Boosting quantum efficiency of single layer organic light emitting device by doping CoFe magnetic nanoparticles.*

The effects of doping magnetic CoFe nanoparticles on electroluminance (EL) efficiency vs. current density, and current density vs. applied voltage for single layer organic light emitting devices (OLEDs) have been investigated. The electron trap densities increased with the increase of CoFe dopants, resulting in a high trap-filled limit (TFL) threshold voltage and significant enhancement EL efficiency ($\sim $27{\%}). The EL efficiencies were further improved ($\sim $5-7{\%}) by applied magnetic field. These improvements could be attributed to the enhancements of the ratios of the formation of excitons, and singlets to triplets, respectively and simultaneously. A maximum 32{\%} enhancement combing the two effects in EL efficiency has been achieved.