@article{HoffmannJaiserHayeretal.2013,
  author    = {Hoffmann, Sebastian T. and Jaiser, Frank and Hayer, Anna and Baessler, Heinz and Unger, Thomas and Athanasopoulos, Stavros and Neher, Dieter and Koehler, Anna},
  title     = {How Do Disorder, Reorganization, and Localization Influence the Hole Mobility in Conjugated Copolymers?},
  series = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY},
  volume    = {135},
  journal   = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY},
  number    = {5},
  publisher = {AMER CHEMICAL SOC},
  address   = {WASHINGTON},
  issn      = {0002-7863},
  doi       = {10.1021/ja308820j},
  pages     = {1772 -- 1782},
  year      = {2013},
  abstract  = {In order to unravel the intricate interplay between disorder effects, molecular reorganization, and charge carrier localization, a comprehensive study was conducted on hole transport in a series of conjugated alternating phenanthrene indenofluorene copolymers. Each polymer in the series contained one further comonomer comprising monoamines, diamines, or amine-free structures, whose influence on the electronic, optical, and charge transport properties was studied. The series covered a wide range of highest occupied molecular orbital (HOMO) energies as determined by cyclovoltammetry. The mobility, inferred from time-of-flight (ToF) experiments as a function of temperature and electric field, was found to depend exponentially on the HOMO energy. Since possible origins for this effect include energetic disorder, polaronic effects, and wave function localization, the relevant parameters were determined using a range of methods. Disorder and molecular reorganization were established first by an analysis of absorption and emission measurements and second by an analysis of the ToF measurements. In addition, density functional theory calculations were carried out to determine how localized or delocalized holes on a polymer chain are and to compare calculated reorganization energies with those that have been inferred from optical spectra. In summary, we conclude that molecular reorganization has little effect on the hole mobility in this system while both disorder effects and hole localization in systems with low-lying HOMOs are predominant. In particular, as the energetic disorder is comparable for the copolymers, the absolute value of the hole mobility at room temperature is determined by the hole localization associated with the triarylamine moieties.},
  language  = {en}
}
@article{ScharsichLohwasserSommeretal.2012,
  author    = {Scharsich, Christina and Lohwasser, Ruth H. and Sommer, Michael and Asawapirom, Udom and Scherf, Ullrich and Thelakkat, Mukundan and Neher, Dieter and Koehler, Anna},
  title     = {Control of aggregate formation in poly(3-hexylthiophene) by solvent, molecular weight, and synthetic method},
  series = {Journal of polymer science : B, Polymer physics},
  volume    = {50},
  journal   = {Journal of polymer science : B, Polymer physics},
  number    = {6},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0887-6266},
  doi       = {10.1002/polb.23022},
  pages     = {442 -- 453},
  year      = {2012},
  abstract  = {Aggregate formation in poly(3-hexylthiophene) depends on molecular weight, solvent, and synthetic method. The interplay of these parameters thus largely controls device performance. In order to obtain a quantitative understanding on how these factors control the resulting electronic properties of P3HT, we measured absorption in solution and in thin films as well as the resulting field effect mobility in transistors. By a detailed analysis of the absorption spectra, we deduce the fraction of aggregates formed, the excitonic coupling within the aggregates, and the conjugation length within the aggregates, all as a function of solvent quality for molecular weights from 5 to 19 kDa. From this, we infer in which structure the aggregated chains pack. Although the 5 kDa samples form straight chains, the 11 and 19 kDa chains are kinked or folded, with conjugation lengths that increase as the solvent quality reduces. There is a maximum fraction of aggregated chains (about 55 +/- 5\%) that can be obtained, even for poor solvent quality. We show that inducing aggregation in solution leads to control of aggregate properties in thin films. As expected, the field-effect mobility correlates with the propensity to aggregation. Correspondingly, we find that a well-defined synthetic approach, tailored to give a narrow molecular weight distribution, is needed to obtain high field effect mobilities of up to 0.01 cm2/Vs for low molecular weight samples (=11 kDa), while the influence of synthetic method is negligible for samples of higher molecular weight, if low molecular weight fractions are removed by extraction.},
  language  = {en}
}