Titanium dioxide surface energy levels tuning by self-assembled monolayers

Abstract

Tailoring the work function of functional layers in an optoelectronic device is an important means for performance improvement, as it results in changes in charge extraction or recombination. One way to proceed is to adsorb molecules with varying dipole moment strengths and signs. In this communication, the surface of anatase TiO2 is modified using different self-assembled monolayers (4-chlorobenzoic acid, 4-nitrobenzoic acid, 4-methoxybenzoic acid, and β-alanine) and the energetics at the interface is determined using a series of photoelectron spectroscopy techniques, namely, ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and inverse photoemission spectroscopy. The observed changes in work function are correlated with the dipole moments of the respective acids, calculated by density functional theory. Finally, the relevance of this interfacial engineering for controlling the charge extraction from an optoelectronic device is illustrated.