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Page 20 of 28 Park et al. Soft Sci 2024;4:28 https://dx.doi.org/10.20517/ss.2024.22

Figure 9. (A) The conventional OLED module structure (left) and pol-less OLED module structure (right). Excluding the polarizer
necessitates the introduction of a black matrix on the color filter and a UV-blocking adhesive; (B) The UV-blocking adhesives were
prepared via visible-light-driven polymerization. With UV-block adhesive, the luminescence and voltage change were negligible after UV
[27]
exposure test . Reproduced with permission. Copyright © 2024 Springer Nature. OLED: Organic light-emitting diode; UV: ultraviolet.
periods, these adhesives should retain their properties without degradation, demonstrating aging resistance
and maintaining mechanical stability despite repeated flexible motions. Furthermore, aging resistance
against environmental conditions such as temperature, humidity, and UV can be accomplished by
appropriately formulating the monomers and additives that compose the adhesive, thereby creating a stable
adhesive under various environmental conditions.

In the future, flexible devices will need to operate reliably in extreme environments, be thinner yet more
efficient, and exhibit greater energy efficiency. Consequently, future adhesives must maintain consistent
viscoelastic properties over a wide temperature range, offer improved impact resistance despite low
thickness, and provide versatile functionalities. These functionalities may include UV blocking properties to
protect against everyday UV exposure and excellent heat dissipation properties to manage thermal loads.
Increasing energy efficiency can be approached from various perspectives. From the standpoint of using a
flexible device longer within a limited battery capacity, energy efficiency can be enhanced by minimizing the
drop-in brightness from the display to the user. This can be achieved by matching the refractive index of the
adhesive with adjacent layers and maximizing optical transmittance. Another perspective is to look at the
production aspect of adhesives. Energy efficiency in adhesive production can be increased by using faster
curing speeds and lower intensity light sources, which can be achieved by utilizing efficient photocatalysts
and initiators. Additionally, the development of flexible adhesives must support environmental
sustainability. There is significant demand for OCAs made from degradable, recyclable, or reusable eco-
friendly materials, aligning with global sustainability goals. This requires a comprehensive approach
encompassing the entire lifecycle of adhesives, from monomer synthesis and polymerization to post-use
disposal or recycling, ensuring they meet technical requirements while contributing to a sustainable future.

In summary, the requirements for adhesives used in flexible displays become increasingly complex as
display form factors evolve and functional demands grow. For foldable displays, particularly as the
technology matures in mobile phones, adhesives must reliably operate over a wider temperature range and
provide excellent UV blocking capabilities to expand their use to automotive devices. Conversely, adhesives
for rollable and stretchable displays are not yet fully commercialized, so their exact specifications remain
undetermined. However, these adhesives need superior viscoelastic properties and functionality to perform