OPTICALLY DETECTED MAGNETIC-RESONANCE STUDY OF EFFICIENT 2-LAYER CONJUGATED POLYMER LIGHT-EMITTING-DIODES

We report the results of electroluminescence-detected magnetic resonan ce (ELDMR) measurements on efficient two-layer polymer light-emitting diodes (LED's) comprising a hole-transporting layer of poly(p-phenylen evinylene) (PPV) and an emissive layer of a cyano-substituted PPV deri vative (CN-PPV). By comparing the ELDMR and conductivity-detected magn etic resonance (CDMR) results with photoluminescence-detected magnetic resonance on films of the polymers making up the LED, we are able to identify the components of the ELDMR and CDMR signals with processes o ccurring in either the PPV or the CN-PPV layers. We are, thus, able to establish the presence of triplet excitons in the CN-PPV layer. We al so reveal the importance of bipolaron formation in the PPV layer, and discuss the assignment of the other ELDMR and CDMR features.