Realizing Stretchable OLEDs: A Hybrid Platform Based on Rigid Island Arrays on a Stress‐Relieving Bilayer Structure

Abstract

Optoelectronic devices that are stretchable can revolutionize various fields by enabling the functionalities that are not accessible from conventional rigid platforms. In this respect, many efforts are made to realize stretchable organic light‐emitting diodes (OLEDs) for their compatibility with various deformable substrates. Two representative examples of such efforts include a method based on intrinsically stretchable materials and a method to attach ultrathin OLEDs on a prestrained elastomer substrate. However, both of those methods have limitations either in material availability for high performance or in optical clarity. Here a hybrid platform is proposed for stretchable OLEDs free from such limitations. The proposed platform is composed of an array of rigid islands connected by serpentine‐shaped interconnectors formed on a bilayer elastomer substrate in which the top layer has an ultralow Young's modulus of ≈0.9 kPa, greatly relieving the rigid islands and interconnectors of the mechanical stress applied to them when stretched. With the proposed platform, stretchable OLEDs are demonstrated that can be repeatedly stretched by 140% and are based on thermally evaporable materials well established for fabrication of high‐performance OLEDs.

Materials and design strategies for stretchable electroluminescent devices

“…Through structural engineering, stretchable LED arrays using rigid EL devices can be developed. [74][75][76][77] Although each lightemitting unit is not flexible, the entire array can be stretched using submillimeter-size LEDs and stretchable interconnection. During mechanical deformation, the interconnects are deformed instead of LEDs and release the stress applied to the device, avoiding mechanical failures.…”

Structures and Materials in Stretchable Electroluminescent Devices

“…The luminance at a constant 6.5 V decreased by 19% after 1000 repeated stretch-release cycles between 0 and 20% strain. Kim et al [38] took a different approach for stress relief where a thick ultrasoft silicone elastomer layer (Silbione; Young's modulus ≈ 0.9 kPa) was inserted in between PDMS substrate and SU-8 layer (Figure 3h). Their experiment results showed that the maximum stretchability of the interconnects was increased from 170% to 350% as the modulus of Silbione was decreased from >10 to 0.9 ± 0.02 kPa.…”

“…i) Photograph of stretchable OLED where 140% maximum stretchability for the interconnects was demonstrated. Reproduced with permission [38]. Copyright 2020, Wiley-VCH.…”

22‐4: Invited Paper: OLEDs for Wearables: From Form Factor Engineering to Healthcare Applications

“…SU-8, polyimides, etc.) [2]. The elastomer substrates basically limit the overall degree of stretching capability and provide straightforward handling.…”

“…Therefore, it is not necessarily trivial to realize working organic devices with such various form factors. In this work, we will first address key issues in forming deformable organic lightemitting diodes (OLEDs) with case studies done for ultrathin and stretchable OLEDs [1,2]. In addition, we present OLEDbased wearable healthcare applications such as OLED-based pulse oximetry sensors [3][4][5].…”