Direct correlation of charge transfer absorption with molecular donor:acceptor interfacial area via photothermal deflection spectroscopy

Abstract
We show that the Charge Transfer (CT) absorption signal in bulk-heterojunction (BHJ) solar cell blends, measured by photothermal deflection spectroscopy (PDS), is directly proportional to the density of molecular donor/acceptor interfaces. Since the optical transitions from ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both donor and acceptor, we can exploit the use of this sensitive linear absorption spectroscopy for such quantification. Moreover, we determine the absolute molar extinction coefficient of the CT transition for an archetypical polymer-fullerene interface. The latter is ~100 times lower than the extinction coefficient of the donor chromophore involved, allowing us to experimentally estimate the transition dipole moment (0.3 D) and the electronic coupling between ground state and CT state to be on the order of 30 meV.

Citation
Direct correlation of charge transfer absorption with molecular donor:acceptor interfacial area via photothermal deflection spectroscopy 2015:150409144253004 Journal of the American Chemical Society

Publisher
American Chemical Society (ACS)

Journal
Journal of the American Chemical Society

DOI
10.1021/ja512410f

PubMed ID
25856143

Additional Links
http://pubs.acs.org/doi/abs/10.1021/ja512410f

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