【作者】 张宏梅；

【导师】 石家纬；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2006， 博士

【摘要】 本论文分别在理论和实验上设计了DBR结构,用DBR与金属镜构成微腔,研究了微腔结构对有机电致发光器件的光电特性的影响。理论和实验研究表明,介质镜的反射率和截止带宽及其阻带中心波长的位置对有机电致发光器件的发光颜色、亮度和效率都有很大的影响。根据理论分析和实验验证,设计了具有阻带带宽200nm,中心波长在540nm处,反射率80%的DBR,用其与金属AL构成微腔,用8-羟基喹啉铝(Alq3)做电子传输/发光层,NPB做空穴传输层只简单地改变有源层及金属层的厚度,就可以容易地实现红、橙、黄、绿、蓝不同发光颜色的有机发光二极管,同相同结构的非微腔器件相比,微腔器件的性能得到了改善,红、橙、黄、绿光微腔器件的亮度和效率分别提高了1.5倍左右是目前文献报道的用DBR与AL形成有机微腔发光二极管获得的最好结果。设计了窄阻带同时具有两个次阻带的特殊传输特性的DBR,为获得性能较好的微腔发光二极管提供了新的途径;另外,用具有双阻带的DBR构成多模谐振微腔,首次实现了包含分立的红、绿、蓝3个窄发射峰的高效率的微腔白光有机发光器件。更多还原

【Abstract】 Recently, organic light-emitting diodes (OLEDs) based on organic materialsare one of the most promise technology for flat-panel displays because of thecharacteristics of high efficiency, low voltage operation, wide-viewing angle,simple fabrication process, surface emitting-light, easily realizing of large-area,full-colour and flexibility displays. However, the broad emission spectra due bothto vibronic sidebands and strong heterogeneous broadening of the transitions insuch organic systems result in difficulties in developing full color displays.Researchers explore many approaches to realize monochrome light emission,including the use of color filter and microcavity structures, and consider that themicrocavity structure is a main method with most potential and extensive.Incorporation of the microcavity structure into OLEDs is demonstrated not onlyto narrow emission, which enhances the color purity, but also to enhance deviceefficiency due to the intensity enhancement of the spontaneous emission over alarge range of angles by the microcavity effect. It can be noticed that microcavitystructures have greatly influence on the performance of OLEDs.In this thesis, we simply analyzed the transmission theory of optical thinfilm, and simulated the transmission characteristics of distributed Bragg reflectors(DBR) based on the transmission matrix model using Matlab software. Therelation between reflectivity, reflective bandwidth and refraction index difference,layer number and sequence of high-low medium of DBR were studied. Theobtaining simulated result provided theoretical advices for actual design of themicrocavity formed by dielectric mirror (DBR) in OLEDs. Basis on this, wetheoretically studied luminescence characteristics of the microcavity OLEDs. Theemission spectrum and angle relationship characteristics and the effects of thecavity –length and the reflectivity of DBR on spectral characteristics, and theselecting mode characteristics of the microcavity were simulated. It was foundtheoretically that the introduction of the microcavity into OLEDs narrowsemission spectrum, at the same time, also significantly enhances the emissiveintensity, and the emissive intensity is reduced when emission spectrum moves toshort wavelength with increasing view-angle. It was also found that changingcavity-length may realize not only single mode emission, but also multimodeemission. The modification of spontaneous emission by microcavity and theselection effect of microcavity are observed well.DBR mirrors with different reflection central wavelengths, differentreflectivity and different reflective bandwidth were designed, and microcavityOLEDs based on tris(8-hydroxyquinoline) aluminum (Alq3) as the emitter andN,N’-di(naphthalene-1-yl)-N,N’-diphenyl-benzidine (NPB) as thehole-transporting layer were fabricated by using the Fabry-Perot microcavityformed metal electrode aluminum (Al) and DBR mirrors. Some effects ofreflection central wavelengths, reflectivity and reflective band width of DBR, andthickness of metal mirror on the electroluminescent (EL) spectrum andperformance, and the angular dependence of the EL spectra were investigated. Itwas found experimentally that the emissive color depends strongly on theproperties of the dielectric mirror and the thickness of the metal mirror.Obviously, the central wavelength of the dielectric mirror plays a great role onemissive color of microcavity-based OLEDs. Thus the realization of differentcolor light emission becomes possible by carefully designing stop-band centralwavelength of DBR and OLED structure, which is very useful in practicalapplication. It was found in the studies of the effects of DBR reflectivity onperformance of OLEDs that the DBR with low reflectivity not only emits singlemode spectrum, but also improves significantly the EL efficiency. Afteroptimizing the thicknesses of organic layer and metal cathode, the EL efficiencyreached 8.3 cd/A, which is enhanced by 6.4 times compared with devices withhigh reflectivity DBR. Based on the above analysis , we designed special DBRhaving a narrow central stop-band at 538 nm with a stop-bandwidth of 80 nm anda reflectivity of 80%, and two stop-bands, respectively, at 457 nm and 652 nm,the use of the DBR not only narrows emission spectrum, FWHM is only 7nm, butalso enhances efficiency of device, and the strong angular dependence ofemissive wavelength is greatly reduced. It was found that the EL emissive colordid not strongly depend on the thickness of the organic layer and metal layer,which is useful for optimizing configuration of device. It was also found thatproperly increasing the thickness of metal mirror in microcavity can furthernarrow emission spectrum, and the angular dependence of the emissivewavelength was also reduced at a certain extent.Furthermore, effective red, orange yellow, yellow green and white emissionOLEDs were realized by careful selection of the DBR configuration. Comparedwith noncavity devices, the EL performance of microcavity devices is greatlyimproved. Basis on the DBR with bandwidth 200nm and reflectivity 80%, andthe structure of NPB/Alq3 bilayer, red, orange yellow, yellow green microcavityOLEDs were realized by simply changing the thickness of the active layer andmetal layer. The fabricated microcavity OLEDs, respectively, emit at peakwavelengths of 610 nm 592 nm 577nm 540nm and 466nm with 27 nm 21nm21.5nm 20 nm and 20nm full width at half maximum (FWHM). The CIEcoordinates from vertical cavity axial surface, respectively, are(0.54,0.42)(0.58,0.367()0.35,0.54)(0.21,0.60) and (0.15,0.16).The maximum brightnessand the maximum current efficiency, respectively, are 7000 cd/m2 3.7 cd/A,7800.0 cd/m24.5cd/A, 18100 cd/m28.6 cd/A,30000 cd/m27.8 cd/A, 7000.0 cd/m22cd/A, which respectively are over 1.5 times1.58 times and 1.47 times higherthan those of the same structure noncavity OLEDs. At current density 100.0mA/cm2, brightness and current efficiency for orange, yellow and greenmicrocavity devices are also over 1.5 times higher than those of the samestructure noncavity OLEDs.In order to realize the more high red OLEDs, doping method was used tofabricate microcavity OLEDs. A single-mode red light emission at peakwavelength of 610 with about 25 nm of full width at half maximum (FWHM)were realized very well in the forward direction, and a weak angular dependencewas observed. The Commission Internationale De L’Eclairage (CIE) chromaticitycoordinates do not show obvious variation, at least it is not detectable to eye. TheCIE coordinates are (0.60,0.34) for 00, (0.60,0.35) for 100, (0.59,0.36) for 200,(0.55,0.38) for 300, (0.54,0.40) for 400. The emission at all the viewing anglesshows the approximately same red color light. The maximum brightness and ELefficiency reached 37000 cd/m2 and 13.7 cd/A (13.3 lm/W), respectively, whichare higher than the brightness of 29700 cd/m2, the current efficiency of 9.0 cd/Aand the power efficiency of 9.4 lm/W for the noncavity devices. At 100 mA/cm2current density, the microcavity devices emitted the brightness of 9000 cd/m2 andcurrent efficiency of 8 cd/A, which are enhanced by 1.3 times with respect to thebrightness of 6900 cd/m2 and current efficiency of 6 cd/A for noncavity devices.In addition, multi-mode resonance cavity was fabricated by using metalmirror and DBR with double stop band. Efficient white microcavity OLEDscomprising of individual red green and blue three narrowed emission peak wererealized The maximum brightness arrived at 1940 cd/m2 at a current density of200.0 mA/cm2, and the maximum current efficiency reached 1.6 cd/A at a currentdensity of 12 mA/cm2, which are over 1.6 times higher than those of the samestructure noncavity.In conclusion, the reasonable design of microcavity in OLEDs not onlynarrows the emissive spectrum, but also improves the EL performance. It is surethat the studies of microcavity OLEDs will become an important director inOLED displays, and are significant by theoretically and experimentallyoptimizing the performance of OLEDs.更多还原