Study On Blue OLED With Both High Chromatic Efficiency And Low Turn-on Voltage

Organic light-emitting diodes(OLEDs)are attracting more and more interests due to their excellent advantages,such as self-luminescence,high efficiency,wide viewing angle,high color saturation,quick response,and sample manufacturing process.Among the various colors of OLED devices,red,green,and blue OLEDs,which are the three primary colors in display,are more worth studying.At present,red and green OLED devices are around the corner of commercialization in terms of stability and efficiency.When it comes to blue OLEDs,much effort should be further devoted to solve problems,such as stronger efficiency roll-off than red and green OLEDs,poor stability,and difficulties in developing suitable function materials to match blue emitting materials that has wide band gap.Focused on deep blue OLEDs,in the desire of low drive voltage,high stability,and high color efficiency,this thesis are organized with the following aspects:(1)The guest material TPIE with EL peak around 460 nm was doped into the DMPPP host material to get blue emission.Charge carrier balance was achieved by adjusting the thickness of hole transport layer(HTL).The p-doping of HTL reduced the turn-on voltage of the devices,which contribute to a lower power consumption.The addition of exciton blocking layer further improved the stability and reduced the roll-off of the devices.(2)By introducing the optical interference microcavity structure into the deep blue OLED devices to get optimal optical path length,the monochromaticity and color efficiency were greatly improved.The CIE coordinates shifted from(0.17,0.16)to(0.14,0.05),and the chromatic efficiency was improved by 2 times.(3)The reflectivity of the translucent cathode in the emitting OLED devices has remarkable influences on the emission spectra.In this thesis,the effects of reflectivity of cathode on the controlling of emission spectra of top emitting device were verified by simulation and devices preparation.(4)The phenomenon that the spectra of the top emitting devices were blue-shifted with the increasing of observation angle,as well as the influences of cathode capping layer(CPL)on the performance of devices were simulated and explained.