Organic mixed ionic–electronic conductors as active layers in light-emitting electrochemical cells: vibrational spectroscopic, microscopic and electronic characterization

We report on investigations of the morphological aspects of blend layers prepared from a blue-green light-emitting conjugated polymer (methyl-substituted ladder-type poly(p-phenylene), mLPPP), blended with either a crown ether, Dicyclohexano18crown6 (DCH18C6) or a high-molecular-weight poly(ethylene oxide) (HMWPEO), and a Li salt, lithium trifluoromethanesulfonate (LiCF3SO3, Litriflate, LiTf for short) as a solid state electrolyte as they were successfully applied as active layers in light-emitting electrochemical cells (LECs). The surface morphologies of the blends were investigated by atomic force microscopy (AFM) in Tapping mode© and the ion distribution with X-ray analysis by energy-dispersive X-ray spectrometry (EDXS) in the scanning electron microscope (SEM). The specific phase morphologies of the blends, the complexation of the ions and the ionic transport numbers were found to have tremendous influence on the performances of the corresponding LECs revealing either rectifying or symmetric optoelectronic characteristics in forward and reverse bias directions.