Wiley-VCH; (B) (i) Optical images of a porous
GHC/PDMS composite. (ii) Operation images of a stretchable display constructed using GHC [40] . Copyright 2018, Wiley-VCH; (C) (i)
Schematic illustration of PSS attached EGaIn particles. (ii) Operation of a LED display with EGaIn/PSS interconnects [42] . Copyright 2023,
Elsevier; (D) Conceptual illustration of 2D-contact stretchable electrodes and a 5 × 5 passive matrix ISOLED [44] . Copyright 2022, Wiley-
VCH. LED: Light-emitting diode; PEDOT:PSS: poly(3,4-ethylenedioxythiophene) polystyrene sulfonate; GHC: graphene honeycomb;
PDMS: polydimethylsiloxane; 2D: two-dimensional.

structured PSS attached EGaIn thin-film on various substrates through the photolithography process and
used as an interconnect to implement multifunctional soft electronic devices such as 6-inch stretchable LED
displays [Figure 5C(ii)]. As another example, Zhou et al. reported graphene-based 2D-contact stretchable
electrodes (TCSEs) that incorporate a layer of graphene on top of embedded AgNWs networks in the
styrene-ethylene-butadiene-styrene (SEBS) elastomer matrix [Figure 5D]. The researchers improved the
[44]
mechanical stability and charge injection by using the mixture of 2D structure graphene layer and the 1D
structure AgNWs. The assessment of low work function due to the induced interfacial dipole is explained as
the underlying mechanism. Based on the fabricated electrode, an intrinsically stretchable organic LED
(OLED) display was demonstrated to have a current efficiency of 20.3 cd·A . Furthermore, by utilizing the
-1
TCSEs, they successfully implemented a stretchable 3-inch 5 × 5 passive matrix OLED array [Figure 5D].

Mechanical pattern design or microstructure engineering
This section introduces several approaches to improve the durability during stretching by optimizing the
structural design. Generally, when applying mechanically brittle semiconductors or conducting materials to
stretchable devices, designing the macro-scale (extrinsically stretchable components) and the micro-scale
(intrinsically stretchable materials) can be a critical component including geometrical design engineering
such as wrinkled structures (pre-stretching approaches), island-bridge structures, microstructures, and
stretchable platforms . Zhu et al. designed both mechanically interlocking structures and chemical
[15]
adhesive polymers to assemble individual soft devices onto soft patternable circuits toward multifunctional