| White organic light-emitting devices (WOLEDs) are considered as one of the mostpromising high-tech in the 21st century due to their versatile applications in full-colordisplays, liquid crystal display (LCD) backlights, solid state lighting and so on. The mostimportant advantage for OLEDs should be flexible characteristics comparing with otherdisplay panels. Therefore, developing flexible WOLEDs is significant. The main work of thispaper is utilizing the color conversion method to achieve pure white FOLEDs. However, thekey role for the white light devices is to achieve the higher brightness and efficiency of blueFOLEDs as an exciting light source, which is related to the primary research our works focuson. The main results of the article include three aspects as below:1. The ability of holes injection and transport could be improved by introducing thenovel multiple quantum well (MQW) structures of F4-TCNQ/m-MTDATA in the FOLEDs,and the electroluminescent (EL) performances of FOLEDs have been improved by thisapproach. We compared and analyzed the EL performances of FOLEDs with differentquantum well (QW) numbers, then the optimum devices could be achieved (n=2). Theoptimum double quantum well (DQW) device exhibits aseries of maximum values: abrightness of 23, 500 cd/ m2at 14 V, a current efficiency of 7.0 cd/A at 300.3 mA/cm2, and apower efficiency of 4.46 lm/W at 0.24 mA/cm2, respectively, which are greatly improved by114% and 56% compared with the maximum brightness and the maximum current efficiencyfor the conventional device without MQW structures. Moreover, relevant theory explanationfor this improvement has also been put forward based on the effect of interfacial dipole andinterfacial doping between F4-TCNQ and m-MTDATA.2. The new blue fluorescent material NCA is used to fabricate highly efficient blueFOLEDs based on the novel MQW structures, with which the red color conversion material4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)is combined to actualize white FOLEDs. We compared and investigated theelectroluminescent (EL) characteristics of the blue FOLEDs with different QW numbers, andthe devices with the optimal number of quantum wells (n=2) exhibit optimum ELperformances. The maximum brightness and current efficiency are 9, 450 cd/m2at 14 V and5.0 cd/A at 1.96 mA/cm2, respectively. Then, a high color stability of white light emissioncould be achieved based on the blue FOLEDs combining with the different thickness ofDCJTB. The experimental results demonstrated that the CIE coordinates of (0.33, 0.27) wasobtained at the driving voltage of 7 V with the thickness of DCJTB of 120 nm, which wasvery close to the white equal-energy area. Moreover, the CIE coordinates migration of theflexible WOLED was less than (±0.02,±0.02) at a wide range of driving voltages (from 6 Vto 11 V) for the devices, which indicates that the flexible WOLEDs present excellent color stability.3. The higher brightness and efficiency of blue FOLEDs could be achieved by employingthe doping method consisting of the ADN host doped with NCA dopant. In this work, wecompared and investigated the EL performances of the four types of FOLEDs with differentdoping concentration. The experimental results demonstrated that these devices with the theoptimum doping concentration of 5% show better characteristics. The maximum brightnessand current efficiency of the blue FOLEDs are 14, 720 cd/m2at 12 V and 10.6 cd/A at 0.12mA/cm2, respectively. Furthermore, the optimum blue devices are combined with the differentthickness of DCJTB to achieve the pure white light emission with better color stability. |
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