Technical. The project aims for greater understanding of, and the ability to enhance, the exciton dissociation rate in organic solar cells, and generally, to accurately determine the fraction of dissociated charge across individual organic/organic and organic/inorganic interfaces. The long-term goal is, through more complete understanding of the exciton dissociation process, to develop a strategy for improving organic solar cell efficiency to levels closer to that achieved in inorganic materials. Spin filtering materials and heavy metal spin orbit couplers will be used to induce optical coupling into triplet excitonic states, thereby expanding the absorption spectrum into the near infrared. Absorption into the triplet state will give a direct measurement of singlet/triplet spacing, while dissociation of triplet exciton states will provide the relative triplet to singlet dissociation rate. Spin-orbit coupling strengths will be determined as a function of magnetization and spin orientation. Additionally, incorporation of piezoelectric polymers will be used to create a built-in electric field, and thereby alter the excitonic spectrum. This is expected to shift the absorption to the infra-red, or increase the capture efficiency of the photo-excited carriers. The charge dissociation process will be measured using a capacitive photocurrent technique that detects optical absorption combined with physical separation of excited charge. This provides the ability to distinguish between excitonic and free carrier states, to determine excitonic binding energies and recombination efficiencies and the influence of interface materials and conditions on exciton formation and dissociation. Non-Technical. The project addresses fundamental research issues in a topical area of electronic/photonic materials science having technological relevance. There is potential that the research could substantially impact the development of improved and less expensive solar cells. The increased understanding of the conditions necessary for efficient exciton dissociation in organic materials provided by this study may establish a pathway for developing a low-cost, commercially viable organic solar cell technology. Research opportunities are being provided for graduate, undergraduate, and high school students with an emphasis on recruiting women and other under-represented groups. A new undergraduate course on advance device concepts is being introduced, and will include the research strategies being proposed here. Local high school teachers will be introduced to research and trained in experimental techniques so that they will be able to develop research modules to present to their students. The idea is to introduce high school students to the excitement of energy conversion science, and encourage them to pursue careers in science and engineering.
