Study of stretchable organic light-emitting diodes with a stretchable platform based on low Young's modulus strain relief layers

Abstract

In this work, a stretchable organic light-emitting diode (OLED) has been realized. The stretchable platform,on which OLEDs are stacked, consists of rigid islands connected electrically and mechanically with serpentine shapedinterconnectors placed on a bilayer substrate based on a strain relief layer with low Young's modulus andan elastomeric substrate. When a floating, self-supporting serpentine-shaped interconnector is stretched, out-of-planetwisting tends to occur to reduce the strain applied to the interconnector. However, when interconnectorsattached to elastomeric substrates are stretched, the vertical movement is restricted, and the applied strain tendsto increase. To solve this problem, a strain relief layer having a very low Young's modulus is inserted betweenthe elastomeric substrate and the patterned plastic substrate. Due to the very low Young's modulus of the strainrelief layer, the serpentine interconnector has more freedom to move in a vertical direction, enabling the overallsystem to withstand a higher degree of stretching. Stretchable OLEDs are realized on this platform, and it wasconfirmed that stable operation is possible even when it is stretched to a significant degree. First-generationstretchable OLEDs are fabricated with a photo-patternable photoresist, SU-8, enabling stretchability is relativelylow due to the limitation of the material property. Therefore, polyimide (PI), a widely used plastic substrate inflexible OLED displays, is used to fabricate a more stable stretchable platform. To pattern this, commerciallyaccessible laser patterning was used, and to secure a surface at a level where OLEDs can be deposited, aphotoresist was coated to protect the surface during patterning. After this, poly(glycidyl acrylate-co-2-(dimethylamino)ethyl methacrylate (pGAD) was deposited to further increase the degree of planarization of thesurface, enabling the fabrication of an OLED that has very stable properties even on the patterned PI. In addition,a multi-layer thin-film encapsulation was applied to increase the environmental stability, leading to realization ofa passive-matrix stretchable OLED display that is operable in ambient air.