PVK:NPB复合空穴传输层对有机电致发光器件的影响

采用poly(N-vinylearbazole)(PVK):N,N'-bis-(1-naphthyl)-N,N'-bipheny-1,1'-biphenyl-4,4'-diamine(NPB)掺杂体系作为复合空穴传输层,通过调节该体系的组分,制备了结构为indium-tin oxide(ITO)/PVK:NPB/8-hydroxyquinoline aluminum(Alq3)/Mg:Ag的双层有机电致发光器件(OLED),研究了具有不同掺杂质量比的OLED器件的电致发光特性,并对掺杂薄膜的表面形貌进行了表征.结果表明,将NPB掺杂到PVK中会提高空穴传输能力,改善器件的发光亮度和效率,并调节载流子复合区域的位置,光谱谱峰从509 nm移动到530 mm;但随着NPB质量比例提高,掺杂薄膜表面的平均粗糙度由3 nm上升为10 mm,电流密度和亮度先升高后降低.当PVK和NPB的掺杂质量比为l:3时,器件具有最优性能,发光亮度达到7852 cd/m2,功率效率为1.75 lm/W.     

空穴传输层厚度对有机发光二极管性能的影响

采用聚乙烯基咔唑(PVK)作为空穴传输层,8-羟基喹啉铝(Alq3)作为发光层,制备了结构为ITO/PVK/Alq3/Mg∶Ag/Al的有机发光二极管(OLED),通过测试器件的电流-电压-发光亮度特性,研究了空穴传输层厚度对OLED器件性能的影响,优化了器件功能层的厚度匹配.实验结果表明,OLED的光电性能与空穴传输层的厚度密切相关,空穴传输层厚度为15nm时,OLED器件具有最低的启亮电压,最高的发光亮度和最大的发光效率.     

利用Alq3掺杂在NPB中制备白光OLED

利用Alq3掺杂在NPB中作为空穴传输层,并以DPVBi和rubrene作为发光层,制备了多层的白光有机发光器件(OLED).与在同一条件下的对比器件相比,掺杂的器件在相同电压下亮度和效率都有所增加.掺杂的器件的最大亮度在17 V时达到了19 921 cd/m2,最大效率在7 V时达到了3.69 cd/A,色坐标(CIE)在5～16 V内几乎没有改变,我们认为,掺杂器件性能的提高是由于掺杂剂Alq3分子对空穴有散射作用,阻挡了部分空穴的传输,降低了空穴的迁移率;而Alq3又是很好的电子传输材料,Alq3掺杂提高了空穴和电子在发光层中的注入平衡,有利于激子的形成,从而提高了器件的性能.     

低温溶液法制备氧化钼及其在QLEDs中的应用

空穴注入层(HIL)在量子点发光二极管(QLEDs)中有重要作用。使用低温溶液法制作了MoOx纳米颗粒,将其在氧化铟锡(ITO)玻璃上旋涂成膜后使用不同温度进行退火处理,并作为空穴注入层进行量子点发光二极管的制作。实验结果表明,氧化钼薄膜有着与ITO玻璃阳极和Poly-TPD空穴传输层匹配的能级,可用作量子点发光二极管的空穴注入层,而使用经100 ℃退火处理后的MoOx薄膜作为空穴注入层的器件性能最佳：器件启亮电压为2.5 V,最高外量子效率为11.6%,在偏压为10 V时,器件的最高亮度达到27 100 cd/m2。     

在NPB中掺杂Alq_3改善有机电致发光器件的性能

在空穴传输层N,N′-diphenyl-N,N′-bis-1-naphthyl-(1,1′-biphenyl)-4,4′-diamine(NPB)中掺杂电子传输材料Aluminium-tris-8-hydroxy-quinoline(Alq3)制备了有机电致发光器件。当掺杂浓度低于5%时器件仍为蓝光发射,但与同等结构没有掺杂的器件相比,蓝光器件的亮度提高了近20%,达到了12460cd/m2,外量子效率提高了15.5%。随着掺杂浓度的增加,光谱发生了从蓝光到绿光的红移,这种掺杂方案能够改善空穴和电子的注入平衡,使得空穴和电子在发光层中能够有效地复合,器件的色度、亮度和效率都有了相应的改变。     

在Liq中掺杂Yb作为电子注入层修饰电极Yb/Al

基于绿光器件ITO/HAT-CN/TAPC/CBP∶Ir(ppy)_3/TmPyPB/Liq/Al,通过在Liq中掺杂不同浓度的Yb作为电子注入层修饰电极,研究Yb不同浓度的掺杂比对器件性能的影响。研究表明,在Liq中掺杂微量的Yb能有效提高器件的光电性能。当Yb的掺杂比为1.85%时,器件性能最好。在0.25mA/cm~2的条件下点亮,启亮电压为3.65V,最高亮度为26 720cd/m~2,最高电流效率为87.07cd/A,最高功率效率为74.89lm/W,最高外量子效率为24.07%。与参考器件对比,其最高亮度提高2 181cd/m~2,最高电流效率提高18.42cd/A,最高功率效率提高10.6lm/W,最高外量子效率提高5.27%。     

基于ADN:TBPe发光层的蓝光OLED器件

全色显示是有机电致发光显示(OLED)器件发展的目标,而高性能蓝色发光器件,也是目前有机电致发光显示研究的热点。以NPB和Alq3分别作为空穴传输层和电子传输层,制作了结构为ITO/CuPc(150nm)/NPB(500nm)/ADN(300nm)∶TBPe(30nm)/Alq3(350nm)/RbF(20nm)/Al(1000nm)的蓝光OLED器件,发光亮度达8600cd/m2,发光效率达2.669cd/A,色坐标(X=0.1315,Y=0.1809)。研究发现ADN∶TBPe发光层体系的引入大大改善了蓝光器件的发光效率和性能。     

基于纳米氧化钛电子传输层的量子点发光二极管器件的制备与研究

为了获得高效而经济的光电器件,采用湿法旋涂技术制备量子点发光二极管器件( QLED),并对其光电特性进行了测试。此器件基于纳米二氧化钛( TiO2)的电子传输层,采用ITO玻璃作为阳极,Al为阴极,PEDOT为空穴注入层,TFB为空穴传输层,量子点( QD)作为发光层的结构。研究发现,QLED器件的开启电压为2.6 V,发光高度大于10 cd/m2。实验结果说明了TiO2可以作为获得高效QLED器件以及其他光电器件的一种有效途径。     

基于空间电荷限制电流模型的FeCl3掺杂CBP的空穴迁移率研究

基于不同浓度FeCl3掺杂的4,4′-N,N′-二咔唑基联苯(CBP)设计制作了一系列的单空穴有机电致发光器件(OLED),采用空间电荷限制电流法估算了具有不同浓度FeCl3掺杂的CBP的空穴迁移率,并与OLED中常用的空穴传输材料N,N′-二苯基-N,N′-(1-萘基)-1,1′-联苯-4,4′-二胺(NPB)进行了比较研究。结果表明,FeCl3掺杂CBP可以极大地提高CBP薄膜的空穴迁移率,当FeCl3的浓度为12%时空穴迁移率最大,在电场强度为0.5MV/cm的条件下迁移率为4.5×10-5cm2/V·s,即使在零电场条件下迁移率依然高达2.2×10-5 cm2/V·s,近似为常用空穴传输材料NPB空穴迁移率的4倍。用CBP∶12%FeCl3做空穴传输层,制备了OLED器件,最大亮度为68468cd/m2,相对于采用NPB做空穴传输层的参比器件提高了97%,最大电流效率为31.28cd/A,比参比器件提高了23%。器件亮度和效率的提高归因于空穴传输性能的改善,使得器件中载流子的传输更为平衡,从而提高了激子形成的几率,且减少了激子-极化子之间的淬灭。     

利用ZnCl2原位钝化电子传输层提高量子点发光二极管性能

在量子点发光二极管(QLED)中,电子-空穴注入不平衡和量子点层/电子传输层间界面的荧光猝灭限制着QLED效率的提升。基于此,采用金属卤化物(ZnCl₂)原位处理电子传输层方法来减少氧化锌(ZnO)电子传输层的氧空位,同时有效钝化其表面不饱和键,因此在一定程度上实现抑制量子点/电子传输层界面的荧光猝灭和提高QLED中的电子-空穴注入平衡的目的,最终得到了高亮度、高效率的QLED。原位钝化处理后的ZnO基QLED的最大亮度、峰值电流效率、峰值功率效率和峰值外量子效率(EQE)分别从未处理QLED的176 800 cd/m²、9.86 cd/A、8.38 lm/W和7.42%提高到219 200 cd/m²、15.14 cd/A、12.66 lm/W和11.65%。结果表明,ZnCl₂原位钝化ZnO电子传输层对QLED性能的提升起到重要的作用。     

Highly efficient all-solution processed blue quantum dot light-emitting diodes based on balanced charge injection achieved by double hole transport layers

Solution-processed blue quantum dot light-emitting diodes (QLEDs) suffer from low device efficiency, whereas the balance of electron and hole injection is critical for obtaining high efficiency. Herein, synergistical double hole transport layers (D-HTLs) are employed, which use poly(9-vinylcarbazole) (PVK) stacked on poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-butylphenyl) (TFB). The fabrication of D-HTLs is achieved by using dimethyl formamide (DMF) as the solvent for PVK, with which the underlying TFB layer almost remains unwashed and undamaged during the spin-coating process of PVK layer. TFB/PVK D-HTLs form the stepwise energy level for hole injection, which reduces the hole injection barrier and favors the carrier balance in the emission layer (EML). The optimized blue QLED with TFB/PVK D-HTLs shows a maximum external quantum efficiency (EQE) of 13.7%, which is 3-fold enhancement compared to that of the control device with single TFB HTL. The enhancement of the QLED performance can be attributed to the improvement of surface morphology and charge injection balance for the stepwise D-HTLs based QLEDs. This work manifests the positive effect on performance boost by selecting appropriate solvents towards stepwise D-HTLs formation and paves the way to fabricate highly efficient all-solution processed light emitting diodes.     

Boosting the performance of solution-processed quantum dots light-emitting diodes by a hybrid emissive layer via doping small molecule hole transport materials into quantum dots

Solution-processed colloidal quantum dot light-emitting diodes (QLED) have attracted many attentions with significant progress in recent years. However, QLED devices still face some challenges. The energy barrier between Cd-base quantum dots (QDs) and commonly used hole transport materials is larger than that between QDs and electron transport materials, which leads to the imbalance of carriers in the light emitting layer (EML) and the low performance of QLED devices. Herein, we report a simple strategy to improve the device performance by doping small molecule transport material 4,4′-cyclohexylidenebis[N,N-bis(p-tolyl)aniline] (TAPC) into red CdSe/ZnS QDs. The optimized red QLED devices with TAPC-doped emissive layer at a ratio of 3.2 wt% achieve 20.0 cd/A of maximum current efficiency, 16.6 lm/W of power efficiency and 15.7% of external quantum efficiency, which is 30%, 58% and 33% higher than the control device. The improved performance of devices can be ascribed to the increase of hole current density, decrease of leakage electrons and more balanced quantity of carriers in EML. This work put forward a viewpoint to improve the performance of QLED devices via doping high hole mobility materials into emission layer.     

Optimization of carrier transport layer: A simple but effective approach toward achieving high efficiency all-solution processed InP quantum dot light emitting diodes

High performance quantum dot light emitting diodes (QD-LED) are being considered as a next-generation technology for energy efficient solid-state lighting and displays. In recent years, cadmium (Cd)-based QLEDs have made great progress in performance, which is close to commercial applications. However, the performance of environmentally friendly Cd-free QD-LED still needs to be improved. In this letter, using InP/ZnS quantum dots (QDs), an environmentally friendly red QDs material, as the light emitting layer, low-cost all-solution processed red InP/ZnS QD-LED are fabricated. The optimized device with a hybrid multilayered structure employing an organic double hole transport layer (HTL) with doping small molecules (TFB/PVK:TAPC) and an inorganic ZnMgO nanoparticles (NPs) electron transport layer (ETL), here TFB, PVK and TAPC represent poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(p-butylphenyl))-diphenylamine)], poly (9-vinlycarbazole) and 1,1-bis [4-[N,N′-di (p-tolyl)amino]phenyl]-cyclohexane, respectively. The best device exhibits a peak current efficiency (CE) of 7.58 cd A⁻¹, which is 2.4 times higher than the control device using PVK (HTL) and ZnO (ETL). At the same time, turn-on voltage dropped from 2.8 V (control devices) to 2.4 V. These superb QD-LED performances originate not only from the improved hole injection by the introduction of a double hole layer and the reduced the quenching of excitons by using ZnMgO NPs ETL but also from increasing the hole mobility with doping of small molecule materials in PVK to balance the carrier transportation. This work provides a simple and feasible idea with optimization the carrier transport for realizing high-efficiency QD-LED devices.     

Controlling charge balance using non-conjugated polymer interlayer in quantum dot light-emitting diodes

The balance of electron–hole charge carriers in quantum dot (QD) light-emitting diodes (QLEDs) is an important factor to achieve high efficiency. However, poor interfacial properties between QDs and their adjacent layers are likely to deteriorate the electron–hole charge balance, resulting in the poor performance of a QLED. In this paper, we report an enhanced efficiency in red-emitting inverted QLEDs by modifying the interface properties between QDs and ZnO electron transport layer (ETL) using a thin layer of non-conjugated polymer, poly(4-vinylpyridine) (PVPy). Based on the precise control of the electrical properties with PVPy, the maximum efficiency of the QLED is enhanced by 30% compared to the device without a PVPy layer. In particular, the efficiency at low current density region is significantly increased. We investigate the effect of the PVPy interlayer on the performance of QLEDs and find that this thin layer not only shifts the energy levels of the underlying ZnO ETL, but also effectively blocks the leakage current at the ETL/QD interface.     

Improved performance of CdSe/ZnS quantum dot light-emitting diodes through doping with small molecule CBP

The poor film formation of CdSe/ZnS quantum dots (QDs) during spin-coating makes a substantial impact on the device performance of quantum dot light-emitting diodes (QLEDs). This work proposes a method to improve the morphology of the quantum dot light-emitting layer (EML) by adding small organic molecular 4,4''-Bis(9H-carbazol-9-yl) biphenyl (CBP) into the layer. Its surface roughness reduces from 6.21 nm to 2.71 nm, which guarantees a good contact between hole transport layer (HTL) and EML. Consequently, the CdSe/ZnS QDs:CBP based QLED achieves maximum external quantum efficiency (EQE) of 5.86%, and maximum brightness of 10 363 cd/m2. It is demonstrated that the additive of small organic molecules could be an effective way to improve the brightness and the efficiency of QLEDs.     

High-performance azure blue quantum dot light-emitting diodes via doping PVK in emitting layer

Highly bright and efficient azure blue quantum dot-based light-emitting diodes (QD-LEDs) have been demonstrated by employing ZnCdSe core/multishell QDs as emitters and the crucial development we report here is the ability to dramatically enhance the efficiency and brightness through doping poly vinyl(N-carbazole) (PVK) in the emissive layer to balance the charge injection. The best device displays remarkable features like maximum luminance of 13,800 cd/m², luminous efficiency of 6.41 cd/A, and external quantum efficiency (EQE) of 8.76%, without detectable red-shift and broadening in electroluminescence (EL) spectra with increasing voltage as well as good spectral matching between photoluminescence (PL) and EL. Such azure blue quantum-dot LEDs show a 140% increase in external quantum efficiency compared with QD-LEDs without PVK. More important, the peak efficiency of the QD-LEDs with PVK dopant is achieved at luminance of about 1000 cd/m², and high efficiency (EQE > 8%) can be maintained with brightness ranging from 200 to 2400 cd/m². There are two main aspects of the role of PVK in the proposed system. Firstly, the lower HOMO of PVK than (poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) can reduce the potential barrier for 0.4 eV at the interface of QDs and hole transport layer which could result in higher hole injection efficiency along with good EQE as compared to TFB-only HTLs. Secondly, with PVK acting as buffer layer of TFB and QDs, the exciton energy transfer from the organic host to the QDs can be effectively improved.     

Cadmium-free quantum dots based violet light-emitting diodes: High-efficiency and brightness via optimization of organic hole transport layers

Bright and efficient violet quantum dot (QD) based light-emitting diodes (QD-LEDs) with heavy-metal-free ZnSe/ZnS have been demonstrated by choosing different hole transport layers, including poly(4-butyl-phenyl-diphenyl-amine) (poly-TPD), poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB), and poly-N-vinylcarbazole (PVK). Violet QD-LEDs with maximum luminance of about 930 cd/m², the maximum current efficiency of 0.18 cd/A, and the peak EQE of 1.02% when poly-TPD was used as HTL. Higher brightness and low turn-on voltage (3.8 V) violet QD-LEDs could be fabricated when TFB was used as hole transport material. Although the maximum luminance could reach up to 2691 cd/m², the devices exhibited only low current efficiency (∼0.51 cd/A) and EQE (∼2.88%). If PVK is used as hole transport material, highly efficient violet QD-LEDs can be fabricated with lower maximum luminance and higher turn-on voltages compared with counterpart using TFB. Therefore, TFB and PVK mixture in a certain proportion has been used as HTL, turn-on voltage, brightness, and efficiency all have been improved greatly. The QD-LEDs is fabricated with 7.39% of EQE and 2856 cd/m² of maximum brightness with narrow FWHM less than 21 nm. These results represent significant improvements in the performance of heavy-metal-free violet QD-LEDs in terms of efficiency, brightness, and color purity.     

载流子平衡方法提高量子点发光二极管效率的研究

尝试采用三种方式来平衡载流子的浓度,以提高量子点发光二极管(QLED)的外量子效率等性能:在正装结构(ITO/HIL/HTL/QD/ETL/EIL/金属阴极)的QLED的发光层和电子传输层中间插入超薄聚甲基丙烯酸甲脂(PMMA)电子阻挡层;在空穴注入和传输层方面,通过使用更加优化的HIL等来提高空穴注入和传输几率;在QD发光层方面,用短链配体来置换量子点的长链配体以增加载流子向量子点发光层中的传输效率等。在进行量子点配体交换的同时带来了量子点在正交溶剂中的可溶性优势,有利于QLED器件的全溶液法制备。     

量子点发光器件的制备与仿真分析

为研究量子点发光器件结构与性能的关系,制备了以CdSe/ZnS量子点作为发光层、poly-TPD作为空穴传输层,Alq3作为电子传输层的量子点发光二极管,对器件结构及性能参数进行了表征,结果显示器件具有开启电压低、色纯度高等特点.结合测试数据,对量子点发光二极管进行了器件结构建模,利用隧穿模型及空间电荷限制电流模型对实验结果进行了分析,研究了器件中载流子的注入与传输机理.器件测试与仿真结果表明:各功能层厚度会影响载流子在量子点层的注入平衡,同时器件中载流子的注入与传输存在一转变电压,当外加电压低于转变电压时,器件中载流子的注入主要符合隧穿模型;当外加电压高于转变电压时,器件中载流子的注入主要符合空间电荷限制电流模型.研究结果验证了器件结构建模的合理性,可以利用仿真的方法进行器件结构优化并确定相关参数,这对器件性能的提高具有指导意义.