Preparation Of New Type And High Performance Organic Light-Emitting Devices Based On Small Molecular Materials

Organic electroluminescent device(OLED)is a kind of high brightness,wide viewing angles,thoroughly cured electroluminescent(EL)devices,and have incomparable advantages compared with other display device.Though OLED has made significant progress and has been commercialized,but still there are some important problems,for example,life problem,efficiency problem,colour purity problem,large size problem and other technology problems.To realize complete practical utilization and marketization of OLED,there are a lot of important theoretical and technical problems need to solve.In this paper “preparation of new-type and high performance organic light-emitting devices based on small molecular materials”,through exploring the organic EL mechanism,designing a new device structure,and optimizing the preparation technology,we improve the efficiency of electroluminescence,reduce the working voltage,mitigate the efficiency decreasing,and thus improve the device performance.(1)First,we separately investigated the dependence of electron injection and transport processes on the doping concentration by comparing the current density-voltage(J-V)characteristics of a series of electron-only devices with Alq3 doped into NPB as transport layer.With the help of EL spectra,recombination centers of 0.2% and 0.6% doped EL devices were probed to shift toward cathode and anode,respectively.These results suggest that electron hopping between among Alq3 molecules becomes the dominant electron transport mechanism when the doping concentration is higher than 0.6%.(2)Second,we designed and fabricated a series of electroluminescent(EL)devices with single-or double-light-emitting layer(s)(EML)to further improve the EL performances of green iridium complex(tfmppy)2Ir(tpip).P-type material TcTa and bipolar material 26 DCzPPy were chosen as host materials of EML1 and EML2,respectively.Compared with single-EML device,this design strategy demonstrated to be efficient in improving EL efficiency,broadening recombination zone as well as delaying the roll-off of EL efficiency.Finally,high performance green EL device with the structure of ITO/MoO3(3 nm)/TAPC(50 nm)/(tfmppy)2Ir(tpip)(6 wt%):TcTa(5 nm)/(tfmppy)2Ir(tpip)(6 wt%):26DCzPPy(11 nm)/TmPyPB(45 nm)/LiF(1 nm)/Al(120 nm)was fabricated.The maximum brightness,current efficiency,power efficiency and external quantum efficiency(EQE)of this device was 113610 cd/m2,112.30 cd/A,97.95 lm/W and 29.4%,respectively.Even at the certain brightness of 1000 cd/m2,current efficiency as high as 107.6 cd/A(EQE=28.1%)can be retained by the same device.At the current density of 10 mA/cm2,this device still displayed the Commission Internationale de l'Eclairage coordinates of(0.294,0.646).(3)Third,we attempt to improve the EL performances of red light-emitting trivalent iridium complex [Ir(MDQ)2(acac)] based on the double-EMLs device.Finally,high performance red EL device with the structure of ITO/MoO3(3 nm)/TAPC(40 nm)/Ir(MDQ)2(acac)(2.0 wt%):TcTa(10 nm)/Ir(MDQ)2(acac)(2.0 wt%):26DCzPPy(10 nm)/TmPyPB(40 nm)/LiF(1 nm)/Al(100 nm)were fabricated.The maximum current efficiency,power efficiency,and external quantum efficiency(EQE)was 44.76 cd/A,40.19 lm/W,15.5%,respectively.Even at the high brightness of 1000 cd/m2(5.2 V),current efficiency as high as 40.59 cd/A(EQE=14.4%)can still be retained by the same device.