The Preparation And Research On White Organic Light-emitting Diodes (WOLED)

Organic light-emitting diodes （OLEDs） as a new type of flat panel displays,owing to their excellent performance of low driving voltage、 high luminousefficiency、wide viewing angle、light weight and so on, has been developing rapidly inrecent years. White organic light-emitting diodes （WOLEDs） can be used insolid-state lighting and the backlight of LCD; exhibiting broad prospects in thesefields. It has become a hot research direction at present.According to the principle of white light combination, highly efficient blueemission is the key for preparing the WOLEDs. Firstly, the blue devices with4,4’-bis（2,2’-diphenylvinyl）-1,1’-biphenyl （DPVBi） as a blue emitter were fabricatedand studied. Thicknesses of the hole buffer layer MoO₃and the blue emitting layerDPVBi were optimized. We find out that the device with MoO₃as the hole bufferlayer has better performance than that with CuPc as a hole buffer layer. This may beattributed to formation of ohmic contact between ITO （indium tin oxide） anode andorganics by insertion of MoO₃. But the thicker MoO₃buffer layer will lead to thedevice’s EL （electroluminescence） spectrum red shift. Through the analysis of data,the best thickness of MoO₃layer is0.5nm. Fixing the MoO₃-thickness of0.5nm; theinfluence of emitting layer （EML） thickness on the device performance wasinvestigated by tuning the thickness of DPVBi layer. The device with40-nm-thickDPVBi layer shows best performance with turn-on voltage of only3.3V. Themaximum current efficiency reaches as high as4.1cd/A when current density is0.02mA/cm², maximum luminance of10890cd/m²is obtained at a current density of700mA/cm². In the large current density range, Commission Internationale de l’ Eclairage（CIE） co-ordinates are around （0.15,0.15）.Rubrene （5,6,11,12,-tetraphenylnaphthacene） has been used as the yellow emitter,and introduced in the blue emitting layer by using a ultra-thin technique to get whitelight. The effect of the position of the ultra-thin Rubrene layer on the performance of thedevices has been studied. We find out that the emitting color of the device changes withthe position of rubrene layer. the device’s color is white as the Rubrene layer is6nmaway from the hole transport layer NPB/DPVBi interface.The CommissionInternationale de l’ Eclairage （CIE） co-ordinates are （0.33,0.33）, the maximum currentefficiency is6.7cd/A （@0.2mA/cm²）, the maximum luminance of13266cd/m²isobtained at a current density of500mA/cm².