Enhancement of quantum efficiency of organic light emitting devices by doping magnetic nanoparticles

Magnetic nanoparticles of CoFe are used as dopants to enhance the quantum efficiency of electroluminance in a single layer organic light emitting device (OLED). The enhancement of quantum efficiency increases with both increasing density of CoFe nanoparticles and external magnetic field. For a given OLED with $0.1wt%$ doping, the enhancement of the quantum efficiency reaches $∼27%$ and $∼32%$ without and with a magnetic field, respectively. The origin of these improvements could be attributed to the simultaneous increases of the portion of excitons among total charge carriers and the fraction of singlets among the total excitons