WOLED Based On Quantum Well Structure And Thermally Activated Delayed Fluorescence

OLED have achieved the production of industrial application in the fields of display and lighting, but there are still some problems with OLED. Especially WOLED, the problems of luminous efficiency, roll-off and spectral stability need to be solved urgently. Based on the problems mentioned above, in order to improve the efficiency and roll-off and achieve stable white spectra, the paper focused on the WOLED and carried out the research from two aspects of new device structure design(quantum well structure) and new application of luminous mechanism(thermally activated delayed fluorescence, TADF). Therefore, I carried out three sections research as follows:The first section: In order to study the influence of quantum well structure on device performance, I begin designed the red phosphorescent OLED with quantum well structure. Compared to the traditional structure, the efficiency improved 21%. I found that the quantum well structure could confine carriers and excitons. Further, I designed firstly fluorescent/phosphorescent hybrid three colors emission WOLED with Ι-type and Π-type quantum well structure in order to study the influence of different types quantum well structure on device performance. I found the Ι-type quantum well structure could confine electrons and holes in emission potential well layer better than Π-type, which improved the recombination efficiency of carriers. But the spectral stability was poor with three colors emission, the intensity of emission peak would change with increased voltage. Finally, color stable two colors emission WOLED with Ι-type quantum well structure was achieved by further design. From 8 V to 14 V, the change of CIE coordinates were(0.397±0.002, 0.414±0.008). I found quantum well structure balanced the transport of carriers in emitting layer. Meanwhile, the WOLED improved the efficiency roll-off at high current density. The efficiency roll-off improved ~15% and I found the quantum well structure could confine carriers and excitons in each emitting layer and excitons concentration in all emitting layers was diluted, which decreased the TTA.The second section: Begin earning the blue and orange exciplexes with TADF emission through time resolved PL spectra and transient PL decay measurements. Further, achieving tandem orange OLED with exciplex TADF emission by efficient design of charge generation layer. Based on the tandem orange OLED, I designed the full exciplex TADF emission tandem WOLED and the device achieved the maximum EQE of 9.17%, which was much higher than the WOLED based on exciplex emitter reported up to now. The achievement of high efficiency was attributed to the TADF contribution of blue and orange exciplexes. Meanwhile, the WOLED exhibited warm white emission with high spectral stability. From 6 V to 14 V, the change of CIE coordinates were only(0.41±0.003, 0.44±0.002). I found this was because of the balanced transport and recombination of carriers in emitting layer. Next, I designed single fluorescent WOLED with intramolecular TADF material as the blue host and traditional fluorescent material as the orange dopant. The device achieved the incomplete energy transfer from host to dopant by the control of concentration. The emission hybrid of host blue and dopant orange got the white. The WOLED achieved the maximum EQE of 7.48%, which broke the traditional fluorescent EQE limit(5%). I found the achievement of high efficiency was attributed to triplet excitons up-conversion of TADF host by the measurement of transient PL decay. Meanwhile, a stable white spectra also earned. The CIE coordinates changed from(0.359, 0.439) to(0.358, 0.430) when voltage increased from 5 V to 8 V. I found the design of donor-acceptor units in TADF host balanced the transport and recombination of carriers in emitting layer.The third section: I designed ultra high-efficiency red emission fluorescent OLED with TADF exciplex TCTA: 3P-T2 T as the host and traditional fluorescent material DCJTB as the dopant. The maximum luminance, current efficiency, power efficiency and EQE were 22767 cd/m2, 22.7 cd/A, 21.5 lm/W and 10.15%, respectively. The EQE of 10.15% was much higher than the fluorescent OLED reported up to now using DCJTB as an emitter. The transient PL decay analysis revealed the achievement of such high efficiency were due to the triplet excitons up-conversion of TADF exciplex host and the efficient F?rster energy transfer from host to dopant. Next, I plan to achieve highly efficient and high color stable WOLED by utilizing the ultra high-efficiency DCJTB emission.