Elucidating the influences of mechanical bending on charge transport at the interfaces of organic light-emitting diodes

In this study, we investigated the effect of mechanical bending on the performance of flexible organic light-emitting diodes (f-OLEDs). External bending was applied to induce tensile stress in the device. The current-voltage-luminescence (J-V-L) characteristics of the f-OLED were measured before, during, and after bending. The variation in the f-OLED performance was explained in terms of the changes in the injection barrier measured using ultraviolet photoelectron spectroscopy (UPS). Charge carrier transport was investigated using X-ray photoelectron spectroscopy (XPS). Impedance spectroscopy (IS) was used to analyze the dynamics of the charge carriers. The variations in photoluminescence (PL) peak intensity and position were used to investigate the effects of the inter- and intra-chain distances in the active layer of the f-OLED on the carrier mobility. Based on our analysis, we found that the degradation of the f-OLED after mechanical bending was induced by an increase in the number of charges accumulated at the interface between the emission layer and the electron transfer layer in the f-OLED.