175 research outputs found
The influence of polymer purification on the efficiency of poly(3-hexylthiophene):fullerene organic solar cells
Confinement Effects on the Crystalline Features of Poly(9,9-dioctylfluorene)
Typical device architectures in polymer-based optoelectronic devices, such as
field effect transistors organic light emitting diodes and photovoltaic cells
include sub-100 nm semiconducting polymer thin-film active layers, whose
microstructure is likely to be subject to finite-size effects. The aim of this
study was to investigate effect of the two-dimensional spatial confinement on
the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene)
(PFO). PFO melts were confined inside the cylindrical nanopores of anodic
aluminium oxide (AAO) templates and crystallized via two crystallization
strategies, namely, in the presence or in the absence of a surface bulk
reservoir located at the template surface. We show that highly textured
semiconducting nanowires with tuneable crystal orientation can be thus
produced. Moreover, our results indicate that employing the appropriate
crystallization conditions extended-chain crystals can be formed in
confinement. The results presented here demonstrate the simple fabrication and
crystal engineering of ordered arrays of PFO nanowires; a system with potential
applications in devices where anisotropic optical properties are required, such
as polarized electroluminescence, waveguiding, optical switching, lasing, etc
Effect of excited states and applied magnetic fields on the measured hole mobility in an organic semiconductor
Copyright 2010 by the American Physical Society. Article is available at
Concepções de professores paranaenses sobre a natureza do conhecimento cientÃfico: permanências e rupturas
Apresenta resultados de pesquisa com professores de quÃmica da rede pública de ensino do Estado do Paraná no Brasil. Estudamos as concepções desses docentes sobre a natureza do conhecimento cientÃfico e identificamos rupturas e permanências da visão geral que docentes têm sobre ciência. Aplicamos questionário a 62 professores com questões sobre a ciência e sua natureza. A maioria dos professores revela visões de ciência empÃrico-indutivista. Indicam a melhoria das atividades didáticas exclusivamente pela inserção de experimentos guiados pelo método cientÃfico. Este trabalho aponta para a necessidade de inserirmos na formação de professores a história e filosofia da ciência no intuito de melhorar a concepção docente sobre a ciência
A low band gap co-polymer of dithienogermole and 2,1,3-benzothiadiazole by Suzuki polycondensation and its application in transistor and photovoltaic cells
Excitonic coupling dominates the homogeneous photoluminescence excitation linewidth in semicrystalline polymeric semiconductors
We measure the homogeneous excitation linewidth of regioregular
poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by
means of two-dimensional coherent photoluminescence excitation spectroscopy. At
a temperature of 8\,K, we find a linewidth that is always \,meV
full-width-at-half-maximum, which is a significant fraction of the total
linewidth. It displays a spectral dependence and is minimum near the 0--0
origin peak. We interpret this spectral dependence of the homogeneous
excitation linewidth within the context of a weakly coupled aggregate model.Comment: 13 pages, 4 figures, Supplementary Materia
Electron spin relaxation in organic semiconductors probed through muSR
Muon spin spectroscopy and in particular the avoided level crossing technique
is introduced, with the aim of showing it as a very sensitive local probe for
electron spin relaxation in organic semiconductors. Avoided level crossing data
on TMS-pentacene at different temperatures are presented, and they are analysed
to extract the electron spin relaxation rate, that is shown to increase on
increasing the temperature from 0.02 MHz to 0.33 MHz at 3 K and 300 K
respectively.Comment: International Conference TSN2010 "Trends in spintronics and
nanomagnetism
New 3,3'-(ethane-1, 2-diylidene)bis(indolin-2-one) (EBI)-based small molecule semiconductors for organic solar cells
A series of new donor–acceptor–donor (D–A–D) small-molecule compounds, with 3,3′-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) as an electron acceptor building block coupled with various electron donor end-capping moieties (thiophene, bithiophene and benzofuran), were synthesized and characterized. When the fused-ring benzofuran is combined to EBI (EBI-BF), the molecules displayed a perfectly planar conformation and afforded the best charge transport properties among these EBI compounds with a hole mobility of up to 0.02 cm2 V−1 s−1. All EBI-based small molecules were used as donor material along with a PC61BM acceptor for the fabrication of solution-processed bulk-heterojunction (BHJ) solar cells. The best performing photovoltaic devices are based on the EBI derivative using the bithiophene end-capping moiety (EBI-2T) with a maximum power conversion efficiency (PCE) of 1.92%, owing to the broad absorption spectra of EBI-2T and the appropriate morphology of the BHJ. With the aim of establishing a correlation between the molecular structure and the thin film morphology, differential scanning calorimetry, atomic force microscopy and X-ray diffraction analysis were performed on neat and blend films of each material
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