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The Nonequilibrium Dynamics of Electrons and Holes in Disordered Molecular Semiconductors

Event Details

Event Dates: 

Friday, April 6, 2018 - 4:00pm

Seminar Location: 

  • JILA Auditorium

Speaker Name(s): 

Adam Willard

Speaker Affiliation(s): 

Massachusetts Institute of Technology
Seminar Type/Subject

Scientific Seminar Type: 

  • Phys Chem/Chem Phys Seminar

Event Details & Abstract: 

One of the fundamental microscopic processes in photocurrent generation is the dissociation of neutral photo-excitations (i.e., Frenkel excitons) into free charge carriers (i.e., electrons and holes). This process requires the physical separation of oppositely charged electrons and holes, which are held together by an attractive electrostatic binding energy. In traditional inorganic-based photovoltaic materials, this binding energy is generally small and easily overcome, however, in organic-based photovoltaics the exciton binding energy can significantly exceed thermal energies. The inability of bound charges to overcome this large binding energy has been implicated as a primary source of efficiency loss in OPVs. Here I present results from our recent efforts to explore the role of static molecular disorder in mediating this process. Using a simple lattice model of exciton dynamics we simulate the microscopic dynamics of interface exciton states. We show that the presence of slowly evolving spatial energetic disorder (due for example to variations in nuclear configuration) can enhance the dissociation process. We highlight that the mechanism for this enhancement involves the nonequilibrium dynamics of the electron and hole and thus cannot be understood solely in terms of thermodynamics. This, therefore, demonstrates the importance of considering nonequilibrium effects in the modeling and design of organic electronic systems.

Research Site: http://willardgroup.mit.edu/index.html