PITA Fiscal Year 2007 Projects

Product and Process Design and Optimization

Characterization of Contacts to Polythiophene for Organic Semiconductor Devices
The interest in organic semiconducting materials for electronic applications has shown surprising growth in the last decade. Since the discovery of conducting properties in polyacetylene in 1977 1, many other organic materials have also been found to have conducting or semiconducting properties. The versatile attributes of these materials make them particularly well suited for applications such as electronic displays on flexible substrates and large-area photovoltaics. The latter application is particularly exciting in light of the need for economical and expansive methods for renewable energy production. The low cost of producing organic semiconductor materials, in combination with theoretical efficiencies that are approaching those of amorphous silicon photovoltaics, make wide-scale production of renewable energy a realistic goal. In addition, chemical-sensing field-effect transistors (chemFET’s) based on polythiophene, one of the most widely studied classes of (semi)conducting polymers, hold promise for end-of-life sensors for gas masks and are being investigated by a group at Carnegie Mellon. Interestingly, all of these organic-semiconductor devices are severely limited by the properties of the contacts (electrodes).

In this project we propose to focus on understanding and improving the properties of ohmic contacts for polythiophene-based organic photovoltaics (OPVs) and/or chemFET’s. In this study we propose to investigate interfaces between metal contacts and semiconducting, regioregular polythiophene. Our approach emphasizes a consideration of the chemistry, the nanomorphology of the materials, and the energy level alignment at the contact-organic interfaces to improve the ohmic contacts. A variety of metal contacts will be deposited in Prof. Porter’s ultra-high vacuum deposition system. To enhance ohmic behavior, chemical bonding at the interfaces will be enhanced via regiochemical positioning of selected side chains on the base polymer. We have considered particular chemistries for high-workfunction metals, such as Pt and Au.