Optically detected magnetic resonance studies of pi-conjugated polymer-based light-emitting diodes

摘要

Abstract: The X-band photoluminescence (PL)-, electroluminescence (EL)-, conductivity ($sigma@)-, and photoconductivity ($sigma$-ph$/)-detected magnetic resonance of poly(p-phenylenevinylene) (PPV) and poly(p-phenyleneacetylene) (PPA)-based LEDs is described and discussed. A strong narrow PL-enhancing and EL-quenching resonance is observed at g $APEQ 2.0023 in all cases. However, while the $sigma@- and $sigma$-ph$/-detected resonances are also quenching in the PPV- based diodes, the $sigma@-detected resonance of the PPA-based diodes is enhancing. The g-values and lineshapes of all of the resonances are identical in each type of diode, and they are attributed to polaron-polaron fusion to singlet excitons or bipolarons. The implications of this picture to the issues of polaron and bipolaron mobility in these diodes and a potential upper limit of their efficiency is discussed. In addition to the narrow resonance, half- field PL-, EL-, $sigma@- and $sigma$-ph$/-detected resonances due to the $Delta@m$-s$/ $EQ 2 transitions of triplet excitons are also observed. These resonances are believed to result from singlet exciton generation via triplet- triplet fusion.!20