About the transparent electrode of the organic photovoltaic cells

Electrodes and the nature of their contact with organic materials play a crucial role in the realization of efficient optoelectronic components. Whether the injection (organic light-emitting diodes - OLEDs) or collection (organic photovoltaic cells - OPV cells) of carriers, contacts must be as efficient as possible. To do this, it is customary to refer to electrode surface treatment and/or using a buffer layer all things to optimize the contact. Efficiency of organic photovoltaic cells based on organic electron donor/organic electron acceptor junctions can be strongly improved when the transparent conductive anode is coated with a buffer layer (ABL). We show that an ultra-thin gold (0.5 nm) or a thin molybdenum oxide (3-5 nm) can be used as efficient ABL. However, the effects of these ABL depend on the highest occupied molecular orbital (HOMO) of different electron donors of the OPV cells. The results indicate that, in the case of metal ABL, a good matching between the work function of the anode and the highest occupied molecular orbital of the donor material is the major factor limiting the hole transfer efficiency. Indeed, gold is efficient as ABL only when the HOMO of the organic donor is close to its work function Phi(Au). MoO3 has a wider field of application as ABL than gold. The role of the oxide is not so clearly understood than that of Au, different models proposed to interpret the experimental results are discussed.

Effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes

In this paper we present the effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes (OLEDs). A number of OLED devices have been fabricated with combinations of hole injecting and hole blocking layers of varying thicknesses. Even though hole blocking and hole injection layers have opposite functions, yet there is a particular combination of their thicknesses when they function in conjunction and luminous efficiency and power efficiency are maximized. The optimum thickness of CuPc (Copper(II) phthalocyanine) layer, used as hole injection layer and BCP (2,9 dimethyl-4,7-diphenyl-1,10-phenanthroline) used as hole blocking layer were found to be 18 nm and 10 nm respectively. It is with this delicate adjustment of thicknesses, charge balancing is achieved and luminous efficiency and power efficiency were optimized. The maximum luminous efficiency of 3.82 cd/A at a current density of 24.45 mA/cm(2) and maximum power efficiency of 2.61 lm/W at a current density of 5.3 mA/cm(2) were achieved. We obtained luminance of 5993 cd/m(2) when current density was 140 mA/cm(2). The EL spectra was obtained for the LEDs and found that it has a peaking at 524 nm of wavelength. (C) 2012 Elsevier B.V. All rights reserved.

Organic white-light emitting materials

Full-color emissive organic materials have attracted significant attention in recent years as key components in display and lighting devices based on OLEDs. An ideal white-light emitter demands simultaneous emission of red, green and blue with nearly similar distribution of intensities covering the entire region of visible spectra. However, the design of such white-light emitters is not straightforward. Mixing several emitters is seldom successful owing to the negative effects of intermolecular interactions and energy transfer processes. Nonetheless, these fundamental questions have been addressed in recent times by several research groups of vastly different expertise leading to a considerable progress in the field of organic white-light emitters. The designs cover a large area of the chemistry ranging from frustrated energy transfer to simple protonation or from designed self-assembly to simple mixing of materials. In this review, the concepts and rational approaches underlying the design of white-light emissive organic materials are described. (C) 2014 Elsevier Ltd. All rights reserved.

High T-g fluoranthene-based electron transport materials for organic light-emitting diodes

In this study, fluoranthene-based derivatives with a high thermal stability were synthesized for applications in organic electroluminescent devices. The two derivatives synthesized in this study, bis(4-(7,9,10-triphenylfluoranthen-8-yl)phenyl)sulfane (TPFDPS) and 2,8-bis(7,9,10-triphenylfluoranthen-8-yl)dibenzob,d]thiophene (TPFDBT), were characterized by cyclic voltammetry, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). TPFDPS exhibits a high T-g of 210 degrees C while TPFDBT is crystalline in nature. Both the derivatives are thermally stable up to 500 degrees C. The charge transport studies reveal predominant electron transport properties. Subsequently, we fabricated blue OLEDs with 2-tert-butyl-9,10-bis-(beta-naphthyl)-anthracene (TBADN) as the emitting layer to demonstrate the applications of these molecules as an electron transporting layer.

Boron clusters in luminescent materials

In recent times, luminescent materials with tunable emission properties have found applications in almost all aspects of modern material sciences. Any discussion on the recent developments in luminescent materials would be incomplete if one does not account for the versatile photophysical features of boron containing compounds. Apart from triarylboranes and tetra-coordinate borate dyes, luminescent materials consisting of boron clusters have also found immense interest in recent times. Recent studies have unveiled the opportunities hidden within boranes, carboranes and metalloboranes, etc. as active constituents of luminescent materials. From simple illustrations of luminescence, to advanced applications in LASERs, OLEDs and bioimaging, etc., the unique features of such compounds and their promising versatility have already been established. In this review, recent revelations about the excellent photophysical properties of such materials are discussed.

输运层厚度与迁移率对双层有机发光器件性能的影响

基于一些合理假设与近似，建立了具有欧姆接触载流子注入的双层有机电致发光器件的解析模型．模型中计算参数只有空穴和电子输运层的厚度、迁移率、外加电压及材料参数Fh和Fe，且这些参数都是可以通过测量得到的．研究了材料参数Fh，Fe对器件复合电流密度的影响及空穴输运层厚度和载流子迁移率对器件电场强度和复合电流密度的影响．结果表明：空穴输运层厚度和载流子迁移率引起电场强度的重新分布，进而对复合电流密度产生影响；接触限制电极注入少数载流子的器件可以取得比欧姆接触注入多数载流子的器件更高的复合电流．

Efficiency improvement of organic light-emitting diodes using 8-hydroxy-quinolinato lithium as an electron injection layer

Organic light-emitting diodes (OLEDs) using tris-(8-hydroxy-quinolinato) aluminum (Alq(3)) as an emitter, 8-hydroxy-quinolinato lithium (Liq) as an electron injection layer, were prepared. Experimental results show that the efficiency of device with Liq is three times higher than that without Liq. The device using Liq as an injection layer is less sensitive in efficiency to the Liq thickness than that using LiF. In addition to the Alq3 based devices, Liq is also very effective as an electron injection layer for 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl based blue OLED and poly (2-methoxy,5-(2-ethyl-hexyloxy)-1,4-phenylenevinylene) based orange polymer OLED. (c) 2004 Elsevier B.V. All rights reserved.

Highly efficient and stable organic light-emitting diodes employing MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride as hole injection layer

We report highly efficient and stable organic light-emitting diodes (OLEDs) with MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride (PTCDA) as hole injection layer (HIL). A green OLED with structure of ITO/20 wt% MoO3: PTCDA/NPB/Alq(3)/LiF/Al shows a long lifetime of 1012 h at the initial luminance of 2000 cd/m(2), which is 1.3 times more stable than that of the device with MoO3 as HIL. The current efficiency of 4.7 cd/A and power efficiency of 3.7 lm/W at about 100 cd/m(2) have been obtained. The charge transfer complex between PTCDA and MoO3 plays a decisive role in improving the performance of OLEDs.

Tandem organic light-emitting diodes with an effective charge-generation connection structure

The tandem organic light-emitting diodes (OLEDs) with an effective charge-generation connection structure of Mg-doped tris(8-hydroxyquinoline) aluminum (Alq(3))/Molybdenum oxide (MoO3)-doped 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) were presented. At a current density of 50 mA/cm(2), the current efficiency of the tandem OLED with two standard NPB/Alq(3) emitting units is 4.2 cd/A, which is 1.7 times greater than that of the single EL device. The tandem OLED with the similar connection structure of Mg-doped PTCDA/MoO3-doped PTCDA was also fabricated and the influences of the different connection units on the current efficiency of the tandem OLED were discussed as well.

铕铽铝配合物及吡唑啉衍生物的电致发光研究

有机电致发光器件（organiclight-emittingdiodes,OLEDs）由于具有全色、低压直流驱动、视角广、高效率、发光颜色丰富等优点,在平板大面积显示领域具有广阔的应用前景,已引起广泛的重视.至目前为止,各式各样多层结构的器件、新的电致发光功能材料在深入研究,各种发光颜色甚至全色器件都已经相继报道.探索新材料,优化器件结构是目前电致发光研究的主要课题.该文主要包括以下几方面工作：（1）稀土配合物真空蒸镀所成膜的形态结构;（2）稀土配合物中第二配体的引入对稀土配合物电致发光性能的影响;（3）稀土配合物溶解性的改善;（4）铝配合物与聚合物PVK基激复合物对电致发光器件性能的影响及基激复合物的证实;（5）高效吡唑啉生物的合成及其电致发光器件的设计.通过深入系统的研究,取得了创新性的结果.

稀土配合物光致发光和电致发光性能的研究

有机电致发光器件(organic light-emitting diodes, OLEDs)由于具有全色、低压直流驱动、视角广、高效率和易于制备大屏幕等优点，在平板显示领域具有广阔的应用前景，已引起世界范围内科技界和企业界的广泛重视。稀土配合物作为发光及载流子传输层材料，具有窄带发射和发射波长分布范围广的特点，有利于实现高的色纯度。然而，有机电致发光的机理还未完全弄清楚，稀土配合物电致发光器件距离实际应用还比较远，需要进一步进行研究。本论文研究了Tb~(3+)、Eu~(3+), Sm~(3+)配合物的光致发光和电致发光性质，制备了绿色、红色和橙色电致发光器件，并对稀土配合物的电致发光机理进行了探讨。对于试配合物，以acac为第一配体，研究了第二配体AAP和bath对配合物和器件发光性能的影响并对器件的优化进行了讨论；以Tb(acac)_3bath为发光中心，发现电致发光中~5D_4→~7F_5跃迁相对~5D_4→~7F_5跃迁的增强现象；以Tfacac为第一配体，首次讨论了F取代H对于配体的三重态能级的降低和对配合物以及电致发光器件发光强度的增强作用，对于提高稀土配合物电致发光的性能提供了参考依据。对于铺配合物，以Tfacac为第一配体，以phen和bipy为第二配体，制备了红色电致发光器件并进一步验证了F取代H对于配体的三重态能级的降低作用；以HTH为第一配体，国际上首次报道了室温下Eu~(3+)离子的~5D_1→~7F_J的跃迁，并且其强度依赖于驱动电压的强度，光致发光和电致发光的不同表明二者的发光机理有所不同，并对铺配合物电致发光机理进行了讨论；以HTH为第一配体，国际上首次报道了衫配合物的电致发光现象，并且最大得到了21 cd/m~2的发光强度；为了改善稀土β-二酮配合物光稳定性和热稳定性差的缺点，引入了稀土芳香梭酸配合物，并对配体进行了引入长链的化学修饰，提高了配合物在一般有机溶剂中的溶解度，用旋涂法制备的器件的最大发光亮度达到了174 cd/m~2.

Solution-processable highly efficient yellow- and red-emitting phosphorescent organic light emitting devices from a small molecule bipolar host and iridium complexes

A bipolar transport compound, 2,5-bis(4-(9-(2-ethylhexyl)-9H-carbazol-3-yl) phenyl)-1,3,4-oxadiazole (CzOXD), incorporating both electron-and hole-transport functionalities, was synthesized and fully characterized by H-1 NMR, C-13 NMR, elemental analysis and mass spectrometry. Its thermal, electrochemical, electronic absorption and photoluminescent properties were studied

Red-Light-Emitting Iridium Complexes with Hole-Transporting 9-Arylcarbazole Moieties for Electrophosphorescence Efficiency/ Color Purity Trade-off Optimization

The synthesis, structures, photophysics, electrochemistry and electrophosphorescent properties of new red phosphorescent cyclometalated iridium(III) isoquinoline complexes, bearing 9-arylcarbazolyl chromophores, are reported. The functional properties of these red phosphors correlate well with the results of density functional theory calculations. The highest occupied molecular orbital levels of these complexes are raised by the integration of a carbazole unit to the iridium isoquinoline core so that the hole-transporting ability is improved in the resulting complexes relative to those with I-phenylisoquinoline ligands. All of the complexes are highly thermally stable and emit an intense red light at room temperature with relatively short lifetimes that are beneficial for highly efficient organic light-emitting diodes (OLEDs).

Undercut structure fabricated by complementary-structure micropatterning technique for the passive-matrix display of organic light-emitting diodes

This paper reports a new patterning method, the complementary-structure micropatterning (CSMP) technique, to fabricate the undercut structures for the passive-matrix display of organic light-emitting diodes (OLEDs). First, the polyvinylpyrrolidone (PVP) stripe patterns with a trapeziform cross-section were formed by micromolding in capillaries. Then the photoresist was spin coated on the substrate with the patterned PVP stripes and developed in water.

The role of molybdenum oxide as anode interfacial modification in the improvement of efficiency and stability in organic light-emitting diodes

It has been experimentally found that molybdenum oxide (MoO3) as the interfacial modification layer on indium-tin-oxide (ITO) in organic light-emitting diodes (OLEDs) significantly improves the efficiency and lifetime. In this paper, the role of MoO3 and MoO3 doped N,N '-di(naphthalene-1-yl)-N,N '-diphenyl-benzidine (NPB) as the interface modification layer on ITO in improvement of the efficiency and stability of OLEDs is investigated in detail by atomic force microscopy (AFM), polarized optical microscopy, transmission spectra, ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS).