Degradation study in flexible substrate organic light-emitting diodes

Indium tin oxide (ITO) coated polycarbonate (PC) multilayer flexible substrates have been subjected to different cycles of bending. Atomic force microscopy (AFM) results on bent ITO surfaces show that bending results in much rougher ITO surfaces. The Ca degradation test shows that the ITO cracks are perpendicular to the flexing direction and that barrier performance deteriorated after bending. When an organic light emitting device is fabricated on the bent substrate, electrical and optical performance decrease. This can be attributed to moisture and oxygen permeated through deteriorated substrate and barrier degraded polymer and oxidized cathode materials. However, optical microscopy observation found that the dark spots have less relationship with the size and position of the cracks on oxide film. Instead to a great extent, they are directly related to the ITO surface spikes. The results further prove that the dark spot is due to electrical stress generated by intense local current at sharp anode and cathode points, which degrade the polymer causing the formation of the dark center. PACS 78.66.Qn; 82.35.Cd; 62.60.Mk