Organic semiconductors: Healing contact

Lee and co-workers demonstrate that the simple application of a polymer oil based on a perfluoropolyether (PFPE) to the surface of an organic semiconducting crystal markedly reduces the influence of traps and results in the ability to measure the charge-carrier transport properties of π-conjugated materials with high accuracy. These researchers investigated the hole mobility in single crystals of rubrene and tetracene, two of the highest-performing hole transporters in OFETs. They deposited on the surface of the crystals a thin layer of a non-conjugated polymer, PFPE. To explain the nature of the PFPE-crystal interaction, Lee and colleagues postulate that dipole moments associated with the pendant trifluoromethyl groups protruding from the PFPE backbone align and induce a local electric field at the interface, thereby creating a hole-accumulation layer. The increased sensitivity of the Hall effect measurements allows the researchers to confirm that hole transport in rubrene is indeed in the band regime, whereas holes in tetracene seem to move by means of an incoherent hopping mechanism.