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25 September 2008Development of Si-bridged conjugated donor polymers for high-efficiency bulk-heterojunction photovoltaic devices
We report the synthesis and photovoltaic properties of poly[2,7-(9,
9-di-n-octyl-silafluorene)-alt-5,5''-(4',
7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PSiF-DBT). The polymer heterojunction solar cells fabricated from PSiF-DBT as the electron
donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor exhibited a high powerconversion
efficiency up to 5.4% with an open-circuit voltage of 0.90 V, a short-circuit current density of 9.5 mA cm-2
and a fill factor of 50.7% under the illumination of AM 1.5 G from a solar simulator (800 W m-2). A comparative study
between PSiF-DBT and its polyfluorene analogous PFDTBT and PFO-DBT demonstrates that the high performance of
PSiF-DBT originated from its red-shifted absorption spectrum up to 680 nm and high mobility of 1 × 10-3 cm2 V-1 s-1 compared with 645 nm and 3 × 10-4 cm2
V-1 s-1 for corresponding polyfluorene derivatives, respectively. These results indicate polysilafluorene derivatives are a promising new class of donor materials for polymer solar cells.