Princeton University

School of Engineering & Applied Science

Engineering Interfacial Properties of Organic Semiconductors Through Soft-Contact Lamination and Surface Functionalization

Andrew Shu
Engineering Quadrangle J401
Monday, May 19, 2014 - 2:00pm to 3:30pm

     Organic electronics is a topic of interest due to its potential for low temperature and solution processing for large area and flexible applications. Examples of organic electronic devices are already available on the market; however these are, in general, still rather expensive. In order to fully realize inexpensive and efficient organic electronics, the properties of organic films need to be understood and strategies developed to take advantage of these properties to improve device performance. This work focuses on two strategies that can be used to control charge transport at interfaces with active organic semiconducting thin films.
     Vacuum evaporated molecular organic devices have long used layer stacking of different materials as a method of dividing roles in a device and modifying energy level alignment to improve device performance and efficiency. Applying this type of architecture for solution-processed devices, on the other hand, is nontrivial, as an issue of removal of or mixing with underlying layers arises. We present and examine here soft-contact lamination, in which dry films are essentially pressed together using a rubber-like stamp, as a viable technique for depositing solution-processed multilayer structures.
Double-layer films of a single polymer material are formed to compare their energy levels and charge transport characteristics with single-layer films. The interface formed by soft-contact lamination is found to be transparent with respect to electronic charge carriers.
     We also propose a technique for modifying electronic level alignment at interfaces between two different organic films using molecules that chemically attach to a surface and shift energies. An ultra-thin metal oxide is first deposited on top of the bottom organic film as an adhesion layer for these molecules. The deposition of the metal oxide is shown to be successful for a variety of organic films. A series of molecules is then attached to the surface of the thin metal oxide on the organic film and found to modify the energy level alignment, with varying strengths, between two organic films after a second organic film has been deposited on top.