White organic light-emitting diodes using a quantum dot as a color changing material

White organic light-emitting diodes (WOLEDs) were fabricated by using a blue emitting layer combined with quantum dot (QD) based color converting materials. Orange emitting QD was used as a color converting material and effective color conversion was realized. A white color coordinate of (0.32, 0.41) was obtained with a current efficiency of 8.3 cd/A at 1000 cd/m².     

双极性材料在有机太阳能电池领域的应用

双极性材料以其低能隙、宽吸收、高电子传导率和较高稳定性的优势成为增强有机太阳能电池性能的优良材料。研究显示,双极性材料不但能够作为有机光伏器件中的给体材料和受体材料,还能作为辅助添加剂来增加电池的能量转化效率。     

Highly efficient blue organic light-emitting diodes using quantum well-like multiple emissive layer structure

In this study, the properties of blue organic light-emitting diodes (OLEDs), employing quantum well-like structure (QWS) that includes four different blue emissive materials of 4,4′-bis(2,2′-diphenylyinyl)-1,1′-biphenyl (DPVBi), 9,10-di(naphth-2-yl)anthracene (ADN), 2-(N,N-diphenyl-amino)-6-[4-(N,N-diphenyl amine)styryl]naphthalene (DPASN), and bis(2-methyl-8-quinolinolate)-4-(phenyl phenolato) aluminum (BAlq), were investigated. Conventional QWS blue OLEDs composed of multiple emissive layers and charge blocking layer with lower highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy level, and devices with triple emissive layers for more significant hole-electron recombination and a wider region for exciton generation were designed. The properties of triple emissive layered blue OLEDs with the structure of indium tin oxide (ITO) /N,N′-diphenyl-N,N′-bis(1-naphthyl-phenyl)-(1,1′-biphenyl)-4,4′-diamine (NPB) (700 Ǻ)/X (100 Ǻ)/BAlq (100 Ǻ)/X (100 Ǻ)/4,7-diphenyl-1,10-phenanthroline (Bphen) (300 Ǻ)/lithium quinolate (Liq) (20 Ǻ)/aluminum (Al) (1,200 Ǻ) (X = DPVBi, ADN, DPASN) were examined. HOMO-LUMO energy levels of DPVBi, ADN, DPASN, and BAlq are 2.8 to 5.9, 2.6 to 5.6, 2.3 to 5.2, and 2.9 to 5.9 eV, respectively. The OLEDs with DPASN/BAlq/DPASN QWS with maximum luminous efficiency of 5.32 cd/A was achieved at 3.5 V.     

Blue organic light-emitting diodes using novel spiro[fluorene-benzofluorene]-type host materials

Deep blue colored, fluorescent, spiro-type host materials, 5-[4-(1-naphthyl)phenyl]-spiro[fluorene-7,9′-benzofluorene] and 5,9-bis[4-(1-naphthyl)phenyl]-spiro[fluorene-7,9′-benzofluorene] were designed and successfully prepared by the Suzuki reaction. The electroluminescence characteristics of the two compounds as blue host materials doped with blue dopant materials, diphenyl[4-(2-[1,1;4,1]terphenyl-4-yl-vinyl)phenyl]amine and 1,6-bis[(p-trimethylsilylphenyl)amino]pyrene (SPP) were evaluated. The device used comprised ITO/N,N′-bis-[4-(di-m-tolylamino)phenyl]-N,N′-diphenylbiphenyl-4,4′-diamine)/bis[N-(1-naphthyl)-N-phenyl]benzidine/Host:5% dopant/tris(8-hydroxyquinolinato)aluminium/Al–LiF. The device obtained from 5-[4-(1-naphthyl)phenyl]-spiro[fluorene-7,9′-benzofluorene] doped with 1,6-bis[(p-trimethylsilylphenyl)amino]pyrene displayed high color purity (0.138, 0.138) and high efficiency (3.70 cd/A at 7 V).     

Electrospray deposition of polymer thin films for organic light-emitting diodes

Electrospray process was developed for organic layer deposition onto polymer organic light-emitting diode [PLED] devices in this work. An electrospray can be used to produce nanometer-scale thin films by electric repulsion of microscale fine droplets. PLED devices made by an electrospray process were compared with spin-coated ones. The PLED device fabricated by the electrospray process showed maximum current efficiency of 24 cd/A, which was comparable with that of the spin-coating process. The electrospray process required a higher concentration of hole and electron transport materials in the inks than spin-coating processes to achieve PLED maximum performance. Photoluminescence [PL] at 407 nm was observed using electrosprayed poly(N-vinyl carbazole) films, whereas a peak at 410 nm was observed with the spin-coated ones. Similar difference in peak position was observed between aromatic and nonaromatic solvents in the spin-coating process. PLED devices made by the electrospray process showed lower current density than that of spin-coated ones. The PL peak shift and reduced current of electrosprayed films can therefore be attributed to the conformation of the polymer.     

High luminance organic light-emitting diodes with efficient multi-walled carbon nanotube hole injectors

We report on high luminance organic light-emitting diodes using acid functionalized multi-walled carbon nanotube (o-MWCNTs) as efficient hole injector electrodes, using a simple, solution processable device structure. At only 10 V, the luminance approaches 50,000 cd/m² with an external quantum efficiency over 2% and a current efficiency greater than 21 cd/A. The investigation of hole-only devices shows that the mechanism for hole injection changes from injection limited to bulk limited because of the higher effective work function of the anode modified by the o-MWCNTs. We expect the enhancement of the local electric field, brought about by both the dielectric inhomogeneities within the o-MWCNT containing anode and the high aspect ratio carbon nanotubes, improves hole injection from the anode to the organic active layer at much lower applied voltage.     

Fabrication of red, green, and blue organic light-emitting diodes using m-MTDATA as a common hole-injection layer

Organic light-emitting diodes (OLEDs) of metal-semiconductor-metal (MSM) structure have been fabricated by using m-MTDATA [4,4′,4′’-tris (3-methylphenylphenylamino) triphenylamine] as a hole-injection layer (HIL). The m-MTDATA is shown to be an effective hole-injecting material for the OLED, in that the insertion of m-MTDATA greatly reduces the roughness of anode surface, lowers the turn-on voltage, and increases the luminous efficiency. Red, green and blue OLEDs were fabricated, and their color coordinates in CIE chromaticity were found to be (0.600, 0.389), (0.240, 0.525) and (0.171, 0.171), respectively. The luminous efficiencies of the fabricated OLEDs were 1.4 lm/W at 106 cd/m² for red, 1.4 lm/W at 100 cd/m² for green, and 2.0 lm/W at 104 cd/m² for blue.     

Lifetime study of red phosphorescent organic light-emitting diodes with a double doping structure

The lifetime of red phosphorescent organic light-emitting diodes with a double doping structure was studied. Green and red phosphorescent dopants were co-doped in the emitting layer and the lifetime of the red devices with the doubly doped emitting structure was dependent on the doping concentration of the green dopant due to the energy transfer from the green dopant to the red dopant.     

Origin of bistable memory characteristics of organic light-emitting diodes with LiF/Al cathode

Bistable memory performances of organic light-emitting diodes (OLEDs) with LiF/Al cathode were investigated and the origin of bistability was studied. LiF was essential to get stable memory performances in OLEDs and on/off ratio was improved by more than 50 times by using LiF/Al instead of Al cathode. High on/off ratio over 1000 was obtained from switching test and the multilevel switching of organic light-emitting bistable devices (OLEBDs) was realized by changing the writing voltage of OLEBDs. AlF₃ formation at the interface during evaporation of Al was proposed as the main mechanism for bistability of OLEBDs.     

Recombination zone study of phosphorescent organic light-emitting diodes with triplet mixed host emitting structure

Recombination zone of green phosphorescent organic light-emitting diodes (PHOLEDs) with triplet mixed host was studied using red sensing layer. Recombination zone of triplet mixed host device with 4,4′,4″-tris(N-carbazolyl)triphenylamine and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene as hosts was rather dispersed compared with that of single host device with recombination zone near charge transport layer. The recombination zone was shifted to hole transport side at high driving voltage.     

The influence of type-I and type-II triplet multiple quantum well structure on white organic light-emitting diodes

We demonstrate high-efficient white organic light-emitting diodes (WOLEDs) based on triplet multiple quantum well (MQW) structure and focus on the influence on WOLEDs through employing different potential barrier materials to form type-I and type-II MQWs, respectively. It is found that type-I MQW structure WOLEDs based on 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene as potential barrier layer (PBL) offers high electroluminescent (EL) performance. That is to say, maximum current efficiency and power efficiency are achieved at about 1,000 cd/m² with 16.4 cd/A and 8.3 lm/W, which increase by 53.3% and 50.9% over traditional three-layer structure WOLEDs, respectively, and a maximum luminance of 17,700 cd/m² is earned simultaneously. The achievement of high EL performance would be attributed to uniform distribution and better confinement of carriers within the emitting layer (EML). However, when 4,7-diphenyl-1,10-phenanthroline or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used as PBL to form type-II MQW structure, poor EL performance is obtained. We attribute that to improper energy level alignment between the interface of EML/PBL, which leads to incomplete confinement and low recombination efficiency of carriers, a more detailed mechanism was argued.     

绿色有机电致发光材料C545T合成工艺研究

研究了绿色有机电致发光材料C545T的合成工艺。以价格较便宜的1-溴-3-甲基-2-丁烯代替1-氯-3-甲基-2-丁烯,降低了原料价格,提高了产品收率;其次,中间体2-苯并噻唑乙酸乙酯的合成采用微波法代替传统的加热反应法,缩短了反应时间,提高了产品收率;另外,最后一步的Knovenagel反应采用有机碱哌啶作催化剂,也缩短了反应时间,提高了产品收率。该合成工艺生产周期短,反应条件温和,纯化过程简单,合成成本低,六步合成总收率达8.2%,产品纯度达99.9%。     

Novel carbazole/pyridine-based host material for solution-processed blue phosphorescent organic light-emitting devices

3,6-Bis(3,5-di(pyridin-3-yl)phenyl)-9-phenyl-9H-carbazole, a novel host material for solution-processed blue phosphorescent organic light-emitting devices was synthesized by a Suzuki coupling reaction. The optical, electrochemical and thermal properties of this novel crabazole have been characterized. The compound exhibits a high glass-transition temperature (Tg = 161 °C) and high triplet energy (E_T = 2.76 eV). Additionally, atomic force microscopy measurements indicate that high-quality amorphous films of this novel compound can be prepared by spin-coating. Solution-processed blue phosphorescent organic light-emitting devices were obtained using the carbazole as the host material for the phosphorescence emitter iridium(III) bis(4,6-difluorophenylpyridinato)- picolinate and their electroluminescence properties were evaluated.     

Effect of triplet multiple quantum well structures on the performance of blue phosphorescent organic light-emitting diodes

We investigate multiple quantum well [MQW] structures with charge control layers [CCLs] to produce highly efficient blue phosphorescent organic light-emitting diodes [PHOLEDs]. Four types of devices from one to four quantum wells are fabricated following the number of CCLs which are mixed p- and n-type materials, maintaining the thickness of the emitting layer [EML]. Remarkably, such PHOLED with an optimized triplet MQW structure achieves maximum luminous and external quantum efficiency values of 19.95 cd/A and 10.05%, respectively. We attribute this improvement to the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation which occurs within each EML. It also shows a reduction in the turn-on voltage from 3.5 V (reference device) to 2.5 V by the bipolar property of the CCLs.     

有机相微波合成AgInS2量子点及其白光发光二极管应用研究

AgInS₂量子点(AIS QDs)由于具有绿色环保、发射波长可调、荧光寿命长、斯托克斯位移大等优势,在光电和生物医药领域具有广阔的应用前景。采用微波辅助加热法在十八烯溶剂中制备了AIS QDs。通过X射线衍射、透射电子显微镜、光致发光光谱系统研究了反应时间对AIS QDs的物相、形貌及荧光性能的影响,采用傅里叶红外光谱和X射线光电子能谱表征了量子点表面结合的情况。实验结果表明：当微波功率为800 W、反应时间为5~25 min时均可以制备出AIS QDs。随着反应时间的延长,AIS QDs的粒径由3 nm增加至4 nm,发光峰位在592.0~619.6 nm范围内调谐;同时AIS QDs的荧光强度逐渐提高,并在15 min达到峰值,量子产率(PLQY)达到16.16%。进一步采用ZnS作为包覆壳层有效钝化量子点表面缺陷、提高荧光性能,制备出的AIS@ZnS QDs的PLQY增加至31.21%。将AIS@ZnS QDs和商用荧光粉共同作为发光层制备成白光发光二极管(WLED)器件,在20 mA电流驱动下发光效率(LE)为74.90 lm/W,显色指数(CRI)和色温(CCT)分别为83.31和3823 K,表明制备的量子点在固态照明领域具有潜在的应用前景。     

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.     

Electronic structures and photophysical properties of carbazole- and thiophene-based organic compounds used as hole-injecting layer for organic light-emitting diodes (OLEDs)

In this study, we have carried out a theoretical study on six organic compounds based on thiophene and carbazole, with the aim of using them as a hole-injecting layer of organic light-emitting diodes (OLEDs). In this study, we have tested two types of structures: D-π-D for MO1, MO2, MO3, and MO4 compounds and D-π-A for MO5 and MO6 compounds. The correlation structure-properties of these studied compounds have been proceeded and discussed by analyzing highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy gap, polarization effect, atom transition density matrix, absorption, and photoluminescence (PL). This theoretical study, based on density functional theory (DFT)/TPSSTPSS/aug-cc-pVQZ and the integral-equation-formalism polarizable continuum model/Coulomb attenuated method-Becke, 3-parameter, Lee–Yang–Parr (IEFPCM/TD-CAM-B3LYP)/6-31++G(d,p) is consolidated by experimental data for MO1, MO2, and MO4 compounds, allowing the determination of their structural and optoelectronic properties (HOMO, LUMO, gap [Eg], absorption, and emission parameters). The obtained results appear very conclusive and show that the performance of these compounds in terms of luminescence, absorption, and current–voltage (I–V) characteristics of OLED devices make them a promising candidate for the realization of light-emitting diodes.     

The synthesis,characterization and electroluminescent properties of zinc(II) complexes for single-layer organic light-emitting diodes

(E)-2-(2-(9-p-tolyl-9H-carbazol-3-yl)vinyl)-8-hydroxyl-quinoline, (E)-2-(2-(9-(4-methoxyphenyl)-9H-carbazol-3-yl)vinyl)-8-hydroxyquinoline and their respective zinc(II) complexes were synthesized and their structures confirmed using UV–vis, FT-IR, ESI-MS, FAB-MS, ¹H NMR and elemental analysis. The two Zn(II) complexes displayed high thermal stability with thermal decomposition temperatures of 422 °C and 410 °C, respectively. Photoluminescence spectra revealed that the complexes possessed maximum emissions at 575 and 570 nm, respectively, in the green region. Single-layer, organic light-emitting diodes built using these complexes emitted yellow light, as a result of a red-shift, with maximum luminances of 489 cd/m² and 402 cd/m² as well as luminance efficiencies of 0.41 cd A^?1 and 1.81 cd A^?1, respectively.