Trends in den Polymerwissenschaften

This article aims to demonstrate that the fantasy of a polymer chemist needs have no limits. To achieve the targets, knowledge from all areas of chemistry, process technology, biology as well as other natural sciences comes into play. The examples given in terms of problems and solutions concentrate on challenges posed to synthetic, physical and technical chemists. Incorporating a –N=N‐function in the polymer forming the walls of micro‐capsules induces thermolability and makes the capsules suitable for use in thermal transfer printing. The inclusion of related functionalities such as–N=N–NR– or –N=N–P(O)(OR)₂– in the polymer backbone makes these especially photo‐sensitive; they can be degraded by lasers and thus specific structures can be produced. It was originally suggested that polymers were not “pure” enough for use as OLED but thanks to progress in synthetic techniques and many obvious advantages when compared with small molecules polymers are becoming increasingly important in this application. Some examples have been specifically chosen to emphasise that cooperation between synthetic and physical chemists can be particularly fruitful. The section describing the use of the Spinning Disk Reactor is an example of the influence of process technology and also an advertisement for this relatively new reactor form which, in the opinion of the author, remains underappreciated.     

White‐Light Electroluminescence with Tetraphenylethylene as Emitting Layer of Aggregation‐Induced Emissions Enhancement

Tetraphenylethylene (TPE) based molecules with easy synthesis, good thermal stability, and especially their aggregation‐induced emissions enhancement (AIEE) effect recently become attractive organic emitting materials due to their potentially practical application in OLEDs. Herein, the AIEE behaviors of tetraphenylethylene dyes (TMTPE and TBTPE) were investigated. Fabricated luminesent device using TMTPE dye as emitting layer displays two strong emitting bands: the blue emission coming from the first‐step aggregation and the yellow emission attributed to the second‐step aggregation. Thus, it can be utilized to fabricate the white‐light OLEDs (WOLEDs) of the single‐emitting‐component. A three‐layer device with the brightness of 1200 cd·m^?2 and current ef?ciency of 0.78 cd·A^?1 emits the close to white light with the CIE coordinates of x=0.333 andy=0.358, when applied voltage from 8–13 V, verifying that the TPE‐based dyes of AIEE effect can be effectively applied in single‐emitting‐component WOLEDs fabrication.     

Oligofluorene-based push-pull type functional materials for blue light-emitting diodes

A series of new oligofluorene-based push-pull type blue light-emitting functional materials, namely, 2-(9H-carbazole-9-yl)-7-(4-cyanophenyl)-9,9-dihexylfluorene (F1), 7-(9H-carbazol-9-yl)-7′-(4-cyanophenyl)-2,2′-bi(9,9-dihexylfluorene) (F2), 7-(9H-carbazole-9-yl)-7″-(4-cyanophenyl)-2,2′:7′,2″-ter(9,9-dihexylfluorene) (F3), and 7-(9H-carbazole-9-yl)-7″′-(4-cyanophenyl)-2,2′:7′,2″:7″,2″′-quarter(9,9-dihexylfluorene) (F4) were synthesized and characterized. Their onset decomposition temperatures for the thermal bond cleavage and the glass-transition temperatures were in general increased with increasing number of fluorene units. In dilute toluene solution, the oligofluorenes exhibited main absorption peaks in the range of 343-370 nm, photoluminescence maxima from 403 to 410 nm, and absolute quantum yields (Φ_PLs) of higher than 87%. In contrast, the absorption spectra of these compounds in the thin films had no large differences from those in the solutions except for the slight peak red-shifts (2-8 nm). The main emission maxima of F1, F2, and F3 in the thin films were located at 418-420 nm, while the main emission of F4 was found to be shifted to 446 nm, followed by a shoulder peak at 421 nm. The Φ_PLs of these thin films were estimated in the range of 59.2-68.7%. The existence of the electron-pull and -push end groups could effectively tune the energy levels of the oligofluorenes. By using the organic light emitting device (OLED) configuration of ITO/PEDOT:PSS/oligofluorenes/TPBi/LiF/Al by solution-process, F4 displayed the best performance: the lowest turn-on voltage (4.1 V) and highest maximum luminance (2180 cd/m²) with maximal current efficiency of 1.17 cd/A. When F4 was fabricated into the optimized device of ITO/MoO₃/NPB/CBP:F4(1:4)/TPBi/LiF/Al by vapor deposition, highest brightness of 5135 cd/m² and current efficiency of 1.76 cd/A were achieved with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.16, 0.09).     

Light extraction efficiency enhancement in organic light emitting diodes based on optimized multilayer structures

The main focus of this study is to improve the light extraction efficiency, as well as directionality of organic light emitting diodes (OLEDs) using multi-layer structures between Indium tin Oxide (ITO) and glass layers in a typical OLED. In conventional OLEDs, only about half of the light generated in the emission zone can reach to the glass substrate due to refractive index mismatch in ITO (n = 1.8?i0.01)/glass (n = 1.51) interface. The main attempt is to reduce the share of total internal reflection (TIR) and hence, the effect of different structures such as Thue-Morse and Fibonacci have been investigated and optimized with suitable layer thickness and materials based on Transfer Matrix Method (TMM). The most effective Multi-layer structures have been added to conventional OLED and have been analyzed the extraction efficiency using Finite Difference Time Domain (FDTD) method. Results show large enhancement of extraction efficiency (about 40%) in ITO/glass interface. Using this idea and applying micro-lenses array to glass substrate at the same time, one can get even higher extraction efficiency in OLED. The interesting aspect of this project is its easy fabrication process in order to commercialize the product with highest extraction efficiency and low fabrication cost.     

共轭聚合物中掺杂可溶性石墨烯对于OLED和OPV性能的影响

本文重点研究了不同浓度可溶性石墨烯(SPFGO)对于聚[2-甲氧基-5-(2-乙基己氧基)]对苯乙炔(MEH-PPV)/SPFGO复合薄膜的光致发光(PL)、 有机电致发光(OLED)和有机光伏(OPV)性能的影响. 研究发现, 在MEH-PPV中掺杂SPFGO之后, MEH-PPV/SPFGO复合薄膜的光致发光发生了非常强烈的猝灭, 意味着MEH-PPV和SPFGO之间发生了非常强烈的载流子传输. 当SPFGO的浓度较低的时候, 能够提高OLED的性能, 当SPFGO的浓度为0.2%时, OLED的性能达到最佳, 而此时的OPV性能基本没有改变. 当掺杂较高浓度的SPFGO 之后, OPV的性能有了明显的提升, 当浓度为15%时, OPV达到了最佳的性能, 而此时的OLED发生了非常强烈的猝灭. 通过实验数据可以看出, 当SPFGO较低浓度的时候, 起到增强载流子注入的作用, 提升OLED亮度的同时降低了开路电压. 而当SPFGO达到较高浓度时, SPFGO作为电子受体, 可以起到改善MEH-PPV/SPFGO 界面激子分裂和提高OPV性能的作用. 因此, 通过调节SPFGO浓度可以起到独立调控OLED性能和OPV性能的作用. 关键词： SPFGO OLED OPV     

A theory study based on DFT/TD-DFT for a series of Ir(III) complexes with the low-efficiency roll-off and the high-inter-system crossover rate properties

This study employs density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to investigate a series of cyclometallated Ir(III) complexes for their application as OLED light-emitting materials, including (dtp)₂Ir(dpm), (mmpyp)₂Ir(dpm), (dtp)₂Ir(tpip), (mmpyp)₂Ir(tpip), (dtp)₂Ir(pic), and (mmpyp)₂Ir(pic). Their geometries, frontier molecular orbital properties, ionization potential, electron affinity, absorption and emission spectra, and spin-orbit coupling properties have been analyzed respectively. Through comparison, we have identified complexes with reduced efficiency roll-off and enhanced k_ISC.     

Li掺杂8-羟基喹啉铝的密度泛函理论研究

采用密度泛函理论研究了Li原子掺杂8-羟基喹啉铝(Alq₃)分子的几何构型、 前线分子轨道及电子转移特性. 研究结果表明, Li原子掺杂Alq₃后, Li原子与Alq₃的O, N原子键合, 形成电子转移复合物. Li原子将部分电子转移到Alq₃的吡啶环上, 在Alq₃的带隙内形成施主能级, 这种n型掺杂结构有效地提高了电子的传输效率; 但过多的Li原子的掺杂会使Alq₃分解, 从而减弱其电子传输能力. 为使Alq₃的电子传输能力达到最高, Li原子的掺杂应保持在2:1左右的比例.     

以ILTO为阳极的高效有机电致发光器件

以高功函数的掺杂钛酸镧的氧化铟薄膜(ILTO)及氧化铟锡(ITO)作为阳极,制备了Glass/anode/NPB/Alq3/LiF/Al结构的有机电致发光器件。得益于ILTO较好的掺杂性、低的表面粗糙度、高的可见光透过率以及高的有效功函数,以ILTO为阳极的有机电致发光器件的开路电压得到降低,最高亮度、电流效率、功率效率以及外量子效率均获得了成倍的提高。研究结果表明,ILTO是一种潜在的光学窗口材料,有望在各种光电器件中得到广泛的应用。     

Sputter deposition of indium tin oxide onto zinc pthalocyanine: Chemical and electronic properties of the interface studied by photoelectron spectroscopy

The interface chemistry and the energy band alignment at the interface formed during sputter deposition of transparent conducting indium tin oxide (ITO) onto the organic semiconductor zinc phtalocyanine (ZnPc), which is important for inverted, transparent, and stacked organic light emitting diodes, is studied by in situ photoelectron spectroscopy (XPS and UPS). ITO was sputtered at room temperature and a low power density with a face to face arrangement of the target and substrate. With these deposition conditions, no chemical reaction and a low barrier height for charge injection at this interface are observed. The barrier height is comparable to those observed for the reverse deposition sequence, which also confirms the absence of sputter damage.     

通过插入Au薄膜改善绿光OLED器件的发光色纯度

在一些有机电致发光器件中,Au常被用作阳极,研究者希望Au在导电的同时兼具半透明可出光的属性,这要求Au在能导电的同时厚度要尽量薄。因此制备两种金属共同组成电极成为了选择。将半透明Au/Al层插入阳极一侧,制备了结构为ITO/Al(16 nm)/Au(10 nm)/TPD(30 nm)/AlQ(30 nm)/LiF(0.5 nm)/Al的OLED器件,相对于器件ITO/TPD(30 nm)/AlQ(30 nm)/LiF(0.5 nm)/Al在长波方向出现了光谱窄化现象,通过分析和实验判断该现象是Au薄膜特有的对光的选择透过性造成,而并非微腔效应。阳极一侧加入了Au/Al的器件保持了广视角无角度依赖的优点,同时可以输出滤掉部分红光的纯度更高的发光,发光色纯度得到了改善。