@article{LangeBlakesleyFrischetal.2011,
  author    = {Lange, Ilja and Blakesley, James C. and Frisch, Johannes and Vollmer, Antje and Koch, Norbert and Neher, Dieter},
  title     = {Band bending in conjugated polymer layers},
  series = {Physical review letters},
  volume    = {106},
  journal   = {Physical review letters},
  number    = {21},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {0031-9007},
  doi       = {10.1103/PhysRevLett.106.216402},
  pages     = {4},
  year      = {2011},
  abstract  = {We use the Kelvin probe method to study the energy-level alignment of four conjugated polymers deposited on various electrodes. Band bending is observed in all polymers when the substrate work function exceeds critical values. Through modeling, we show that the band bending is explained by charge transfer from the electrodes into a small density of states that extends several hundred meV into the band gap. The energetic spread of these states is correlated with charge-carrier mobilities, suggesting that the same states also govern charge transport in the bulk of these polymers.},
  language  = {en}
}
@article{KniepertSchubertBlakesleyetal.2011,
  author    = {Kniepert, Juliane and Schubert, Marcel and Blakesley, James C. and Neher, Dieter},
  title     = {Photogeneration and recombination in P3HT/PCBM solar cells probed by time-delayed collection field experiments},
  series = {The journal of physical chemistry letters},
  volume    = {2},
  journal   = {The journal of physical chemistry letters},
  number    = {7},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1948-7185},
  doi       = {10.1021/jz200155b},
  pages     = {700 -- 705},
  year      = {2011},
  abstract  = {Time-delayed collection field (TDCF) experiments are performed on bulk heterojunction solar cells comprised of a blend of poly(3-hexylthiophene) and [6,6]-phenyl C-71 butyric acid methyl ester. TDCF is analogous to a pump-probe experiment using optical excitation and an electrical probe with a resolution of < 100 ns. The number of free charge carriers extracted after a short delay is found to be independent of the electric field during illumination. Also, experiments performed with a variable delay between the optical excitation and the electrical probe do not reveal any evidence for the generation of charge via field-assisted dissociation of bound long-lived polaron pairs. Photocurrent transients are well fitted by computational drift diffusion simulations with only direct generation of free charge carriers. With increasing delay times between pump and probe, two loss mechanisms are identified; first, charge-carriers are swept out of the device by the internal electric field, and second, bimolecular recombination of the remaining carriers takes place with a reduced recombination coefficient.},
  language  = {en}
}
@article{BlakesleySchubertSteyrleuthneretal.2011,
  author    = {Blakesley, James C. and Schubert, Marcel and Steyrleuthner, Robert and Chen, Zhihua and Facchetti, Antonio and Neher, Dieter},
  title     = {Time-of-flight measurements and vertical transport in a high electron-mobility polymer},
  series = {Applied physics letters},
  volume    = {99},
  journal   = {Applied physics letters},
  number    = {18},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0003-6951},
  doi       = {10.1063/1.3657827},
  pages     = {3},
  year      = {2011},
  abstract  = {We investigate charge transport in a high-electron mobility polymer, poly(N, N-bis 2-octyldodecyl-naphthalene-1,4,5,8-bis dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) [P(NDI2OD-T2), Polyera ActivInk (TM) N2200]. Time-of-flight measurements reveal electron mobilities approaching those measured in field-effect transistors, the highest ever recorded in a conjugated polymer using this technique. The modest temperature dependence and weak dispersion of the transients indicate low energetic disorder in this material. Steady-state electron-only current measurements reveal a barrier to injection of about 300 meV. We propose that this barrier is located within the P(NDI2OD-T2) film and arises from molecular orientation effects.},
  language  = {en}
}
@article{BlakesleyNeher2011,
  author    = {Blakesley, James C. and Neher, Dieter},
  title     = {Relationship between energetic disorder and open-circuit voltage in bulk heterojunction organic solar cells},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {84},
  journal   = {Physical review : B, Condensed matter and materials physics},
  number    = {7},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1098-0121},
  doi       = {10.1103/PhysRevB.84.075210},
  pages     = {12},
  year      = {2011},
  abstract  = {We simulate organic bulk heterojunction solar cells. The effects of energetic disorder are incorporated through a Gaussian or exponential model of density of states. Analytical models of open-circuit voltage (V(OC)) are derived from the splitting of quasi-Fermi potentials. Their predictions are backed up by more complex numerical device simulations including effects such as carrier-density-dependent charge-carrier mobilities. It is predicted that the V(OC) depends on: (1) the donor-acceptor energy gap; (2) charge-carrier recombination rates; (3) illumination intensity; (4) the contact work functions (if not in the pinning regime); and (5) the amount of energetic disorder. A large degree of energetic disorder, or a high density of traps, is found to cause significant reductions in V(OC). This can explain why V(OC) is often less than expected in real devices. Energetic disorder also explains the nonideal temperature and intensity dependence of V(OC) and the superbimolecular recombination rates observed in many real bulk heterojunction solar cells.},
  language  = {en}
}