Oak Ridge National Laboratory (ORNL) claims it can make OLEDs 30 percent more efficient by doping them with magnetic nanoparticles. As a bonus, the introduction of magnetism into the OLED material enables brightness to be controlled without the addition of electrical contacts.
"What we did was to enhance the lighting efficiency of an OLED by doping the organic polymers with a very low concentration of magnetic nanoparticles," said ORNL senior researcher Jian Shen. "Doping also allows us to control the OLED-s intensity with a magnetic field, whereas conventional OLED intensity is tuned by an electric field, which needs [electrical] contacts."
When electrons and holes pair up, but before they recombine, they are called excitons. Ordinarily, the magnetic spin of each member of an exciton is random, accounting for their variable efficiency in recombining. To increase the efficiency of recombination, Shen's group doped the organic LED's polymer with nanoparticles made magnetic with cobalt and iron (CoFe). In the presence of the magnetic nanoparticles, a larger number of excitons with opposite spins accumulate, called singlet excitons. Oppositely polarized charge carriers are much more likely to recombine, accounting for the higher efficiency of the magnetically doped OLEDs, Shen said.
