Polymer solar cells have evolved as a promising costeffective alternative to inorganic-based solar cells [1,2] due to their potential to be low-cost, light-weight, and flexible. Since the discovery of ultrafast photoinduced charge transfer from a conjugated polymer to fullerene molecules, followed by the introduction of the bulk heterojunction (BHJ) concept, [3] intensive research with potential materials has been carried out as future photovoltaic (PV) technology. [4][5][6][7][8] Two organic materials with distinct donor and acceptor properties are required to form a heterojunction in the bulk film, which is often achieved by solution processing. In such a case, the BHJ not only provides abundant donor/acceptor interfaces for charge separation, but also forms an interpenetrating network for charge transport. [8,9] Highly efficient polymer solar cells based on poly(3-hexylthiosphene) (P3HT) and [6,6]-phenyl C 61 butyric acid methyl ester (PC 61 BM) have been reported with power conversion efficiencies of 4-5%. [6,[10][11][12] The two most decisive parameters regarding polymer-solar-cell efficiencies are the open-circuit voltage (V oc ) and the short-circuit current (J sc ). J sc is mostly determined by the light absorption ability of the material, the charge-separation efficiency, and the high and balanced carrier mobilities. On the other hand, V oc is limited by the difference in the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor, where a small V oc (as compared to the photon energy) represents a smaller driving force for the PV process. For the P3HT:PC 61 BM system, the V oc is around 0.6 V, which significantly limits the overall device efficiency. An effective method to improve the V oc of polymer solar cells is to manipulate the HOMO level of the donor and/or LUMO level of the acceptor.[13] Until now, fullerene derivatives have proved to be one of the best and most commonly used electron acceptors. Fortunately, it is convenient to change the band gap and energy levels of the donor material by modifying the chemical structure to achieve a high V oc . [13,14] Amongst various polymers, poly{[2,7-(9-(20-ethylhexyl)-9-hexylfluorene])-alt- [5,50-(40, 70-di-2-thienyl-20,10,30-benzothiadiazole)]} (PFDTBT) has a deep HOMO level, which leads to a large V oc when blended with PC 61 BM. Svensson et al. [15] have reported polymer PV cells with a V oc of 1 V based on alternating copolymer PFDTBT blended with PC 61 BM. Moreover, Inganäs et al.[16] reported a systematic study of PV cells using four different fluorene copolymers by varying the length of the alkyl side chain and chemical structure, exhibiting power conversion efficiencies above 2-3%. Unfortunately, in their case, the low photocurrent becomes a major limiting factor in achieving higher efficiencies, suggesting low carrier mobilities.In this study, poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-2 0 -thienyl-2,1,3-benzothiadiazole)]} (BisEH-PFDTBT) and poly{[2,7-(9,9-bis-(3,...
Photoelectron spectroscopy was used to investigate poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61 butyric acid methyl ester (PCBM), and their blends on various conductive substrates. The study shows a P3HT-rich layer at the top of the P3HT:PCBM blend films. The energy level alignment of the top P3HT changes with the work function of the substrate and the PCBM concentration at the bottom surface of the blend film. The results can be explained using the integer charge transfer model.
In this letter, we investigate electronic structures and electron-injection mechanisms of the effective cathode structures for organic light-emitting devices incorporating cesium carbonate ͑Cs 2 CO 3 ͒, either deposited as an individual thin injection layer or doped into the organic electron-transport layers. The electronic structures and the interface chemistry studied by ultraviolet and x-ray photoemission spectroscopy show that the enhanced electron injection is associated with strong n-doping effects and increase of electron concentrations in the electron-transport layer induced by Cs 2 CO 3. Since such a reaction occurs without the presence of metals, cathode structures incorporating Cs 2 CO 3 may be applied to a wide range of electrode materials.
Abl tyrosine kinase (Abl) regulates axon guidance by modulating actin dynamics. Abelson interacting protein (Abi), originally identified as a kinase substrate of Abl, also plays a key role in actin dynamics, yet its role with respect to Abl in the developing nervous system remains unclear. Here we show that mutations in abi disrupt axonal patterning in the developing Drosophila central nervous system (CNS). However, reducing abi gene dosage by half substantially rescues Abl mutant phenotypes in pupal lethality, axonal guidance defects and locomotion deficits. Moreover, we show that mutations in Abl increase synaptic growth and spontaneous synaptic transmission frequency at the neuromuscular junction. Double heterozygosity for abi and enabled(ena) also suppresses the synaptic overgrowth phenotypes of Abl mutants, suggesting that Abi acts cooperatively with Ena to antagonize Abl function in synaptogenesis. Intriguingly, overexpressing Abi or Ena alone in cultured cells dramatically redistributed peripheral F-actin to the cytoplasm, with aggregates colocalizing with Abi and/or Ena, and resulted in a reduction in neurite extension. However, co-expressing Abl with Abi or Ena redistributed cytoplasmic F-actin back to the cell periphery and restored bipolar cell morphology. These data suggest that abi and Ablhave an antagonistic interaction in Drosophila axonogenesis and synaptogenesis, which possibly occurs through the modulation of F-actin reorganization.
Work-related fatigue should be monitored, particularly for new nurses who work more than 10 hr per day and who have greater workloads.
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