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

Ester Domingo, Koen Vandewal, Zhuping Fei, Scott E. Watkins, Fiona H. Scholes, James H Bannock, John de Mello, Lee J. Richter, Dean M. DeLongchamp, Aram Amassian, Martin Heeney, Alberto Salleo, Natalie Stingelin

Research output: Contribution to journalArticlepeer-review

39 Scopus citations

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.
Original languageEnglish (US)
Pages (from-to)5256-5259
Number of pages4
JournalJournal of the American Chemical Society
Volume137
Issue number16
DOIs
StatePublished - Apr 16 2015

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