Eliminating hysteresis effects in flexible organic light-emitting diodes

Abstract

Hysteresis effects in thin film transistors (TFTs) were reported to be a major factor of residual image for display application, but the role of hysteresis effects in organic light-emitting diodes (OLEDs) has rarely been demonstrated, especially that in flexible OLEDs. In this study we found that there are noticeable hysteresis effects in flexible OLEDs due to the migrated charges between the anode and hole transport layers (HTL) including the added charges from polyimide, which was characterized by the capacitance measurements. After that we discussed the approaches for eliminating hysteresis effects by tuning oxygen plasma ratio at anode to obtain a controlled charges concentration, thermal aging to influence the trapped charges at the anode and HTL, pulse width modulation (PWM) driving to release the successive charges accumulation, respectively. It was presented that samples with optimized oxygen treatment and PWM driving have extreme decrease (25.7% and 36.6%) of luminance gap induced by hysteresis effects, while those with thermal aging have no obvious influence. The research opens the possibility of considering the influence of hysteresis effects induced by charges movement on more self-luminous devices for their actual display application. • An effective and accurate technique using capacitance measurements to analyze the hysteresis effects of flexible OLEDs was creatively proposed. • The approach that anode modification can improve the residual image of OLEDs is firstly proposed systematically. • Samples with thermal aging and pulse width modulation (PWM) driving were experimented.