Recoverable degradation and internal field forming process accompanied by the orientation of dipoles in organic light emitting diodes

Recoverable degradation of a polyurethane (PU) derivative with large dipoles on the side chain was investigated. Spontaneous recovery and reverse bias-assisted recovery were observed. The observed spontaneous recovery and reverse bias-assisted recovery are explained by the formation of an internal electronic field due to the re-orientation of dipoles. The re-orientation of dipoles was evaluated by second harmonic generation measurement. The relatively large estimated value of χzyy(2), approximately 7×10−7 esu (2.93×10−10 m/V) at 10 V, indicates a high degree of orientation of dipoles, which generates a relatively large internal electronic field.