Research On New Organic Light-emitting Diodes With Low Operating Voltage

Because of its unique advantages,OLEDs are known as the third generation display technology and have a wide range of applications in the field of lighting.The luminescence performance of OLED devices is closely related to the driving voltage.Low driving voltage can effectively reduce the unnecessary Joule heat generated by the device and improve the integrated performance of the device,thus ensuring the stability of the luminous device.Reducing the operating voltage and prolonging the lifetime of blue-light OLED devices has always been a bottleneck in OLED research.In this paper,we fabricated two systems blue electroluminescence devices based on representative fluorescent and phosphorescent materials.By optimizing device structure and the thickness of each functional layer,and analyzing the performance parameters of the obtained devices,an effective method in fabricating low-voltage and high-efficiency organic light-emitting devices was demonstrated.First of all,we choose the high efficiency blue fluorescence material Bepp2 as the luminescent material.According to its energy level and luminescence characteristics,we select the matching host materials Tc Ta and 26 DCz PPy.Introducing a high performance hole injection material HAT-CN into the anode interface can reduce the hole injection barrier between the anode and the hole transport layer,and improve the hole injection and transmission ability.The carrier transmission and distribution under different device structures are further studied by analyzing the light-emitting characteristics and electroluminescence spectra.The experimental results demonstrated that performances of Bepp2 doped Tc Ta single-EML device were higher than those of Bepp2 doped 26 DCz PPy single-EML device.By optimizing the doping concentration of the luminescent materials and the thickness of the functional layer,the carrier accumulation at the interface can be effectively reduced and the device color purity can be improved.The optimal turn-on voltage of double-layer devices based on Bepp2 luminescent materials is 2.9 V.Subsequently,we choose FIrpic as the luminescent material.On the basis of the blue fluorescent material system,we replaced the host materials and luminescent materials to fabricate high-performance blue phosphorescent devices.Among them,m CP has a high triplet energy level(ET=2.9 e V)and good hole transport characteristics as the host material of blue electrophosphorescence devices.The bipolar host material Cz Si was chosen as host material for the double-layer devices.By optimizing the doping concentration of luminescent material and the thickness of light emitting layer,the performance of the device were significantly improved.The single-layer device structure was chosen to ensure the high efficiency of the device while further reducing the operating voltage of the device.Compared with the two hosts devices with Cz Si,the single-m CP light-emitting layer device reduces the thickness of the device and the driving voltage;moreover,the device performance has been improved,indicating that the carrier recombination region is mainly in the m CP light-emitting layer,which can better balance the carrier distribution and improve the device performance.Finally,the maximum brightness,current efficiency and power efficiency of high performance devices are 37070 cd/m2,43.08 cd/A and 50.13 lm/W respectively,and the starting voltage is only 2.7V.