Charge Photogeneration and Recombination in Organic Semiconductors

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The goal of this project is to gain fundamental understanding of charge photogeneration and recombination in organic semiconductors. The approach is to use fresh experimental approaches designed to answer basic questions and to provide mechanistic insight. A time delayed field collection technique will be used to quantify charge generation in conjugated polymers without the ambiguities of photoconductivity or spectroscopic measurements. Theories for the wavelength, field and temperature dependence of charge generation yield will be tested. Transient pump and dump experiments that address the mechanism of charge generation are included. To study recombination, time-gated and thermally stimulated luminescence will be used to interrogate recombination of photogenerated charges that have lost spin correlation. This approach makes the results relevant to electroluminescent devices but is free from the difficulties of quenching at contacts and freezeout of transport at low temperature. %%% An important impact of the project is in education and human resource development through the integration of research and education. The project involves graduate and undergraduate students, including visiting summer students from a minority serving institution, CCNY, with undergraduates doing senior theses taking part in our research. The PI is also active in outreach activities hosting high school students to do research. Participants at all levels will present their work orally and in writing as a part of their experience and to disseminate knowledge obtained in the research. The PI and students also interact with several retired and active industrial colleagues who participate in group research. Their input assists connections to technologically relevant issues where basic research can have important impact. One such thrust is to improve understanding of charge photogeneration in conjugated polymers as it pertains to development of solar cells and photovoltaics based on organic materials. A similar goal is to identify the states resulting from recombination of charges with uncorrelated spins as it pertains to selection of materials for polymer LEDs.***