Organic electroluminescent (EL) devices using molecularly dispersed poly(N-vinylcarbazole) (PVCz) exhibit an irreversible transition phenomenon with a simultaneous and remarkable improvement in carrier injection at high bias voltage by doping with ammonium salt. The device structure used in this study was an indium tin oxide anode/PVCz:2,5-bis(1-naphtyl)-l,3,4-ox adiazole:coumarin 6:tetra-n-butylammonium tetrafluoroborate/metal cathode. The altered devices require significantly lower driving voltage and exhibit higher EL intensity compared with undoped devices. Furthermore, the EL intensity-voltage characteristics of the altered devices are independent of the work function of the cathodes.