@article{KurpiersFerronRolandetal.2018,
  author    = {Kurpiers, Jona and Ferron, Thomas and Roland, Steffen and Jakoby, Marius and Thiede, Tobias and Jaiser, Frank and Albrecht, Steve and Janietz, Silvia and Collins, Brian A. and Howard, Ian A. and Neher, Dieter},
  title     = {Probing the pathways of free charge generation in organic bulk heterojunction solar cells},
  series = {Nature Communications},
  volume    = {9},
  journal   = {Nature Communications},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2041-1723},
  doi       = {10.1038/s41467-018-04386-3},
  pages     = {11},
  year      = {2018},
  abstract  = {The fact that organic solar cells perform efficiently despite the low dielectric constant of most photoactive blends initiated a long-standing debate regarding the dominant pathways of free charge formation. Here, we address this issue through the accurate measurement of the activation energy for free charge photogeneration over a wide range of photon energy, using the method of time-delayed collection field. For our prototypical low bandgap polymer:fullerene blends, we find that neither the temperature nor the field dependence of free charge generation depend on the excitation energy, ruling out an appreciable contribution to free charge generation though hot carrier pathways. On the other hand, activation energies are on the order of the room temperature thermal energy for all studied blends. We conclude that charge generation in such devices proceeds through thermalized charge transfer states, and that thermal energy is sufficient to separate most of these states into free charges.},
  language  = {en}
}
@article{SiniSchubertRiskoetal.2018,
  author    = {Sini, Gjergji and Schubert, Marcel and Risko, Chad and Roland, Steffen and Lee, Olivia P. and Chen, Zhihua and Richter, Thomas V. and Dolfen, Daniel and Coropceanu, Veaceslav and Ludwigs, Sabine and Scherf, Ullrich and Facchetti, Antonio and Frechet, Jean M. J. and Neher, Dieter},
  title     = {On the Molecular Origin of Charge Separation at the Donor-Acceptor Interface},
  series = {Advanced energy materials},
  volume    = {8},
  journal   = {Advanced energy materials},
  number    = {12},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6832},
  doi       = {10.1002/aenm.201702232},
  pages     = {15},
  year      = {2018},
  abstract  = {Fullerene-based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor-acceptor (D-A) interface. Model systems comprised of polythiophene-based donor and rylene diimide-based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct-contact intermolecular polarization play in establishing a driving force ( energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules.},
  language  = {en}
}