Probing the nanoscale phase separation in binary photovoltaic blends of poly(3-hexylthiophene) and methanofullerene by energy transfer

Organic Semiconductor Centre, School of Physics and Astronomy, SUPA, University of St Andrews, North Haugh, St Andrews, Fife, UK KY16 9SS.
Dalton Transactions (Impact Factor: 4.1). 12/2009; DOI: 10.1039/b912198f
Source: PubMed

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.
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