Field-effect transistors based on poly(3-hexylthiophene): Effect of impurities

Organic field-effect transistors (OFETs) based on regioregular poly(3-hexylthiophene)s (P3HT)s have been studied as a function of the amount of impurities in the active polymer. P3HTs have been synthesized via a nickel-initiated cross-coupling polymerization and successively purified by a series of Soxhlet extractions with methanol, hexane and chloroform. At each stage, the amount of impurities was quantified by means of 1H nuclear magnetic resonance (NMR) spectroscopy, Rutherford backscattering spectroscopy (RBS) and particle induced X-ray emissions (PIXE). Traces of Ni, Cl, Mg, Ca, Fe and Zn could be detected in non-fully purified P3HTs. The presence of impurities in the different fractions of P3HT is shown to affect not only the characteristics of the OFETs but also the photovoltaic performances.