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.”
Conventional OLEDs are nonmagnetic, depending only on electrical fields to create excitons (electron-hole pairs), the recombination of which emits the photons that make an OLED glow. By mixing magnetic nanoparticles into the polymer matrix (at concentrations of less than one-tenth of 1 percent) Shen’s team found they could increase OLED efficiency by 27 percent. And by applying an external magnetic field to the doped OLEDs, an additional 5 percent was achieved, for a total increase in efficiency of 32 percent over conventional OLEDs, Shen said.
Light emission in solid-state LEDs occurs when high-energy injected electrons and holes recombine, dropping their energy levels and causing a single photon to be emitted to compensate. An LED with 100 percent efficiency would recombine every single injected electron and hole. In real devices, 100 percent efficiency is never achieved, but by confining them in a small region, designers can achieve the greatest efficiency possible, Shen said.
