Polythiophene Derivatives -Based Materials for Organic Field Effect Transistors and Photovoltaic Cells

Polythiophenes, their copolymers with fluorenones and their terpolymers containing thienylene, fluorenone and vinylene units are very promising candidates for the fabrication of organic electronic devices such as field effect transistors (FETs) or photovoltaic cells (PC). Their application requires not only the development of new synthetic techniques which yield macromolecules of a regular chain microstructure but also strict control of macromolecular parameters such as molecular weight and its distribution. Among polythiophenes, three seem especially promising as active components of organic FETs, these are: regioregular poly(3-hexylthiophene) (PHT), poly(3,3"-dioctyl-2,2\´:5\´,2"-terthiophene) (PDOTT) and poly(2,5bis(3-alkylthiophen-2-yl) thieno[3,2-b] thiophene)s (PTTT). Both PHT and PDOTT exhibit an interesting phenomenon of strong dependence of their carriers\´ mobility on molecular weight, Mn, which persists to rather high Mn values, changing form 10⁵ cm²/V.s to give the values to 10^-2 cm²/V.s for polymers exhibiting Mn of 0.84 kDa and 120 kDa respectively. Poly[(5,5\´-(bis-(E)-l,2-bis(3-octylthien-2-yl)ethylene]-alt-(2,7-fluoren- 9-one) ](PTVF) is, in turn, an interesting candidate for photovoltaic applications. This carefully designed, solution processible polymer, containing complementary chromophores to better match the solar spectrum, can be used for the fabrication of PC in the bulk heterojunction configuration with PCBM (C₆₀ derivative). Presently fabricated PTFV based PC show efficiencies 1%, however the presented synthetic approach, together with the optimization of the processing conditions, should lead, in the near future, to a significant improvement of this parameter