Study Of White Organic Light Emitting Device Based On Ultrathin Emitting Layer

Organic light-emitting devices?OLEDs?have drawn substantial attention owing to their outstanding merits,such as high efficiency,bright luminance,low driving voltage and possible implementation on flexible substrates.Specially,white OLEDs?WOLEDs?is hailed as the next-generation of solid-state lighting devices and display technology because of its application value.However,Consumers can't afford the expensive price of WOLED products,mainly due to high manufacturing costs WOLED.In this paper,a non-doped WOLED is fabricated,in which the blue light-emitting layer adopts the Thermally Activated Delayed Fluorescence?TADF?material,the red ultra-thin emitting layer and the green ultra-thin emitting layer are respectively red phosphorescent material and green phosphorescent material.With such undoped structures,manufacturing costs are reduced by simplifying manufacturing processes.The details are as follows.?1?A blue light device using pure blue TADF material DMAC-DPS as the emitting layer was prepared.It was verified that pure DMAC-DPS can be used as a blue emitting layer of undoped WOLED device to contribute blue light component to white light.Based on this,three different emitting layer structures of WOLEDs were fabricated by inserting a red ultrathin phosphorescent emitting layer and a green ultrathin phosphorescent emitting layer.The device with blue/red/blue/green emitting layer structure exhibited optimum color stability,wherein a blue emitting layer between the two ultrathin emitting layers also functions as an exciton adjusting layer.Via adjusting the thickness of the exciton adjusting layer,it is found that the performance of these devices increased first and then decreased with increasing thickness.The device with the 4 nm thickness of the exciton adjusting layer emitted white light,and its maximum luminance,maximum current efficiency,maximum power efficiency and maximum external quantum efficiency are 24775 cd/m²,12.14 cd/A,8.94 lm/W,8.32%,respectively,and the CIE coordinates are?0.32,0.33?at a bias of 7V.?2?With the thickness variation of the red ultrathin emitting layer Ir?h-piq?₃ and the red ultrathin emitting layer Ir?h-piq?₃,it was confirmed that enhancing energy transfer of DMAC-DPS to Ir?h-piq?₃ and Ir?ppy?₃ improved the color stability of the device.The best performance is acquired when the thickness of Ir?h-piq?₃ and the thickness of Ir?ppy?₃ was appropriate,the maximum luminance was 26379 cd/m²,the maximum current efficiency and maximum power efficiency is 22.62 cd/A and 14.54 lm/W,respectively,and the maximum external quantum efficiency reached 15.18%.The device exhibitd the best color stability with optimizing the thickness of Ir?h-piq?₃,with the luminance increases from 100 cd/m² to 5000 cd/m²,the color coordinate drift was only?0.01,0.05?.In conclusion,non-doped WOLED was fabricated,the blue emitting layer also acts as an exciton adjusting layer adopted pure blue TADF material,which can regulate the exciton distribution at the red ultra-thin emitting layer and the green ultra-thin emitting layer.This structure allows the Dexter energy transfer and F?rster energy transfer to achieve dynamically balanced.This work may generate a wide range of interest in the fabtrcation of high color stability and high efficiency undoped WOLED.