| With the rapid development of science and technology,organic light-emitting device(OLED)will bring flat-panel displays and solid-state lighting industry into an era of high quality.In order to enhance its competitiveness,the research and development of blue OLED devices with excellent performance,simple fabrication process and longer lifetime are particularly important.Therefore,this paper is to employ a simple and effective method to improve luminance and efficiency of blue OLED(we reduced the turn-on voltage and improved luminance in the first part,and improved brightness and efficiency in the second and third parts)as the goal to carry out the following research work.1.By annealing the pentacene film as the hole injection layer at 120?,the EL performances of the blue fluorescent organic light-emitting device are improved.The optimal device with the pentacene film annealed at 120? and n-doped electron transporting layer(ETL)structure exhibits a low turn-on voltage of 2.6 V and a driving voltage of 5.1 V at 1000 cd/m~2,which are reduced 0.9 V and 1.4 V compared with that of the control device(without thermal annealing).It presents a high luminance of 134800 cd/m~2 at 12 V which is 1.5 times higher than that of the control device at 12 V.The driving voltages of these devices can be reduced markedly,which is mainly attributed to the effect of thermal annealing on pentacene film.The thermal annealing could induce pentacene to develop into high crystallinity films,and pentacene molecules can form a highly-ordered,large-sized and smooth lamellar shape grown on the ITO substrate.Meanwhile,an n-doped ETL enhances the electron transporting ability of the devices,which improves the injection and their balance of the two types of carriers(holes and electrons)for realizing a high luminance of the devices.2.A novel exciton feedback effect has been observed by introducing the bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(BAlq)inserted between the emitting layer(EML)and ETL in blue OLEDs.As an exciton feedback layer(EFL),BAlq does not act as a traditional hole blocking layer.The design of this kind of device's structure can greatly reduce exciton's quenching due to accumulated space charge at the exciton formation interface.Meanwhile,the non-radiative energy transfer from EFL to the EML can also be utilized to enhance the exciton's utilization,which is confirmed by the test of photolumimescent(PL)transient lifetime decay for these devices.Accordingly,the optimal device presents the improved performances with the maximal current efficiency of 4.2 cd/A and the maximal luminance of 24,600 cd/m~2,which are about 1.45 times and 1.75 times higher than those of the control device without the EFL,respectively.Simultaneously,the device shows an excellent color stability with a tiny offset of the CIE coordinates((35)x=±0.003,(35)y=±0.004)and a relatively lower efficiency roll-off of 26.2% under the driving voltage varying from 3 V to 10 V.3.We insert different charge control layers in various positions of the emitting layer.The optimal device has two layers of BAlq as charge control layers with different synergistic functions.The emitting region can be divided into two parts by inserting the first charge control layer,and the exciton recombination zone could be expanded accordingly.Furthermore,this charge control layer can prevent the transport of holes to ameliorate the balance of the carrier distribution.Holes could be availably confined in the emitting layer by inserting the second charge control layer between the emitting layer and the electron transport layer,which improves the utilization rate of the exciton.The two charge control layers can block holes meanwhile expand exciton recombination zone.Eventually we fabricated the blue OLED device with high efficiency and high luminance.The maximum brightness and current efficiency of the optimal device were 48220 cd/m~2 and 6.72 cd/A,which were increased by 99.3% and 89.3% compared to those of the control device. |
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