Development of novel processable electron accepting conjugated polymers containing fluoranthene units in the main chain

Considerable interest exists in the development of novel n-type conjugated polymers, since many currently available polymer systems have insufficient electron mobility and/or electron affinity. In this work, a universal synthesis route is presented towards a new class of n-type conjugated polymers, i.e. poly(p-fluoranthene vinylene) (PFV) and its derivatives. This route is illustrated with three examples, i.e. unsubstituted PFV and functionalized hexyl-PFV and dodecyl-PFV. All polymers have been synthesized via the dithiocarbamate precursor route. Solubility was introduced by incorporation of alkyl side chains, which leads to a significantly enhanced purity and processability as compared to unsubstituted PFV. Under the applied electrochemical conditions PFV-type polymers demonstrate typical n-type behavior. Additional CELIV mobility measurements on dodecyl-PFV reveal an excellent electron mobility, μ_e = 1.4 × 10⁻⁴ cm²/Vs. Hence, poly(p-fluoranthene vinylene) and its derivatives are promising n-type materials for organic optoelectronic applications.     

A three-chamber electrochemical cell facilitated biogas upgrading and high-purity oxygen production

Journal of Applied Electrochemistry - Anion exchange membrane (AEM)-equipped electrochemical cells can be used for removing the carbon dioxide (CO2) from biogas, thereby upgrading its energy...     

Influence of processing additives to nano-morphology and efficiency of bulk-heterojunction solar cells: A comparative review

Research and development towards high efficiency plastic solar cells have been accelerating in recent years. Polymer-based bulk heterojunction solar cells are offering an attractive and inexpensive concept for large scale production by solution processing as well as advantageous flexible and aesthetic form factors. The thin film nano-morphology of bulk-heterojunction solar cells has been shown to dramatically influence the photovoltaic performance of the devices. This article reviews the different methods used to control the film nano-morphology of bulk-heterojunction solar cells focussing on the chemical additives during solution processing. All power conversion efficiency limiting mechanisms of bulk-heterojunction solar cells are discussed in detail. It is shown, how the formation of optimal percolation pathways between donor and acceptor influences the photovoltaic device performance. It is explained how the film nano-morphology relates to light absorption, free charge carrier generation as well as charge transport to the electrodes.     

告别纪念碑的广场——维尔纽斯公共空间的晦暗命运

波罗的海之滨的新国家立陶宛是1990年从前苏联独立出来的。像其他前苏联的城市一样,在首都维尔纽斯的公共空间中,代表苏联意识形态的大部分纪念碑都被轰然捣毁或者被逐渐拆除。而全国其他地方的一部分这类纪念碑不久被送到所谓的格鲁塔斯公园(或者叫"斯大林的世界"——这一称谓是作者与英国的城市规划专家马尔科姆F.迈里斯谈话时提及的)。在这里,相当多的,作为苏联统治遗产的奇特收藏物被私人收藏,这一地点也变成东欧的知名场所。立陶宛首都的很多公共空间和全国的其他城市也经历了重大的修缮。这些修缮的首要目的是摧毁以前的极权象征以及共产主义意识形态。但是,不平稳的经济发展、缺乏市政基金以及城市规划明确方向,导致重新设计公共空间的工程被放弃。直到今天,维尔纽斯那些以前的纪念碑已经被拆除的广场和其他类型公共空间,依然是废弃的状态。没有或者几乎没有任何做为了当今社会的需要而重新塑造其结构和外观的事情。在某些情况下,被清空的公共空间留下了一类未完工的和最近毁坏的建筑场地,成为了年轻人或黑帮分子进行涂鸦表演的场所,居民们惟恐避之不及(尤其是黄昏后)。在这里,以前混凝土设置的部件看起来就像战争或者任何其它类型社会灾难产生的遗物。尽管明显需要修缮,市政当局以及建筑师、城市规划者、艺术家和遗产保护部门等公共机构却仍然继续就它们的将来无休止地进行争论。对应该建设什么来代替被摧毁的苏联的象征,或是对其进行保留,或是重新设计为供城市居民休闲或活动等更为亲民的空间,至今还看不到作出决定的希望。     

Fluorene‐Carbazole Dendrimers: Synthesis,Thermal, Photophysical and Electroluminescent Device Properties

Novel hole‐transporting dendrimeric molecules containing dioctylfluorene, spirobi(fluorene) and spiro(cylododecane‐fluorene) as the core unit and different numbers of carbazole and thiophene moieties as the peripheral groups are synthesized. All the dendrimers are characterized by ¹H NMR, ¹³C NMR, FTIR, UV–vis, PL spectroscopy, and MALDI‐TOF. They are thermally stable with high glass transition and decomposition temperatures and exhibit chemically reversible redox processes. They are used as the hole‐transporting layer (HTL) material for multilayer organic light emitting diodes (OLEDs) with a low turn‐on voltage of around 2.5 V and a bright green emission with a maximum luminance of around 25400 cd m^?2.     

Molecular glasses possessing a phenyl-1,2,3,4-tetrahydroquinoline moiety as hole transporting materials for electrophotography

The new hole transporting materials which comprise molecules consisting of two hydrazone branches linked with flexible thiobiphenyl or thiophenyl sulphide and two hydroxyl groups containing central bridge were synthesized and investigated. These transporting materials possessing phenyl-1,2,3,4-tetrahydroquinoline moieties are low molecular glasses and allow preparing stable to crystallization layers. The ionization potentials of these compounds are ca. 5.3 eV as determined by the electron photoemission method. These low molecular glasses can be used as hole transporting materials with or, in the case of a solid substrate, without binder polymer. The hole drift mobility of the newly synthesized compounds, measured by xerographic time of flight method, exceeds 10⁻⁵ cm²/V s at an electric field of 10⁶ V/cm.     

Interactions between flavour release and rheological properties in model custard desserts: Effect of starch concentration and milk fat

The influence of the concentration of various reagents and of the storage time on the flavour release of custard desserts was evaluated by headspace solid-phase microextraction and supported by rheological measurements. The presence of milk fat induced a significant decrease of the headspace concentration of flavour compounds, mainly due to hydrophobic matrix–flavour interactions. An elevated starch concentration enhanced the strength of the custard gels considerably. However, the increasing starch concentration resulted in an increased flavour release at low flavour concentrations, while a tendency to flavour retention was noted at higher flavour concentrations. During storage time, a denser network was formed as shown by rheological measurements, but no significant difference in flavour release was noted upon storage (three days). These results show that the complex interactions between flavour compounds and the food matrix in a model custard are difficult to predict and have to be carefully evaluated by a combination of rheological parameters and physicochemical interactions.     

Use of hollow core fibers, fiber lasers, and photonic crystal fibers for spark delivery and laser ignition in gases

The fiber-optic delivery of sparks in gases is challenging as the output beam must be refocused to high intensity (approximately 200 GW/cm(2) for nanosecond pulses). Analysis suggests the use of coated hollow core fibers, fiber lasers, and photonic crystal fibers (PCFs). We study the effects of launch conditions and bending for 2 m long coated hollow fibers and find an optimum launch f# of approximately 55 allowing spark formation with approximately 98% reliability for bends up to a radius of curvature of 1.5 m in atmospheric pressure air. Spark formation using the output of a pulsed fiber laser is described, and delivery of 0.55 mJ pulses through PCFs is shown.     

Investigation of new PPV-type polymeric materials containing fluorene and thiophene units and their application in organic solar cells

New poly(p-phenylenevinylene) (PPV)-type conducting polymers containing different concentrations of thiophene and fluorene functional units were investigated in this work and the photophysical and electrochemical properties were evaluated. We observed a dependence of these properties on the concentration of thiophene units in the polymer backbone. The hole mobilities were estimated to be on the order of 10^?6 cm² V^?1 s^?1. The polymers were combined with different concentrations of a soluble fullerene derivative (PCBM) and applied in bulk-heterojunction photovoltaic cells. The effects of PCBM concentration and of annealing (post-production treatment) on these devices were investigated. The best results were obtained for the materials containing higher concentrations of thiophene units.