A New Route to Low Resistance Contacts for Performance-Enhanced Organic Electronic Devices

The barrier to charge carrier injection across the semiconductor/electrode interface is a key parameter in the performance of organic transistors and optoelectronic devices, and the work function of the electrode material plays an important role in determining the size of this barrier. We present a new, chemical route for making metal surfaces with low work functions, by functionalizing gold surfaces with self-assembled monolayers of n,n-dialkyl dithiocarbamates. Ultraviolet photoemission spectroscopy measurements show that work functions of 3.2 eV +/- 0.1 eV can be achieved using this surface modification. Electronic structure calculations reveal that this low work function is a result of the packing-density, polarization along the N-C bond, and charge rearrangement associated with chemisorption. We demonstrate that electrodes functionalized with these monolayers significantly improve the performance of organic thin-film transistors and can potentially be employed in charge selective contacts for organic photovoltaics.