title: Short-lived charge-transfer excitons in organic photovoltaic cells studied by high-field magneto-photocurrent.
abstract: The main route of charge photogeneration in efficient organic photovoltaic cells based on bulk hetero-junction donor-acceptor blends involves short-lived charge-transfer excitons at the donor-acceptor interfaces. The cell efficiency is critically affected by the charge-transfer exciton recombination and dissociation processes. By measuring the magneto-photocurrent under ambient conditions at room temperature, we show here that magnetic field-induced spin-mixing among the charge-transfer exciton spin sublevels occurs in fields up to at least 8.5 Tesla. The resulting magneto-photocurrent increases at high fields showing non-saturating behaviour up to the highest applied field. We attribute the observed high-field spin-mixing mechanism to the difference in the donor-acceptor g-factors. The non-saturating magneto-photocurrent response at high field indicates that there exist charge-transfer excitons with lifetime in the sub-nanosecond time domain. The non-Lorentzian high-field magneto-photocurrent response indicates a dispersive decay mechanism that originates due to a broad distribution of charge-transfer exciton lifetimes.
authors: 1] Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel [2].
authors: Ayeleth H
authors: AH
authors: Devir-Wolfman
authors: 1] Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel [2].
authors: Bagrat
authors: B
authors: Khachatryan
authors: 1] Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA [2].
authors: Bhoj R
authors: BR
authors: Gautam
authors: Department of Electrical and Computer Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors: Lior
authors: L
authors: Tzabary
authors: Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors: Amit
authors: A
authors: Keren
authors: Department of Electrical and Computer Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors: Nir
authors: N
authors: Tessler
authors: Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA.
authors: Z Valy
authors: ZV
authors: Vardeny
authors: Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel.
authors: Eitan
authors: E
authors: Ehrenfreund