  We demonstrate an approach to improve poly-3-hexylthiophene field effect
transistors by modifying the gold contacts with monolayer thick
pentacenequinone (PQ) or naphthalene (NL). The effective contact resistance is
reduced by a factor of two and sixteen for interlayers of PQ and NL,
respectively. The observation is attributed to different injection barriers at
the metal-organic interface caused by the functionalization and to an
additional tunneling barrier enhancing the on/off ratios. This barrier yields
to activation energies of 37meV (NL) and 104meV (PQ) below 190K, which are
smaller than without functionalization, 117meV.
