title: Direct Correlation of Charge Transfer Absorption with Molecular Donor:Acceptor Interfacial Area via Photothermal Deflection Spectroscopy.
abstract: Here we show that the charge transfer (CT) absorption signal in bulk-heterojunction solar cell blends, measured by photothermal deflection spectroscopy, is directly proportional to the density of molecular donor:acceptor interfaces. Since the optical transitions from the ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both the 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 as 0.3 D and the electronic coupling between the ground and CT states to be on the order of 30 meV.
authors: †Department of Materials and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.|‡Division of Physical Sciences and Engineering, Solar and Photovoltaic Engineering Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
authors: Ester
authors: E
authors: Buchaca-Domingo
authors: §Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.|∥Institut für Angewandte Photophysik, TU Dresden, 01069 Dresden, Germany.
authors: Koen
authors: K
authors: Vandewal
authors: ⊥Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.
authors: Zhuping
authors: Z
authors: Fei
authors: #CSIRO Manufacturing Flagship, Clayton, VIC 3169, Australia.
authors: Scott E
authors: SE
authors: Watkins
authors: #CSIRO Manufacturing Flagship, Clayton, VIC 3169, Australia.
authors: Fiona H
authors: FH
authors: Scholes
authors: ⊥Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.
authors: James H
authors: JH
authors: Bannock
authors: ⊥Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.
authors: John C
authors: JC
authors: de Mello
authors: ∇National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, United States.
authors: Lee J
authors: LJ
authors: Richter
authors: ∇National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, United States.
authors: Dean M
authors: DM
authors: DeLongchamp
authors: ‡Division of Physical Sciences and Engineering, Solar and Photovoltaic Engineering Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
authors: Aram
authors: A
authors: Amassian
authors: ⊥Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.
authors: Martin
authors: M
authors: Heeney
authors: §Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.
authors: Alberto
authors: A
authors: Salleo
authors: †Department of Materials and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.
authors: Natalie
authors: N
authors: Stingelin