Study On Light Extraction Efficiency Of Organic Light-emitting Diode Based On Grating Structure

Organic light emitting diode(OLED)has the characteristics of environmental protection,low power consumption,wide color gamut and self-luminous.It is widely used in the field of display and lighting.At present,the internal quantum efficiency of OLED can almost reach 100%.However,due to the characteristics of OLED multilayer structure,due to the optical effects such as total reflection and waveguide mode between each layer of media,some light emitted by the device is bound inside the device,resulting in the reduction of external quantum efficiency of OLED Low.In order to improve the luminous efficiency of OLED and further improve the luminous performance of OLED,it is an effective way to improve the light extraction efficiency of OLED by optical means.Considering the influence of dipole light source orientation and light source position,the luminous efficiency of single-layer and double-layer OLEDs with different grating structures is studied by time domain difference method,and the mechanism of improving luminous efficiency is explored.The main research is as follows:Firstly,the extraction efficiency of monochromatic light from single-layer planar OLED is studied.By optimizing the thickness of ITO layer and organic layer of single-layer planar OLED,it is obtained that the extraction efficiency of singlelayer planar structure after optimization is 1.55 times higher than that before optimization,which reveals the influence of the optical length of organic layer and ITO layer on the electric field distribution and far-field power.Secondly,the extraction efficiency of green light in single-layer OLED with grating structure is studied.Right triangle grating,isosceles triangle grating,isosceles trapezoidal grating,rectangular grating and semicircular grating are constructed in the ITO layer of single-layer planar OLED respectively.The relative extraction efficiency of various grating OLEDs and the optimal structural parameters of the grating are calculated.The best way to improve the extraction efficiency of OLED is the semicircular grating with a duty cycle of 0.4 and a radius of 600 nm.The light extraction efficiency is 1.2 times than that of the optimized planar OLED.The reasons for the improvement of luminous efficiency are explored through the auxiliary analysis of geometric optics.Thirdly,the effect of high refractive index materials on extraction efficiency was studied.The grating structure is constructed with high refractive index materials.Through the optimization of the grating refractive index and structure,the optimal structure is a semicircular grating structure OLED with refractive index of 2.6,duty cycle of 0.5 and radius of 840 nm.Its extraction efficiency is 1.47 times than that of the optimized single-layer planar OLED.A semicircular glass grating is constructed on the glass substrate layer of single-layer OLED.When the duty cycle of the glass grating is 0.4 and the radius is 880 nm,the light extraction efficiency of OLED is 1.1times higher than that of the grating structure without glass grating.Finally,the extraction efficiency of three primary colors in double-layer OLED is studied.For the incident light of 480 nm,550nm and 680 nm,the best double-layer OLED structure is calculated respectively,and its illumination characteristics are evaluated by CIE chromatogram.Among them,the semicircular OLED can emit pure white light,which is the most suitable for illumination.This study has certain theoretical significance for the structural design of OLED.