Intellectual Merit. New organic components, efficient and cost-effective ways of assembling these components at the nanometer length scale, and an improved understanding of charge transport are needed for the development of efficient organic solar cells that will be cost competitive with fossil fuel technology for power generation. To achieve these properties, the photovoltaic effect in organic materials relies on three fundamental processes: 1) absorption of a photon to create a bound electron-hole pair (exciton), 2) dissociation of the exciton, and 3) transport of the electron and hole to the cathode and anode, respectively, to yield the photocurrent/voltage. There still exists a significant challenge to design new molecular components and new processing methods tailored for these components as well as to develop a deeper understanding of the charge transport process so that organic solar cells that are inexpensive and efficient can be fabricated. The objective for this proposal is to employ new fullerene and related endohedral metallofullerene derivatives to fabricate bulk heterojunctions devices with unprecedented control of the composition gradient and to study electron and hole transport in these devices in order to maximize photoconversion efficiency. Two specific aims are proposed - 1) Measure and model charge transport in photovoltaic films with tailored composition gradients; and 2) Fabricate, characterize, and optimize efficient organic solar cell devices. New combinations of electron donors and acceptors that are matched with tailored composition gradients in films are expected to lead to high performance, organic photovoltaic devices with improved photoconversion efficiencies.
Broader Impact. The development of low cost and efficient organic solar cells will lead to a number of applications that will have a significant benefit to society. This research will also advance discovery while promoting teaching and learning at the high school, undergraduate and graduate levels. This includes: 1) development of nanoscience demonstrations for Virginia Tech's Society of Physics Students outreach programs to rural, southwestern Virginia high schools, 2) coordinated recruiting of graduate students from under-represented groups with Virginia Tech's Office of Graduate Student Recruiting into a highly interdisciplinary research program, and 3) incorporation of results from this research into a course on nanotechnology taught by one of the PIs. The results of this research will be widely disseminated to the scientific and lay communities in peer-reviewed journals and in presentations at multidisciplinary conferences, in undergraduate symposia, to rural VA high school students, and in course web pages.
