Optical Design that Increases Light-Extraction Efficiencies of Organic Light-Emitting Devices through Finite-Difference-Time-Domain Method

The efficiency of light extraction in organic light-emitting devices is insufficient for practical use. This low efficiency is mainly attributed to the refractive index of the light-emitting layer. As the source of an organic light-emitting device is the sum of the point sources, and the wavelength of the emitted light and the scale of the optical structure are comparable, the near-field from the source plays an important role in determining the efficiency with which light is extracted in organic light-emitting devices. Finite-difference time-domain (FDTD) calculations were used to simulate conditions that could not be illustrated with ray optics. We found that the spherical Poynting vector of a point source becomes normal to the high index-ratio interface situated in the near field of the source, and this transformation of the Poynting vector results in the light-extraction efficiency being increased.