Researchers from the Korea Advanced Institute of Science and Technology systematically achieved an external quantum efficiency of 50% or higher in OLED simulations that use only an external scattering medium instead of a macroscopic lens or complex internal structuring.
They used a combination of simulation and actual testing to obtain a maximum EQE of 56 % and a power efficiency of 221 lumens per watt (LPW). The simulation combined the radiation transport theory (RTT) for scattering films with the power-dissipation model for light-emission in multilayer thin films. The researchers explained that the equation-based nature of the radiation transport theory enables a global optimization that accounts for several variables for OLED stacks and scattering layers.
They pointed out that this proposed optimization method would require the use of highly horizontal dipole OLEDs. The researchers noted that in the simulation they were able to achieve the high EQE and power efficiency without a half-ball lens or a complex internal outcoupling scheme.
The group asserts that such high EQE and power efficiency was previous only available to compound semiconductor-based LEDs. The researchers also claim that their approach offers a practically viable path to ultrahigh efficiency. They point out that using their method is especially viable, given the simplicity of preparing scattering films. The researchers published the results of their simulations in Nature Communications.
Song, J., et al. Lensfree OLEDs with over 50% external quantum efficiency via external scattering and horizontally oriented emitters, Nature Communications, volume 9, Article number: 3207 (2018). DOI: 10.1038/s41467-018-05671-x