Electrode-molecular semiconductor contacts: Work-function-dependent hole injection barriers versus Fermi-level pinning

Contacts between two molecular organic semiconductors [p-sexiphenyl (6P) and pentacene] and conducting polymers (CPs) were investigated with photoemission spectroscopy. The dependence of the hole injection barrier (HIB) at 6P/CP interfaces on substrate work function (phi) exhibited a transition from almost Schottky-Mott limit-like behavior to Fermi-level pinning. For pentacene, no significant variation of the HIB as function of phi was observed, despite the large range of phi spanned by the CPs (4.4 - 5.9 eV). The results on contacts with CPs are compared to those with metals, where none of the two limiting cases for HIBs as a function of phi was observed. (c) 2006 American Institute of Physics.