Probing the nanoscale phase separation in binary photovoltaic blends of poly(3-hexylthiophene) and methanofullerene by energy transfer
ABSTRACT The generation of charge carriers in organic photovoltaic devices requires exciton diffusion to an interface of electron donor and acceptor materials, where charge separation occurs. We report a time resolved study of fluorescence quenching in films of poly(3-hexylthiophene) containing a range of fractions of the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We show that energy transfer from P3HT to PCBM helps to bring excitons to the interface, where they dissociate into charge carriers. Fluorescence quenching in blends with < or = 50 wt% of PCBM is controlled by exciton diffusion in P3HT. This allows us to estimate the average size of PCBM domains to be about 9 nm in the 1:1 blend. The implications for polymer solar cells are discussed.
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ABSTRACT: Charge transfer behavior of Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl eser (PCBM) in solutions and in films were examined by photoluminescence (PL) spectroscopy. PL study in solutions indicated that separation distance between P3HT and PCBM affected charge transfer efficiency more seriously than the interface area issue between P3HT and PCBM. P3HT/PCBM film showed very effective photo-induced charge transfer before post-thermal annealing on the bi-layer P3HT/PCBM film. Charge transfer efficiency was gradually diminished by the annealing-induced phase separation between P3HT and PCBM as revealed by increasing PL emission intensity of P3HT.05/2013; 60(5). DOI:10.1002/jccs.201200485
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ABSTRACT: Exciton diffusion length strongly impacts the performance of organic photovoltaic cells and light emitting diodes, and therefore ways of manipulating the diffusion length must be sought out. Here, we present an approach for controlling singlet exciton diffusion in triphenylamine (TPA)-based amorphous films via incorporation of phenylethenyl sidearms. Exciton diffusion of the TPA derivatives possessing different number (one, two and three) and different type (2-methyl-2-phenylethenyl, 2,2-diphenylethenyl and 2,2-di(4-methoxyphenyl)ethenyl) of sidearms was investigated by employing the volume quenching method in combination with Monte Carlo simulation of 3D exciton diffusion. A nearly three-fold enhancement of the exciton diffusion length by increasing the number of peripheral phenylethenyl groups from one to three was achieved mainly due to the enhanced overlap of the emission and absorption spectra. The dominance of the spectral overlap integral in determining energy transfer rates was confirmed by calculations based on Förster energy transfer theory, which also proved a key role of phenylethenyl sidearms in facilitating exciton diffusion.05/2014; 2(24). DOI:10.1039/C4TC00262H
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ABSTRACT: We report three generations of dendrimers incorporating either a fluorene or spirobifluorene core with carbazole dendrons and fluorene surface groups that are effective sensing materials for the detection of nitrated explosives by fluorescence quenching. The photophysical properties of the dendrimers were investigated with a combination of steady-state absorption and photoluminescence and time-resolved photoluminescence. We show that the first-generation dendrimers behave as single chromophores while the higher-generation dendrimers contain multiple chromophores that interact to give excimer-like emissive states. Stern–Volmer measurements with nitrated analytes show that the quenching efficiency decreases with generation for the planar fluorene-cored dendrimers and increases with generation for the more three-dimensional spirobifluorene-cored dendrimers. These contrasting trends are shown to be caused primarily by changes in the quenching efficiency of static interactions with the nitrated analytes, which is a consequence of the choice of core. Our results highlight the potential for exploiting such excimer-like states for chemical sensing, particularly in the case of nitrated explosives.The Journal of Physical Chemistry C 03/2013; 117(10):5328–5337. DOI:10.1021/jp4002884 · 4.84 Impact Factor