以萘为π-中心的双芪类衍生物的电致发光特性研究

以自制的"D-π-D"对称型有机绿色发光分子1,4-双(4'-N,N-二甲基氨基苯乙烯基)萘(简称 BMABN)为发光层,在结构为ITO/NPB/BMABN/BCP/Mg∶Ag的器件中,研究了空穴阻挡层厚度对器件发光性能的影响.结果表明,空穴阻挡层的增厚使得器件的起亮电压有所增加,但器件的亮度、电流效率和稳定性显著增加.该器件在5V开启,18V电压下亮度和效率分别为2000cd/m2和0.4lm/W.     

高效单发光层绿色有机发光二极管的制备与性能研究

为了提升绿色有机发光二极管的效率,设计了阶梯能级结构的器件,使得载流子在器件中更有效传输,进而有效减缓了器件效率的衰减。选择热致延迟荧光材料(4s,6s)-2,4,5,6-四(9-氢咔唑-9-基)间苯二腈(4CzIPN)作为发光材料,并将其掺杂到能级匹配的主体材料1,3-二(咔唑-9-基)苯(mCP)中构成发光层,制备了一系列单发光层的绿色有机发光二极管。在发光材料的掺杂浓度为2%(wt,质量分数),发光层的厚度为20nm条件下,制得的器件性能最佳,其启亮电压为3.4V,其最大亮度、电流效率、功率效率和外量子效率分别为20706cd/m~2、50.49cd/A、41.96lm/W和16.7%。在亮度为1000cd/m~2条件下,其电流效率和外量子效率仍然高达34.06cd/A和11.6%。器件显示主峰位于504nm的4CzIPN特征发射,随着掺杂浓度的提升,越来越多的电子和空穴被4CzIPN分子所俘获,导致主体材料mCP的特征发射峰逐渐减弱。     

红荧烯衍生物的红光电致发光器件及其在照明中的应用

合成了一种红荧烯的衍生物,2-甲酰基红荧烯作为一种红光掺杂剂,掺杂在N,N-diphenyl-N,N-bis 1-naphthyl–1,1-biphenyl-4,4-diamine(NPB)中制备的电致发光器件,发射峰位于598nm,电流效率为2.1cd/A。用这个红光掺杂系统制备了一个白光电致发光器件,在白光器件中,2-甲酰基红荧烯,八-羟基喹啉铝(Alq3),以及NPB分别组成了白光中的红、绿以及蓝的发光成分,获得了一个白光器件,该器件显色指数高达89.8,在11V时,色坐标达(0.33,0.33),最大亮度为5000cd/m2以及最大发光效率为4.7cd/A。这些性能参数表明这个白光器件具有潜在的照明应用。另外,还讨论了器件的结构设计以及电致发光过程及机理。     

新型钙镁铝合金阴极对红光OLED性能的影响研究

采用不同比例的Ca/Mg/Al合金和纯Ca/Al合金阴极分别制备结构为ITO/Mo O_3(30nm)/NPB(40nm)/TCTA(10nm)/CBP:R-4B(30nm)/TPBI(10nm)/Alq3(30nm)/Ca:Mg(X%):Al(100nm)和ITO/Mo O3(30nm)/NPB(40nm)/TCTA(10nm)/CBP:R-4B(30nm)/TPBI(10nm)/Alq3(30nm)/Ca:Al(100nm)的红光有机电致发光二极管(OLED)器件及其对应的电子型器件,研究了阴极材料对器件的影响。结果发现,Ca/Mg/Al合金阴极可以提高阴极发射电子能力。当Mg掺杂质量比为20%时,器件具有最优性能,在电压为13 V时,发光亮度为10250 cd/m2,电流密度为57.099 m A/cm2,最大电流效率为18.8426 cd/A,效率较高且滚降比较平缓。原因为载流子注入比较平衡,形成了较多的激子。     

空穴注入层MoO_3厚度对蓝绿色磷光OLED发光特性的影响

以mCP为磷光主体材料,BGIr1为蓝绿色磷光掺杂材料,MoO3为空穴注入材料,制备5种不同厚度的MoO3蓝绿色磷光有机电致发光器件(OLED),并研究不同厚度MoO3空穴注入层对蓝绿色磷光OLED发光特性的影响。所制器件结构为ITO/MoO3(x nm)/NPB(40nm)/mCP∶BGIr1(30nm,18%)/BCP(10nm)/Alq3(20nm)/LiF(1nm)/Al(100nm),其中18%为发光层中BGIr1的掺杂量(质量分数),x为空穴注入层MoO3的厚度。研究结果表明,本实验制备器件空穴注入层MoO3的最佳厚度为20nm。当电压为13V时,MoO3厚度为20nm器件获得最大亮度为8 617cd/cm2,当电流密度为20mA/cm2时,器件获得最大发光效率为5.7cd/A。器件在488和512nm处获得两个主发射峰,发光颜色稳定,CIE坐标为(0.19,0.21)。     

咔唑和二氰基蒽掺杂纳米粒子的制备及光学性质

以蓝光染料咔唑为电子给体,黄光染料9,10-二氰基蒽为电子受体,采用再沉淀法制备了咔唑和二氰基蒽等摩尔掺杂的纳米粒子。掺杂纳米粒子与纯咔唑聚集体或二氰基蒽聚集体的形貌和发射光颜色明显不同,说明咔唑和二氰基蒽很好的掺杂到一起。吸收光谱表明咔唑和二氰基蒽在掺杂纳米粒子中没有形成电荷转移复合物,荧光发射光谱和荧光寿命表明咔唑和二氰基蒽在掺杂纳米粒子中形成激基复合物,激基复合物的出现使得掺杂纳米粒子的发射光颜色为橙色。     

一种基于照明目的的有机白光发光二极管

研制了一种以照明为目标的有机白光发光二极管(WOLED),该二极管在8V时的色度坐标为(x=0．319,y=0．337),对应的显色指数(Ra)为85．4,色温(Tc)为6151K。该二极管是含NPB和CBP两个基质的多层掺杂型结构器件;此外,NPB{4,4‘-bis[N-(1-naphthyl)-N-phenylamino]bipheonyl}除了用作绿光和黄光基质外,还用作空穴传榆材料,CBP{4,4‘-N,N‘-dicarbazole-biplaenyl)用作红光磷光配合物的基质材料。3个掺杂层分别提供白光发射的红、黄和绿光成分,而蓝光成分则来自于空穴传榆层NPB本身的发射。该器件在直流电流密度为0．1mA／cm^2时最大白光发光效率可达5．6cd／A(3．9lm／W),在15V时达到的最大亮度为5100ccl／m^2。其性能参数达到了白光照明光源的要求。     

具有双掺杂发射层白光OLED器件结构的研究

白光有机电致发光器件是获得全色器件的基础。制备了一种具有双掺杂发射层的白光OLED器件，其结构为ITO／CuPc／NPB／ADN：TBP以ALQ：DCJTB／ALQ，Mg：Ag，将2，5，8，11-tetra-tertbutylperylen-e（TBPe）掺杂到蓝光主体材料ADN中作为蓝色发光层，4-（dicyanome-thylene）-2-t-butyl-6-（1，1,7，7tetramethyljul-olidyl-9-enyl）-4H-pyran（DCJTB）掺杂到AIQ中作为红色发光层，通过实验结果对比，研究了TBPe以及DCJTB的掺杂浓度对器件性能的影响，确定了当TBPe浓度为3％（质量分数），DCJTB浓度为1．8％（质量分数），时，获得的白光器件性能最优。     

一种新型宽发射材料的合成及其光电性能研究

以2-噻吩甲醛、苯胺及方酸为原料合成了一种新型含噻吩基方酸菁衍生物的宽发射有机电致发光材料——1,3-二(苯基噻吩氨基)方酸(SQ),通过核磁共振、红外光谱和元素分析确定其分子结构。并研究了其光物理性能。研究发现,SQ薄膜的发射光谱位于517nm,半峰宽105nm。将其作为发射材料首次制备了结构为ITO/MoO3(3nm)/NPB(20nm)/SQ(15nm)/TPBi(27nm)/LiF(1nm)/Al(100nm)的发光器件,得到了峰位在520nm,半峰宽为132nm的宽发射光谱。利用其宽发射特性,进一步设计白光器件,其结构为ITO/MoO3(3nm)/CBP(23nm)/TPBi∶SQ(5%,15nm)/TPBi(27nm)/LiF(1nm)/Al(100nm),此器件启亮电压为5V,最大亮度为124cd/m~2(at 13V),最大电流效率为0.12cd/A,CIE为(0.30,0.33)。结果表明,通过在TPBi主体材料中掺杂SQ,利用主客体材料之间发生能量不完全传递,可实现色饱和度好的白光发射。     

高效稳定性有机黄光电致发光器件

主要通过红绿磷光材料R-4B和GIr1掺杂的方法,制备了黄光OLED器件,器件结构为ITO/MoO3(X)/NPB(40nm)/TCTA(10nm)/CBP:GIr1 14%:R-4B2%(30nm)/BCP(10nm)/Alq3(40nm)/LiF(1nm)/Al(100nm),TCTA和BCP分别为电子和空穴阻挡材料,同时结合TCTA和BCP对载流子的高效阻挡作用,研究了MoO3对器件效率和稳定性的影响。发现当增加MoO3的厚度为90nm时,在较大的电压范围内,器件都具有较高的效率和色坐标稳定性。在电流密度为7.13mA/cm2时,器件达到最高电流效率29.2cd/A,亮度为2081cd/m2;电流密度为151.7mA/cm2时,获得最高亮度为24430cd/m2,电流效率为16.0cd/A;器件色坐标稳定性较好,当电压为5、10、15V时,色坐标分别为(0.5020,0.4812)、(0.4862,0.4962)、(0.4786,0.5027)。器件性能的改善主要归因于载流子注入与传输的平衡以及阻挡层对发光区域的有效限定。     

White organic light-emitting diodes utilized by near UV-deep blue emitter and exciplex emission

Numerous investigations have been made into the development of wide color gamut displays for deep-blue OLEDs, including the RGB sub pixels, and white OLEDs (WOLEDs). One of the well known deep-blue emissive dopants, tris(phenyl-methyl-benzimidazolyl)iridium(III) [Ir(pmb)3], successfully introduced its fascinating color coordinate of Commission Internationale de l'Eclairage (CIE) 1931 (0.17, 0.06), however there have been no reports utilizing its accomplishments as WOLEDs. In this report, using only one phosphorescent dopant, the near UV-deep blue emissive Ir(pmb)3, the WOLEDs having the CIE 1931 coordinate of (0.33, 0.38) at 100 cd/m2 with a color rendering index of 85 are demonstrated. The white emission of the fabricated OLEDs are oriented from the near UV-deep blue emission of Ir(pmb)3 and the successfully controlled exciplex emission, between the Ir(pmb)3-host, and the Ir(pmb)3-interfaced material.     

The characteristics of electroplex generated from the organic light emitting diodes

The color stability and purity from OLED is of current interest. Aggregation of dyes alters the device color after fabrication of the devices. The aggregates can be exciplex and electroplex, which is the excited complex that generated after electrically excited state under high electric field. Comparative study of emission spectra of exciplex and electroplex leads us to conclude that the new electroplex states causes the bathochromic shift of the electroluminescence spectrum from the devices with TPD/PBD layers. The photoluminescence maximum obtained from the TPD/PBD layers of the device was 420 nm, and the electroluminescence maximum obtained from the device became 480 nm. The bathochromic shift cannot be attained with photoluminescence study with highly concentrated TPD/PBD mixture. This clearly indicates that the 480 nm spectrum of the devices is not resulted from the exciplex formation with TPD and PBD. We observed the overshoot in EL spectrum from the OLEDs. The most intense overshoot was observed at 460 nm, which is due to the aggregate that are formed after the electric field has been removed from the devices.     

Red phosphorescent organic light-emitting diodes based on the simple structure

We demonstrated that the simple layered red phosphorescent organic light-emitting diodes (OLEDs) are possible to have high efficiency, low driving voltage, stable roll-off efficiency, and pure emission color without hole injection and transport layers. We fabricated the OLEDs with a structure of ITO/CBP doped with Ir(pq)2(acac)/BPhen/Liq/Al, where the doping concentration of red dopant, Ir(pq)2(acac), was varied from 4% to 20%. As a result, the quantum efficiencies of 13.4, 11.2, 16.7, 10.8 and 9.8% were observed in devices with doping concentrations of 4, 8, 12, 16 and 20%, respectively. Despite of absence of the hole injection and transport layers, these efficiencies are superior to efficiencies of device with hole transporting layer due to direct hole injection from anode to dopant in emission layer.     

Enhanced performance of organic light-emitting diodes by inserting wide-energy-gap interlayer between hole-transport layer and light-emitting layer

We demonstrated that driving voltages, external quantum efficiencies, and power conversion efficiencies of organic light-emitting diodes (OLEDs) are improved by inserting a wide-energy-gap interlayer of (4,4′-N,N′-dicarbazole)biphenyl (CBP) between a hole-transport layer of N,N-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine (α-NPD) and a light-emitting layer of tris(8-hydroxyquinoline)aluminum. By optimization of CBP thicknesses, the device with a 3-nm-thick CBP layer had the lowest driving voltage and the highest power conversion efficiency among the OLEDs. We attributed these improvements to enhancement of a carrier recombination efficiency and suppression of exciton–polaron annihilation. Moreover, we found that the degradation of the OLEDs is caused by decomposition of CBP molecules and excited-state α-NPD molecules.     

Solution processed small molecule-based green phosphorescent organic light-emitting diodes using polymer binder

The authors have demonstrated efficient green organic light-emitting diodes (OLEDs) by using polymer binder. We fabricated small molecular green OLEDs and mixed polymer as a binder such as polystyrene (PS) or poly(N-vinylcarbazole) (PVK). The 4,4'-N,N'-dicarbazole-biphenyl (CBP) is a small molecular material with excellent electrical properties however it become crystalline at high temperature. Polymer binder prevents crystallization of CBP and lead to high efficiency. Therefore, we added PS or PVK into CBP as a polymer binder. As a result, we obtained maximum luminous efficiency, power efficiency and quantum efficiency of 22.8 cd/A, 11.6 Im/W and 6.61% at 23% PS added device.     

High performance inkjet printed phosphorescent organic light emitting diodes based on small molecules commonly used in vacuum processes

High efficiency phosphorescent organic light emitting diodes (OLEDs) are realized by inkjet printing based on small molecules commonly used in vacuum processes in spite of the limitation of the limited solubility. The OLEDs used the inkjet printed 5 wt.% tris(2-phenylpyridine)iridium(III) (Ir(ppy)₃) doped in 4,4′-Bis(carbazol-9-yl)biphenyl (CBP) as the light emitting layer on various small molecule based hole transporting layers, which are widely used in the fabrication of OLEDs by vacuum processes. The OLEDs resulted in the high power and the external quantum efficiencies of 29.9 lm/W and 11.7%, respectively, by inkjet printing the CBP:Ir(ppy)₃ on a 40 nm thick 4,4′,4″-tris(carbazol-9-yl)triphenylamine layer. The performance was very close to a vacuum deposited device with a similar structure.     

Pentafluorophenoxy boron subphthalocyanine as a fluorescent dopant emitter in organic light emitting diodes

A fluorinated phenoxy boron subphthalocyanine (BsubPc) is shown to function as a fluorescent dopant emitter in small molecule organic light emitting diodes (OLEDs). Narrow electroluminescence (EL) emission with a full width at half-maximum of ～30 nm was observed regardless of the host used, indicating that this narrow EL is intrinsic to the BsubPc molecule. A bathochromic shift and the growth of a new EL peak at higher wavelengths with increasing doping concentration were found to be a result of molecular aggregation. Excitation of BsubPc by direct charge trapping as well as Fo?rster resonant energy transfer were shown using different host molecules. A maximum efficiency of 1.5 cd/A was achieved for a 4,4'-N,N'-dicarbazole-biphenyl (CBP) host.     

Study of hole-injecting properties in efficient, stable, and simplified phosphorescent organic light-emitting diodes by impedance spectroscopy

Simplified phosphorescent organic light-emitting diodes (OLEDs) using only two kinds of hosts and comprising either a neat MoO(x) hole-injecting layer (HIL) or a MoO(x)-doped 4,4'-bis(carbazol-9-yl)biphenyl (CBP) HIL were studied. The devices having the MoO(x)-doped CBP HIL are superior to the device having the neat MoO(x) HIL in terms of power efficiency and operational lifetime. Impedance spectroscopy studies revealed that both the reduced hole-injecting barrier height at the anode/doped HIL interface and the reduced bulk resistivity in the doped CBP HIL contribute to the improvement in electroluminescence characteristics. When increasing the MoO(x) volume percentage from 5 to 10% and then to 20%, the hole-injecting barrier height is decreased from 0.63 eV to 0.36 eV and then to 0.18 eV. The power efficiency of the device with a 20 vol % of MoO(x)-doped CBP HIL is more than two times that of the device with a neat MoO(x) HIL measured at a driven current of 5 mA/cm(2). Moreover, the lifetime of the device with a 20 vol % of MoO(x)-doped CBP HIL is more than three times that of the device with a neat MoO(x) HIL estimated at an initial luminance of 1000 cd/m(2). The MoO(x)-doped HIL further ensures the feasibility of the simplified phosphorescent OLEDs for potential applications.     

Purely Organic Thermally Activated Delayed Fluorescence Materials for Organic Light‐Emitting Diodes

The design of thermally activated delayed fluorescence (TADF) materials both as emitters and as hosts is an exploding area of research. The replacement of phosphorescent metal complexes with inexpensive organic compounds in electroluminescent (EL) devices that demonstrate comparable performance metrics is paradigm shifting, as these new materials offer the possibility of developing low‐cost lighting and displays. Here, a comprehensive review of TADF materials is presented, with a focus on linking their optoelectronic behavior with the performance of the organic light‐emitting diode (OLED) and related EL devices. TADF emitters are cross‐compared within specific color ranges, with a focus on blue, green–yellow, orange–red, and white OLEDs. Organic small‐molecule, dendrimer, polymer, and exciplex emitters are all discussed within this review, as is their use as host materials. Correlations are provided between the structure of the TADF materials and their optoelectronic properties. The success of TADF materials has ushered in the next generation of OLEDs.     

Exciplex kinetics in nanocrystal organic light-emitting diodes

We studied the exciplex kinetics in nanocrystal organic light-emitting diodes (NC-OLEDs) where the emissive layer of inorganic nanocrystal quantum dots is sandwiched between the electron and hole transport layers of organic semiconductors at the organic–organic interface. We modeled exciplex generation, diffusion, recombination, and capture by nanocrystals via the Förster mechanism in NC-OLEDs. The exciplex kinetics determines the NC-OLED operation characterized by the quantum yield efficiency and emission intensity and it can be optimized by controlling the nanocrystal separation in the NC-OLED.