AMINO ACIDS BASED-MONOLAYERS FOR TUNING ELECTRONIC PROPERTIES OF CONDUCTIVE OXIDES

Organic based optoelectronics devices have a promising potential in various applications. Energy band alignment at interfaces between the organic layers and indium tin oxide (ITO), a commonly used electrode, is extremely important for the efficiency of these devices. Using organic monolayers as a mean to control the work function of the conductive oxide via the molecular dipole moment and/or charge redistribution has shown to be an effective way for tailoring the interfacial electronic properties without hindering the overall performance of such devices. In this respect, amino acids provide a versatile platform to control ITO work function, since they easily form monolayers by attaching to the surface through their carboxylic residue, enabling their side groups to tune the electronic properties. Here, we show the effect of selected amino acids` side chain on the electronic properties of ITO.

Monolayers of Lysine, Glutamic acid and Tyrosine were assembled on ITO in order to study the effect of positively charged, negatively charged and aromatic side chains (respectively) on the work function and surface photovoltage of the surface, while bare ITO and Glutamine (uncharged side chain) were chosen as reference. Our results show that Lysine monolayers decrease the work function due to positive dipole moment while Tyrosine monolayers increase the work function due to negative dipole moment. Glutamic acid monolayers decrease the work function, probably due to adsorption through both carboxylic groups. Surface photovoltage spectroscopy studies show an increase in the band bending in all cases, except for Tyrosine, in respect to bare ITO, showing charge redistribution at the surface. These results present a simple and versatile process for tuning the electrical properties of conductive oxide surfaces using amino acids.