Near infrared organic light-emitting diodes based on acceptor-donor-acceptor (ADA) using novel conjugated isatin Schiff bases

Fabrications of a single layer organic light emitting diodes (OLEDs) based on two conjugated acceptor-donor-acceptor (ADA) isatin Schiff bases are described. The electroluminescent spectra of these materials range from 630 to 700 nm and their band gaps were measured between 1.97 and 1.77 eV. The measured maximum external quantum efficiencies (EQE) for fabricated OLEDs are 0.0515% and 0.054% for two acceptor-donor-acceptor chromophores. The Commission International De L’Eclairage (CIE) (1931) coordinates of these two compounds were attained and found to be (0.4077, 0.4128) and (0.4411, 0.4126) for two used acceptor-donor-acceptor chromophores. The measured I-V curves demonstrated the apparent diode behavior of two ADA chromophores. The turn-on voltages in these OLEDs are directly dependent on the thickness. These results have demonstrated that ADA isatin Schiff bases could be considered as promising electroluminescence-emitting materials for fabrication of OLEDs.     

Samarium(III) picrate tetraethylene glycol complex: Photoluminescence study and active material in monolayer electroluminescent

A mononuclear Sm(III) complex involving Pic and EO4 (where Pic=picrate anion and EO4=tetraethylene glycol) has been studied. It shows a bright-orange emission when used as active material in a monolayer electroluminescent device of ITO/EO4-Sm-Pic/Al. The crystal structure of the complex consists of [Sm(Pic)₂(H₂O)(EO4)]⁺ cation and [Pic]⁻ anion. The Sm(III) ion is coordinated with nine oxygen atoms from one EO4 ligand in a pentadentate mode, two Pic anions each in bidentate and monodentate modes, and one water molecule. Both the terminal alcohol groups of the acyclic EO4 ligand were involved in the O-H…O hydrogen bonding by infinite one-dimensional (1D) chain within a symmetry direction [0 1 0]. The photoluminescence (PL) spectrum of the thin film shows the typical spectral features of the Sm(III) ion (⁴G_5/2→⁶H_7/2 transitions). The root-mean-square (rms) of the roughness of thin film is 30.605 nm and indicates that the formation of the monolayer electroluminescent device is not uniform and retains a high crystallinity. Typical semiconductor current-voltage (I-V) property was also observed in this device with threshold and turn voltages of 2.8 and 6.2 V, respectively. The [Sm(Pic)₂(H₂O)(EO4)](Pic)·H₂O complex can be applied as a luminescent center in OLED for bright-orange emission.     

Efficient white organic light-emitting diodes based on an orange iridium phosphorescent complex

Stable and efficient white light emission is obtained by mixing blue fluorescence and orange phosphorescence. The introduction of double exciton blocking layers brings about well confinement of both charge-carriers and excitons in the emission layer. By systematically adjusting blue fluorescent and orange phosphorescent emission layers thickness, carriers in emission zone are balanced, and electrically generated excitons can be efficiently utilized. One white device with power efficiency of 14.4 lm/W at 100 cd/m² has excellently stable spectra. The improvement of performance is attributed to efficient utilization of the excitons and more balance of charge-carriers in emission layer.     

Rubrene薄层的位置对器件发光性能的影响及器件内激子复合区域的分析

通过在主体材料上蒸镀一层荧光染料超薄层的方法,研究了有机小分子5,6,11,12-tetraphenyl-naphthacene(rubrene)薄层在器件中不同位置时,有机电致发光器件(OLED)的电致发光光谱及发光性能.实验发现当rubrene薄层位于NPB/AlQ界面处时,器件的发光几乎都来自rubrene的发光...     

不同主体材料对红色磷光OLED器件性能的影响

制作了结构为ITO/2T-NATA (20 nm)/NPB(60 nm)/Zn(BTZ)₂ : Ir(DBQ)₂(acac) (80 nm)/Alq₃(70 nm)/LiF(1 nm)/Al(200 nm)的红光器件,其中2T-NATA是4,4',4″-tris(N-(2-naphthyl)-N-phenyl-amino)-triphenylamine,NPB是N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine, Zn(BTZ)₂是Bis-(2-(2-hydroxyphenyl) benzothiazole)zinc,Ir(DBQ)₂(acac)是iridium complex,Alq₃ 是tris(8-hydroxyquinolato)aluminum。基于Ir(DBQ)₂(acac) 掺杂的Zn(BTZ)₂体系的器件给出最高电致发光(EL)性能。结果显示:10％Ir(DBQ)₂-(acac) 掺杂Zn(BTZ)₂器件的亮度和效率分别为25 000 cd/m²和12 cd/A,其相应的EL峰位于620 nm,色坐标(x=0.63,y=0.37)。由于未使用激子阻挡层,所以,比通常磷光器件的制作工艺简单并且操作过程容易控制。     

微腔有机电致发光器件的角度依赖性

设计并制作了两个器件,一个是微腔有机电致发光器件(MOLED):G/DBR/ITO/NPB(46 nm)/DPVBi(20 nm)/Alq₃(56 nm)/LiF(1 nm)/Al(150 nm);一个是无腔器件(OLED):G/ITO/NPB(46 nm)/DPVBi(20 nm)/Alq₃(56 nm)/LiF(1 nm)/Al(150 nm)。测试并分析了器件性能。OLED在电流密度30 mA/cm²时的电致发光(EL)光谱随观测角度由0°~70°都是一宽谱带,是发光层DPVBi的特征发光谱,峰值都在452 nm处,半峰全宽均为70 nm,色坐标均为(x=0.18,y=0.19),无腔器件没有角度依赖性。相同电流密度下,微腔器件的EL谱随观测角度由0°~70°,发光峰值蓝移,由472 nm逐渐移至428 nm;峰值相对强度渐弱,由0.32变至0.02;半峰全宽由14 nm增加至120 nm;色坐标由(x=0.14,y=0.10)变至(x=0.19,y=0.25),颜色由紫蓝变成蓝白到接近白色。微腔器件具有明显的角度依赖性。     

Some spirobiindane based 1H-pyrazolo [3,4-b] quinoline chromophore as novel chromophore for light-emitting diodes

An influence of phenoxy groups for the luminescent and electroluminescent properties of spiro-compounds with pyrazolo [3,4-b] quinoline structure (fluorophore) chromophore has been studied. All the compounds exhibit strong fluorescence in solution and in solid state as well. The prepared compounds were used as dopant chromophore in PVK polymer matrices for electroluminescent (EL) and light-emitting diode (LED) devices with configuration ITO/PEDOT-PSS/PVK/PQ/Ca/Al. Role of the bathochromic shifts and solvent polarity in absorption and photoluminescent maxima is considered. Relation between the number of pyrazoloquinoline chromophore and presence of phenyl group on the fluorescence spectra is explored. Polarizability of the particular pyrazoloquinoline compounds on the solvatochromic effects is investigated. Possible ways of enhancement of the brightness in the light-emitting properties of the mentioned chromophore are discussed.     

MoO_3作空穴注入层的有机电致发光器件(英文)

研究了三氧化钼(MoO3)薄层作为有机电致发光器件空穴注入层的器件性能和注入机制。发现1nm厚度下发光器件性能最佳,器件的最大电流效率比对比发光器件的最大电流效率提高1.6倍。器件的电容曲线表明MoO3薄层能有效提高空穴载流子的注入,多数载流子开始注入的拐点大约降低了9V。单空穴载流子电流曲线说明MoO3器件的电流注入是空间电荷受限电流注入机制,MoO3使阳极界面处形成欧姆接触,而对比器件的电流注入是陷阱电荷受限电流注入机制。器件的光伏曲线进一步说明器件性能的提高是由于MoO3层能使阳极界面能级分布发生改变,1nmMoO3厚度下器件的内建电势从对比器件的0.25V提高到了0.8V,有效降低了空穴注入势垒,提高了器件性能,但过厚的MoO3层由于增加了器件的串联内阻,会导致器件性能降低。     

中间层对白色全磷光有机电致发光器件性能的影响

制备了基于蓝色磷光材料bis[3,5-difluoro-2-（2-pridyl）phenyl-（2-earboxypyribyl）iridumⅢ]（FIrpic）、红色磷光材料bis（2-methyldibenzo [f,h]quinoxaline）（acetylacetonate）iridium（Ⅲ）（Ir（MDQ）₂acac）的双波段白光有机电致发光器件。蓝色磷光材料FIrpic被掺杂在一种宽带隙的主体材料1,3-bis（triphenylsilyl）benzene（UGH3）之中,红色磷光材料Ir（MDQ）₂acac被掺杂在主体材料4,4',4"-tris（carbazol-9-yl）triphenylamine（TCTA）之中,并在两发光层之间加入一种宽带隙的空穴传输材料1,3-bis（carbazol-9-yl）benzene（mCP）作为中间层。制备的器件结构为ITO/NPB（40 nm）/TCTA：Ir（MDQ）₂acac 7%（10 nm）/mCP（x nm）/UGH3：Firpic 8%（30 nm）/BPhen（30 nm）/LIF（0.8 nm）/AL（200 nm）。实验结果表明,中间层的加入促进了发光层中电子和空穴的平衡并抑制了发光层之间的能量转移。加入适当厚度的中间层之后,器件的性能得到了明显的提升,相比于无中间层器件,最高电流效率由3.4 cd/A提高到13.2 cd/A。     

微腔有机电致发光器件角度依赖性的模拟与实验验证

为了分析微腔有机电致发光器件(MOLED)发光的角度依赖性,根据微腔计算公式,采用传输矩阵法进行了模拟计算,并进行了实验验证。所设计器件的结构为Glass/DBR/ITO(58 nm)/NPB(46 nm)/DPVBi(20 nm)/Alq₃(56 nm)/LiF(1 nm )/Al(150 nm)。由实验得到的电致发光(EL)谱可以观察到:随着探测角度的加大,发光峰蓝移、强度减小。与模拟得出的不同观测角度下的反射谱进行比较,发现透射峰值与EL峰值相对应。模拟分析发现,这是由于观测角不同,微腔两个反射镜的S和P偏振的反射率及反射相移不同,同时腔内光学厚度发生变化,即微腔长度变化共同作用所导致。