π-Conjugated donor-acceptor small molecule thin-films on gold electrodes for reducing the metal work-function

This paper reports the design, facile synthesis and purification of four π-conjugated donor-acceptor small molecules comprising heteroaromatic units, DA-1-DA-4, for surface and electronic structure modification of gold thin film. These molecules were characterized by 1H/13C nuclear magnetic resonance spectroscopy, cyclic voltammetry, UV-Vis spectroscopy, and single-crystal X-ray diffraction. Morphologically smooth thin-films (~ 5 nm) of DA-1-DA-4 were deposited onto Au thin films via thermal evaporation and characterized by atomic force-microscopy, θ-2θ X-ray diffraction and ultraviolet photoelectron spectroscopy. The work functions of the small molecule coated Au electrodes are shifted to lower energies by ~ 0.1-0.3 eV, compared to that of the bare Au film measured as a reference. The vapor-deposition of structurally simple small molecules developed here shows great promise as a facile approach to reduce gold work function for electron injection/extraction between organic semiconductors and Au contacts in various opto-electronic devices.