24 research outputs found
Long-term creatine intake is beneficial to muscle performance during resistance training
Influence of fullerene photodimerization on the PCBM crystallization in polymer: Fullerene bulk heterojunctions under thermal stress
For an increased lifetime of polymer:fullerene bulk heterojunction (BHJ) solar cells, an understanding of the chemical and morphological degradation phenomena taking place under operational conditions is crucial. Phase separation between polymer and fullerene induced by thermal stress has been pointed out as a major issue to overcome. While often the effect of thermal stress on the morphology of polymer:fullerene BHJ is investigated in the darkness, here we observe that light exposure slows down fullerene crystallization and phase separation induced at elevated temperatures. The observed photo-stabilizing effect on active layer morphology is quite independent on the polymer and is attributed to light-induced dimerization of the fullerene. (c) 2013 Wiley Periodicals, Inc
Effect of molecular weight on morphology and photovoltaic properties in P3HT:PCBM solar cells
The molecular weight of poly(3-hexylthiophene) is an important factor influencing the photovoltaic properties of bulk heterojunction organic solar cells based on this material. However, since different synthetic processes or repetitive soxhlet extractions - generally applied to obtain the different molecular weight batches under study - result in samples with simultaneously varying regioregularity (RR) and polydispersity index (PDI), it has not been possible yet to find an unambiguous correlation between the molecular weight and the photovoltaic performance. In the present work preparative gel permeation chromatography is introduced as a versatile technique to fractionate the donor polymer and thereby obtain a systematic variation of the number average molecular weight (M-n = 11-91 kg mol (1)) with an almost constant PDI and RR. Polymer crystallinity and conjugation length are evaluated by UV-Vis spectroscopy, rapid heat-cool calorimetry and selected area electron diffraction, and are found to be deeply affected by Mn. This in turn influences the behavior of the charge transfer state energy, measured via Fourier transform photocurrent spectroscopy, and therefore the open-circuit voltage. The short-circuit current is also affected by Mn, but mainly due to a change in absorption coefficient. The apparent recombination order is shown to be linked to the morphology of the polymer: fullerene blend and is determined using transient photovoltage and photocurrent techniques. Finally, a correlation between recombination and fill factor is also suggested. (C) 2015 Elsevier B.V. All rights reserved
Tectonic, magmatic and hydrothermal activity around the triple junctions of the North Fiji Basin (16° 50' S 173° 30' E and 16° 30' S 176° 10' E) (SW Pacific): Hyfiflux cruise
An audit of adverse events in children sedated with chloral hydrate or propofol during imaging studies
Simultaneous Enhancement of Solar Cell Efficiency and Stability by Reducing the Side Chain Density on Fluorinated PCPDTQx Copolymers
The
performance of polymer solar cells is strongly dependent on
the morphology of the photoactive layer, which can be optimized by
tuning the polymer side chain pattern. Whereas most studies focus
on length and bulkiness, the side chain density receives much less
attention. In this work, the effect of the number of side chains on
PCPDTQxÂ(2F) low bandgap copolymers on material properties and solar
cell characteristics is investigated. The active layer morphology
is strongly affected, affording more favorable finely intermixed blends
when decreasing the side chain density. As a result, the efficiency
increases to a maximum of 5.63% for the device based on the copolymer
with intermediate side chain density. Moreover, removal of the side
chains also has a positive effect on device stability under prolonged
thermal stress. A single structural parameterî—¸alkyl side chain
densityî—¸is hence used for simultaneous enhancement of both
solar cell efficiency and lifetime