Effects of molecular ordering on circularly polarized emission from a twisted mesogenic conjugated polymer

Abstract

Circularly polarized (CP) photoluminescence and electroluminescence (EL) generated from the emitting layer can improve the light efficiency of a commercialized organic light-emitting display. High CP emission is generated from the twisted configuration of a mesogenic conjugated polymer. However, the effect of the material and device parameters on the degree of CP emission, defined by the dissymmetry g factor, has not yet been fully studied. Through carefully investigating various parameters under various experimental conditions, it was found that the degree of CP emission can be expressed as the quadratic equation of the order parameter (S). Furthermore, a considerable degree of CP emission (g = 0.37 in the EL process) can be measured even when the order parameter was zero. Such results imply that the twisted stacks even at a random orientation are predominant rather than the formation of a uniform orientation to generate CP light. Also, the anti-reflection condition, required in conventional organic light-emitting diodes to eliminate the reflection of ambient light from a metal cathode, is still maintained since there is no retardation in the ambient light for S = 0 while emitting CPEL, which leads to an enhancement of luminance efficiency by about 18.5%. It is expected that these results, discussed herein, pave the way toward understanding the mechanism of CP emission and enhancing the performance of the CP emission.