The Study Of Solution Processed High Performance Electrofluorescent White Organic Light Emitting Device And Its Application

Due to the potential applications in the field of display and solid-state-lighting, as well assimple preparation technology, and a wealth of material system, white organic light-emittingdiodes (WOLED) has attracted extensive attention not only in the scientific community butalso industry. However, at present, all commercialized OLED products are based on smallmolecular material by vacuum vapor deposition process. The disadvantage of this kind oftechnology is the huge capital for equipment investment, serious waste of materials, very lowyield, and difficult to achieve large area. While solution processing (e.g.,inkjet printing, spincoating, and dip coating, etc.) could just compensate for the lacks of vacuum depositionprocess. In most cases, however, the solution process technology is focused on organicfunction layers. If we want to get rid of the shackles of vacuum deposition equipmet, thetechnology of solution process metal cathode has to be considered. In addition, although theinternal quantum efficiency of phosphorescent material can reach100%, the stability is still astumbling block to their development. Therefore, in order to obtain stable and efficientdevices, many scientists still focus on developing of fluorescent material system. For thisreason, the main text of this paper is based on the solution process fluorescent materials,through optimizing the device structure, the highest efficient WOLED device was produced;fully soltion processing PLED including metal cathode was studied, and patterning anode forflexible OLED, at last, we researched their application form designing and preparing largewhite back light panel.Firstly, we studied the highly efficient, solution-processed WOLEDs based onfluorescent small molecules. The light-emission layer is realized by doping a fluorescentπ-conjugated blue dendrimer host (the zeroth generation dendrimer, G0) with ayellow-emitting fluorescent dopant oligo(paraphenylene vinylene) derivative CN-DPASDBwith a doping ratio of100:0.15(G0:CN-DPASDB) by weight. Our early study shows that G0device is hole dominated. Therefore, it‘s critical to suppress the holes while increase theelectrons to improve the device performance. To suppress excessive holes, thehigh-conductivity hole injection layer (PEDOT:PSS AI4083) is replaced by thelow-conductivity PEDOT:PSS CH8000. To facilitate the electron injection, a hybrid electroninjection layer is introduced by doping solution-processed cesium fluoride (CsF) into amethanol/water soluble conjugated polymerpoly[(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFNR2). The device achieves a maximum luminous efficiency of17.0cd A-1and a peak power efficiency of15.6lm W-1at (0.32,0.37) with a color rendering index of64. The deviceefficiency is highest ever reported for WOLEDs based on solution-processed fluorescentsmall molecules, which is also on par with the efficiency achieved by the thermallyevaporated fluorescent small-molecules.In order to get rid of the shackle of vacuum deposition equipmet, we introducedall-solution processed polymer light-emitting diode by solution-depositing the cathode andutilizing a multifunctional buffer layer between the cathode and the solution processedorganic layers. The buffer layer, which offers the functions of solvent-proof electron injectionand proper affinity, is fabricated by mixing the water/alcohol-soluble polymer PFNR2and acurable epoxy adhesive. The all-solution process eliminates the need for high vacuum forthermal evaporation of the cathode, which greatly reduced the production cost of organiclight-emitting diodes (OLEDs).To achieve roll-to-roll manufacturing, flexible substrates are needed. The application ofsolution process technology in flexilbe OLED making it possible to achieve wearable fantasydisplay in the future. There is a lot of problems in studying FOLED, the first problem ispatterning ITO anode. In the etching processing, the ITO film teared easily for the fragileproperty of ITO material. At last, bringing large leakage to the OELD devices. Especially,traditional etching processing, which possesses many steps and needs high temperatureannealing, make the ITO film crack much easier. To solve this problem, we invent a newetching method. Compared to traditional method, the new method which has fewer steps andlower temperature annealing is suitable for flexible OLED. In fivth section, we comparedflexible OLED devices‘J-V-L and LE-J characteristics curve between traditional and newetching method. Owing to the simple operation upon new etching mehod, the ITO film wassmooth and without burr and pinhole, the performance of flexible OLED devices are close tothe glass substrate devices. Based on the successful on subsize device, we designed and madeone inch red, green and white flexible OLED based on solution process.Moreover, for the application of WOLED, based on the Dr Junhong Zhou‘s work[1], wefurther improved the performance of lager area white back panel through adjusting thearrangement of metal grid in lighting area and treating organic layer with methnol or ethnolbefore evaporating metal cathode. We successfully prepared better performance four inchlager area white back panel.