@article{GoelSiegertKraussetal.2020,
  author    = {Goel, Mahima and Siegert, Marie and Krauss, Gert and Mohanraj, John and Hochgesang, Adrian and Heinrich, David C. and Fried, Martina and Pflaum, Jens and Thelakkat, Mukundan},
  title     = {HOMO-HOMO Electron Transfer: An Elegant Strategy for p-Type Doping of Polymer Semiconductors toward Thermoelectric Applications},
  series = {Advanced Materials},
  volume    = {32},
  journal   = {Advanced Materials},
  number    = {43},
  doi       = {10.1002/adma.202003596},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217850},
  year      = {2020},
  abstract  = {Unlike the conventional p-doping of organic semiconductors (OSCs) using acceptors, here, an efficient doping concept for diketopyrrolopyrrole-based polymer PDPP[T]\(_{2}\)-EDOT (OSC-1) is presented using an oxidized p-type semiconductor, Spiro-OMeTAD(TFSI)\(_{2}\) (OSC-2), exploiting electron transfer from HOMO\(_{OSC-1}\) to HOMO\(_{OSC-2}\). A shift of work function toward the HOMO\(_{OSC-1}\) upon doping is confirmed by ultraviolet photoelectron spectroscopy (UPS). Detailed X-ray photoelectron spectroscopy (XPS) and UV-vis-NIR absorption studies confirm HOMO\(_{OSC-1}\) to HOMO\(_{OSC-2}\) electron transfer. The reduction products of Spiro-OMeTAD(TFSI)\(_{2}\) to Spiro-OMeTAD(TFSI) and Spiro-OMeTAD is also confirmed and their relative amounts in doped samples is determined. Mott-Schottky analysis shows two orders of magnitude increase in free charge carrier density and one order of magnitude increase in the charge carrier mobility. The conductivity increases considerably by four orders of magnitude to a maximum of 10 S m\(^{-1}\) for a very low doping ratio of 8 mol\%. The doped polymer films exhibit high thermal and ambient stability resulting in a maximum power factor of 0.07 µW m\(^{-1}\) K\(^{-2}\) at a Seebeck coefficient of 140 µV K\(^{-1}\) for a very low doping ratio of 4 mol\%. Also, the concept of HOMO\(_{OSC-1}\) to HOMO\(_{OSC-2}\) electron transfer is a highly efficient, stable and generic way to p-dope other conjugated polymers.},
  language  = {en}
}
@article{GeigerAcharyaReutteretal.2020,
  author    = {Geiger, Michael and Acharya, Rachana and Reutter, Eric and Ferschke, Thomas and Zschieschang, Ute and Weis, J{\"u}rgen and Pflaum, Jens and Klauk, Hagen and Weitz, Ralf Thomas},
  title     = {Effect of the Degree of the Gate-Dielectric Surface Roughness on the Performance of Bottom-Gate Organic Thin-Film Transistors},
  series = {Advanced Materials Interfaces},
  volume    = {7},
  journal   = {Advanced Materials Interfaces},
  number    = {10},
  doi       = {10.1002/admi.201902145},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214830},
  year      = {2020},
  abstract  = {In organic thin-film transistors (TFTs) fabricated in the inverted (bottom-gate) device structure, the surface roughness of the gate dielectric onto which the organic-semiconductor layer is deposited is expected to have a significant effect on the TFT characteristics. To quantitatively evaluate this effect, a method to tune the surface roughness of a gate dielectric consisting of a thin layer of aluminum oxide and an alkylphosphonic acid self-assembled monolayer over a wide range by controlling a single process parameter, namely the substrate temperature during the deposition of the aluminum gate electrodes, is developed. All other process parameters remain constant in the experiments, so that any differences observed in the TFT performance can be confidently ascribed to effects related to the difference in the gate-dielectric surface roughness. It is found that an increase in surface roughness leads to a significant decrease in the effective charge-carrier mobility and an increase in the subthreshold swing. It is shown that a larger gate-dielectric surface roughness leads to a larger density of grain boundaries in the semiconductor layer, which in turn produces a larger density of localized trap states in the semiconductor.},
  language  = {en}
}