With recent developments in the field of wearable and biomedical electronics, fabrication of stretchable organic light-emitting diodes (SOLEDs) has received great attention. Most of the reported SOLEDs were analyzed for uniaxial (x or y-axis) tensile strains only. However, due to wide angular moments of human body organs, ‘wearable electronics’ are expected to perform under multi-axial tensile as well as compression strains. The strain ratio (SR) of the demonstrated devices has also reached a maximum value of 0.5 and needs improvement.
This work presents the fabrication of wavy organic light-emitting diode (WOLED), which is capable of performing under multi-axial tensile and compression strains with higher strain ratios. The OLED device was first fabricated using conventional methods on a silicon substrate and then the device was peeled off and transferred to a thermally pre-strained PDMS, using kinetic transfer method. The pre-strain temperature was 150 °C and it induced a thermal expansion of about 1.3%. Random two-dimensional (2D) wavy buckles were formed by cooling down the PDMS substrate due to the difference in thermal coefficients. Instead of a universally used mechanical pre-strain method, we could make a device with multiaxial buckles through thermal pre-strain. The WOLED device was analyzed at 1.5% and 3% tensile and compression strains with a SR of 1.16 and 2.33, respectively. The device demonstrated good performance in the green light region up to 1.5% and showed comparable results even at 3% tensile and compression strains. A slight blue-shift in the electroluminescence analysis demonstrated that a various wavelength luminescence can be obtained by just altering the buckle size which can be controlled by the amount of pre-strain. Finite element simulation analysis was conducted, which provided valuable information about the presence of neutral plane in the device and a coherence between simulation and experimental results was observed.
The fabricated WOLED device presented a strong capability of performing under multi-axial tensile and compression strains with large strain ratios. The facile fabrication by conventional methods introduced in this work has a high potential to find its way to the next generation fields of stretchable/wearable electronics, electronic newspapers and curvilinear/expandable displays.