Hole-injection from a polar mono-molecular layer derivatised ultra-thin gold electrode into a triphenylamine derivative

This Letter, reports the hole-injection characteristics of an ultra-thin, transparent gold electrode derivatized with a thiolate polar monolayer into the amorphous molecular semiconductor, N,N′-bis(3-methylphenyl)-N,N′diphenyl-1,1′biphenyl- 4,4′-diamine (TPD). Thermionic emission with image force lowering gives an excellent description of the injection mechanism over a large range of temperatures and electric field strengths, yielding a zero field Schottky barrier height of ∼0.4 eV. This study demonstrates that derivatizing the surface of this novel gold electrode with a 4-nitrophenylthiolate monomolecular layer is an effective means of circumventing the abrupt negative vacuum level shift, which forms when TPD is thermally deposited onto gold electrodes.