Indium-Tin-Oxide (ITO) Work Function Tailoring by Covalently Bound Carboxylic Acid Self-Assembled Monolayers

Tuning the work function of electrodes is crucial to improve the carrier injection into organic optoelectronic devices in order to minimize energy losses. We have analyzed and explored the potential of self-assembled monolayers (SAMs) covalently bound to an electrode to tune its work function for optimized organic optoelectronic devices. A systematic experimental photoelectron spectroscopy study of several carboxylic acid SAMs, deposited onto indium-tin-oxide (ITO), reveals work function changes up to 1.8eV. Subsequently, the effects of different SAMs on the injection barrier in organic thin film transistors and thus their efficiency are studied. The data obtained can be described qualitatively, regarding the key factors for work function tuning, i.e., the intrinsic molecular dipole, the energetic position of the conducting molecular orbital as calculated by DFT and the contribution of the chemical bond at the electrode-SAM interface. Using the insights gained from the applied theoretical descriptions of work function tuning combined with the experimental findings, work function tailoring can be made possible and enables the design of an energetic matching interface.