Fig. 4: The mechanical stability and optoelectrical characteristic of stretchable OLEDs under stretching operation.
a Resistance changes of a serpentine structure composed of PI layer, encapsulation layer, and Al layer, measured at the initial state during cyclic tests of equal biaxial stretching with the PA-ABL having open-area ratios (\({{{\eta }}}_{{{\rm{open}}}}\)) of 41% and 88%, respectively. b Current-voltage characteristics of a 3D pop-up structure fabricated using the PA-ABL with \({{{\eta }}}_{{{\rm{open}}}}\) = 88%. Measurement was done for equal biaxial strains of 0, 10%, 20%, 30%, and 40%. c The photographs of the proposed stretchable OLED devices with PA-ABL having \({{{\eta }}}_{{{\rm{open}}}}\) = 88% under the applied equal biaxial strain of 0, 25%, and 40%. d Current density (J)-luminance (L)-voltage (V) characteristics and (e) Current efficiency vs L of the stretchable OLEDs under various equal biaxial strains. f Normalized J, L, and current efficiency at a driving voltage of 6 V under cyclic stretch-release test for a biaxial strain of 40% (a.u., arbitrary unit). g (Left) Schematic diagram that illustrates convex deformation. (Right) Maximum strain of the elastomer surface versus radius of curvature ratio (r/R) obtained from FEA results. (Bottom) The photographs of working stretchable OLEDs under convex deformation with various r/R ratios. h System maximum strain (\({{{\varepsilon }}}_{{{\rm{sys}}}}^{{{\rm{max }}}}\)) and initial rigid-island area ratio (\({{{\gamma }}}_{{{\rm{I}}}{{\rm{0}}}}\)) of previously reported 2D rigid island platforms22,23,51,52,53,54,55,56,57,58,59 and the proposed stretchable OLEDs. The color map indicates the interconnector strain (\({{{\varepsilon }}}_{{{\rm{i}}}}\)) that is required to achieve (\({{{\gamma }}}_{{{\rm{I}}}{{\rm{0}}}}\), \({{{\varepsilon }}}_{{{\rm{sys}}}}^{{{\rm{max }}}}\)) in 2D rigid island platforms. The ‘star’ mark corresponds to (\({{{\gamma }}}_{{{\rm{I}}}{{\bf{0}}}}\) = 85% \({{{\varepsilon }}}_{{{\rm{sys}}}}^{{{\rm{max }}}}\) = 40%), achieved with the proposed 3D platform. If this level of performance had been achieved with the conventional 2D rigid island schemes, the required interconnector strain would have been as high as 512%.
