OakRidge National Laboratories claims that OLED efficiency can be increased by 30% by doping magnetic nanoparticles into OLEDs. Introducing a magnetic material into the OLED will control the brightness without the need for additional electrical contact.
According to Jian Shen, senior researcher at ORNL, "What we do is to enhance the luminescence efficiency of OLEDs by doping very low concentrations of magnetic nanoparticles into organic polymers. Doping allows us to control the density of OLEDs with magnetic fields. However, the traditional OLED density is regulated by the electric field, which requires electrical contact."
By mixing magnetic nanoparticles into the polymer array (less than one-thousandth of a percent), Shen's team found that they could increase the efficiency of OLEDs by 27%. By applying an external magnetic field to the doped OLED, the efficiency can be increased by another 5%, so that the efficiency is increased by a total of 32% compared with the conventional OLED.
When high energy injected electrons and holes recombine, light emission occurs in the solid LED, reducing their energy levels and causing a single photon to be emitted for compensation. LEDs with 100% efficiency recombine each injected electron and hole. In practical devices, they never achieve 100% efficiency, but by limiting them to small areas, design engineers can achieve maximum efficiency as much as possible, Shen said.
When electrons and holes are paired, they are called excitons before they are recombined. The magnetic spins of each part of the excitons are random, resulting in their efficiency in recombination being variable. To improve the efficiency of the recombination, Shen's team mixed magnetic nanoparticles made of cobalt and iron (CoFe) with polymers of organic OLEDs. Due to the presence of magnetic nanoparticles, a larger number of excitons with reverse spins are stacked, called zero-spin excitons. Reverse polarity charge carriers are more likely to recombine, thus making magnetically doped OLEDs more efficient, Shen said.
Shen introduced, "By increasing the proportion of so-called zero-spin excitons in the total excitons, the presence of CoFe magnetic nanoparticles increases the efficiency of electroluminescence and its fluorescence."
Next, Shen's team will experiment with different doping levels and various methods of mixing magnetic nanoparticles with polymers to achieve ultra-consistent concentrations, hoping to further increase efficiency.
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