Critical to the overall efficiency of organics-based electronic and optical devices are the electronic processes taking place where materials come into contact. These specific interface interactions, both at the metal/inorganic-organic and organic-organic interfaces, can often dictate the successful application of a material and device.
The interface between organic semiconductors and electrodes (made of a traditional metal or a transparent conducting metal oxide) is being studied extensively because charge transfer across the interface is crucial for the performance of organic (opto)electronic devices. The energy offset between the electrode Fermi level and the frontier molecular orbitals of the organic films plays an important role in controlling the charge injection between the electrode and the charge transport material. Our computational work aims to: determine the geometric and electronic structure of organic layers which are chemically or physically adsorbed on metal or conducting oxide surfaces; evaluate the workfunction change of the electrode surfaces upon adsorption of organic layers and the alignment of the energy levels of the organic molecules with respect to the electrode Fermi level; and explore the charge transfer mechanism between electrode surfaces and organic layers.
Of equal importance, the organic-organic interfaces play a significant role in the efficiencies of exciton separation (solar cells) and/or recombination (electroluminescence), and charge transport. One area of intense interest is focused on determining the proper computational approaches, with an emphasis on density functional methods, which best describe the intermolecular interactions that control interfacial electronic properties for a broad range of compounds. In addition, we are also interested in describing the morphology of the organic-organic interface, as it plays a key role in the strength of the intermolecular interactions. Particular attention is being paid to the morphology of polymer:fullerene blends used in organic photovoltaic devices.