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Open Access Publications from the University of California

Double doping of conjugated polymers with monomer molecular dopants.

  • Author(s): Kiefer, David
  • Kroon, Renee
  • Hofmann, Anna I
  • Sun, Hengda
  • Liu, Xianjie
  • Giovannitti, Alexander
  • Stegerer, Dominik
  • Cano, Alexander
  • Hynynen, Jonna
  • Yu, Liyang
  • Zhang, Yadong
  • Nai, Dingqi
  • Harrelson, Thomas F
  • Sommer, Michael
  • Moulé, Adam J
  • Kemerink, Martijn
  • Marder, Seth R
  • McCulloch, Iain
  • Fahlman, Mats
  • Fabiano, Simone
  • Müller, Christian
  • et al.

Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.

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