Electrophoretic deposition of the thiophene-based copolymer and its composites with C60.

Electrophoretic deposition is a useful and efficient technique to deposit conjugated polymers, if suitable suspension of the target polymer is obtained. Unfortunately, neither general theory nor universal procedure for the preparation of a suspension suitable for electrophoretic deposition has seemed to be established yet. Thus, accumulation of individual knowledge is still important in this area. Here, the preparation of suspensions of a thiophene-based polymer poly(3-octylthiophene-2,5-diyl-co-3-decyloxythiophene-2,5-diyl) (POT-co-DOT) and their application to the electrophoretic deposition have been reported. The suspensions of POT-co-DOT with various good/poor solvents ratios were easily obtained by mixing a toluene solution of the polymer and acetonitrile. The composition of the dispersion medium significantly affects the surface morphology of the film prepared by the electrophoretic deposition in the suspension. Composite films consisting of POT-co-DOT and C(60) have also been successfully prepared by electrophoretic deposition. Because the optical absorption peak at 333 nm in C(60) showed neither significant broadening nor a red shift, C(60) molecules were expected to be well-dispersed in the composite films. A photovoltaic device with a composite film prepared from a POT-co-DOT/C(60) = 2:1 suspension showed 10 times larger short-circuit current density and 5 times larger power conversion efficiency than a device with pure POT-co-DOT, although further work is required to improve the device performance.