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Keum et al. Soft Sci 2024;4:34 https://dx.doi.org/10.20517/ss.2024.26 Page 25 of 32

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process allows the fabrication of devices in almost endless ways . Transfer printing, a similar assembly
technique, utilizes a soft polymer stamp to transfer functional elements fabricated on rigid substrates onto
other stretchable substrates. This approach is promising for combining and integrating multi-scale and
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diverse types of organic and inorganic materials as needed . The transfer printing technique can handle a
large number of components, making it particularly valuable for developing advanced display systems, such
as stretchable micro-LEDs, through the heterogeneous integration of inorganic materials with soft
elastomers . Lastly, by utilizing a photoresist layer, it is possible to achieve precise patterning at the
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microscale, enabling the fabrication of stretchable electrodes and interconnects, which can serve as the
foundation for stretchable TFTs and functional circuits. This simple and efficient process involves
patterning interconnect materials, such as LMs, by selectively removing the photoresist layer to form robust
liquid patterns, similar to the photolithography and lift-off process used for solid metal thin films [38,81] . This
novel approach plays a significant role in realizing highly integrated circuits and effective stretchable
platforms that require high-resolution and precise patterning of stretchable materials.

CONCLUSION AND OUTLOOK
In summary, this review explored recent research trends in functional materials and structural designs for
stretchable displays. Over the past few years, stretchable display technology has seen significant progress in
various areas of stretchable LED devices, driven by material and structural innovations in electrodes,
interconnects, luminescent materials, and semiconductors [Figure 14]. However, challenges remain in terms
of materials and manufacturing processing in stretchable electronics fields. To provide stretchability in
displays, it is crucial to simultaneously achieve high optical clarity, electrical conductivity, high carrier
mobility, and mechanical robustness. Stretchable displays represent a significant departure from traditional
display technologies by enabling free-form shape changes. However, this flexibility introduces substantial
technical challenges. Despite various morphological and structural engineering strategies demonstrating the
feasibility of stretchable displays, they are still considered as a future-oriented technology due to numerous
limitations. Therefore, the current research in stretchable display technology should focus on the following
key aspects:

1. Development of stretchable substrates with zero or negative Poisson’s ratio: To mitigate image distortion
during stretching, it is crucial to enhance the fill factor of the active area while applying substrates with zero
or negative Poisson’s ratio. Achieving this will likely require the incorporation of innovative and unique
materials in the substrate form factor, or the utilization of diverse structural approaches, including meta-
structures or 3D-shape structures.

2. Advancement in fabrication techniques for stretchable electronic components: In the fabrication of
stretchable electrodes, interconnects, semiconductors, and emissive layers, improving yield and scalability is
essential. To facilitate large-area and mass production, various printing processes should be explored. These
techniques must ensure high yield and productivity to make stretchable displays commercially viable.

In response to these requirements, diverse in-depth research has been performed by numerous researchers
in the areas of electrode/interconnect design, emissive layers, and TFTs for integrated circuits. Also, various
material engineering including organic/inorganic-based materials, low-dimensional nanomaterials, and
stretchable substrates has been performed to apply in the stretchable displays. These findings have spurred
attempts to apply the technology to promising fields such as skin-like displays that integrate sensors and
displays for the next-generation electronic skin applications, neuromorphic systems mimicking the
biological functions, and soft robotics. Despite the remarkable advancements in stretchable display
technology, challenges remain, including environmental stability, relatively low resolution and image