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OSE Seminar with Dr. John Grey on resolving multi-excitonic interactions in single conjugated polymer chains

Departmental News

John Grey

Posted: August 24, 2018

Wednesday, August 29, 2018
CHTM, Room 101
The advent of multiple exciton generation mechanisms has generated intense interest for improving light harvesting ability for solar cells based on excitonic materials.  Conjugated organic molecules represent an important component of this effort where the generation of two excitons per absorbed photon has been reported for a number of small molecule systems.  Because of fundamental limitations on the overall yield of multiplication, larger conjugated polymers are being pursued as multi-exciton generating materials that may be processed from solution and have a broad range of synthetic tunability.  However, the multi-chromophoric nature of polymers coupled with extreme conformational heterogeneity present a formidable challenge for understanding and eventually controlling excitonic population dynamics of different spin to optimize performance at the materials level.  We use a specialized form of single molecule spectroscopy to resolve the presence of multiple excitonic species and their interactions over a broad range of time scales.  Our approach avoids complications encountered in condensed functional forms by spatially confining excitonic interactions to single polymer chains.  We then use a stochastic photodynamic model to describe population dynamics that enables the extraction of key multi-exciton interaction rate constants.  We propose this approach can help bridge the gap in understanding exciton interactions between the molecular to materials levels.