Collaborative Research: Tailoring organic/semiconductor interfaces by using tunable linker dipoles

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The Chemical Structure, Dynamics and Mechanisms Program supports collaborative research between Professor Robert Bartynski of Rutgers University at New Brunswick and Professor Elena Galoppini at Rutgers University at Newark on the synthesis and characterization of tunable linker dipoles for improved solar energy conversion devices. This research, which brings together a synthetic chemist and a surface physicist, aims to achieve precise control of the electronic properties of the interface between an organic molecule and a semiconductor by tailoring the properties of the organic overlayer at the molecular level. Ultimately, this work will enhance the fundamental understanding and performance of organic-inorganic and organic-organic hybrid materials that are used in a wide variety of application areas including molecular electronics and photovoltaics. By molecular design of a variety of functional organic compounds, the research team will modify molecular energy levels (HOMO-LUMO) alignment, tune the donation and withdrawal of charge, and influence molecule bonding geometries at organic molecule/semiconductor interfaces. This will be accomplished using compounds with a Head-Linker-Anchor (HLA) configuration bound to metal oxide (TiO2 and ZnO) or organic (rubrene) semiconductor surfaces. The head groups (H) will be either organic chromophores or electron donor or acceptor groups, and the linker units (L) will contain an internal molecular dipole. The rigid linkers will be designed to bind at a well-defined orientation and distance from the semiconducting organic or inorganic surfaces. The electronic structure, dye-oxide energy level alignment, binding geometry, and effects of intermolecular interactions of HLA compounds on semiconductor substrates will be studied using a wide array, state-of-the-art ultrahigh vacuum-based surface characterization techniques. Spectroscopic and electrochemical measurements will complement the surface studies. The broader impact of this research, derived mainly from molecular level control of the organic/semiconductor interface, will touch many areas of science and technology including photocatalytic materials, photovoltaics, light-emitting diodes, and other devices. The educational component of the program will generate two innovative research modules where students gain hands-on experience that will solidify the connection between basic scientific research and technological advances that benefit society. Students will build simple solar cells based on molecules similar to those used in this research, but found in everyday items. The modules are easily adaptable for undergraduate laboratories at the two Rutgers campuses, and for demonstrations that will involve K-12 students. These activities will target underrepresented groups including high-school students from the Newark urban area. Student exchanges and co-advising of Ph.D. theses are integral to the program and the interdisciplinary collaboration between a synthetic chemist and a physicist will broaden the scientific education and training of the students from both laboratories.