@article{TokmoldinVollbrechtHosseinietal.2021,
  author    = {Tokmoldin, Nurlan and Vollbrecht, Joachim and Hosseini, Seyed Mehrdad and Sun, Bowen and Perdig{\´o}n-Toro, Lorena and Woo, Han Young and Zou, Yingping and Neher, Dieter and Shoaee, Safa},
  title     = {Explaining the fill-factor and photocurrent losses of nonfullerene acceptor-based solar cells by probing the long-range charge carrier diffusion and drift lengths},
  series = {Advanced energy materials},
  volume    = {11},
  journal   = {Advanced energy materials},
  number    = {22},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {1614-6840},
  doi       = {10.1002/aenm.202100804},
  pages     = {9},
  year      = {2021},
  abstract  = {Organic solar cells (OSC) nowadays match their inorganic competitors in terms of current production but lag behind with regards to their open-circuit voltage loss and fill-factor, with state-of-the-art OSCs rarely displaying fill-factor of 80\% and above. The fill-factor of transport-limited solar cells, including organic photovoltaic devices, is affected by material and device-specific parameters, whose combination is represented in terms of the established figures of merit, such as theta and alpha. Herein, it is demonstrated that these figures of merit are closely related to the long-range carrier drift and diffusion lengths. Further, a simple approach is presented to devise these characteristic lengths using steady-state photoconductance measurements. This yields a straightforward way of determining theta and alpha in complete cells and under operating conditions. This approach is applied to a variety of photovoltaic devices-including the high efficiency nonfullerene acceptor blends-and show that the diffusion length of the free carriers provides a good correlation with the fill-factor. It is, finally, concluded that most state-of-the-art organic solar cells exhibit a sufficiently large drift length to guarantee efficient charge extraction at short circuit, but that they still suffer from too small diffusion lengths of photogenerated carriers limiting their fill factor.},
  language  = {en}
}
@article{RyllSchmitzdeBooretal.2018,
  author    = {Ryll, Britta and Schmitz, Andreas and de Boor, Johannes and Franz, Alexandra and Whitfield, Pamela S. and Reehuis, Manfred and Hoser, Andreas and M{\"u}ller, Eckhard and Habicht, Klaus and Fritscht, Katharina},
  title     = {Structure, phase composition, and thermoelectric properties of YbxCo4Sb12 and their dependence on synthesis method},
  series = {ACS applied energy materials},
  volume    = {1},
  journal   = {ACS applied energy materials},
  number    = {1},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {2574-0962},
  doi       = {10.1021/acsaem.7b00015},
  pages     = {113 -- 122},
  year      = {2018},
  abstract  = {We present a combined microscopic and macroscopic study of YbxCo4Sb12 skutterudites for a range of nominal filling fractions, 0.15 < x < 0.75. The samples were synthesized using two different methods — a melt-quench-annealing route in evacuated quartz ampoules and a non-equilibrium ball-mill route — for which we directly compare the crystal structure and phase composition as well as the thermoelectric properties. Rietveld refinements of high-quality neutron powder diffraction data reveal about a 30-40\% smaller Yb occupancy on the crystallographic 2a site than nominally expected for both synthesis routes. We observe a maximum filling fraction of at least 0.439(7) for a sample synthesized by the ball-mill routine, exceeding theoretical predictions of the filling fraction limit of 0.2-0.3. A single secondary phase of CoSb2 is observed in ball-mill-synthesized samples, while two secondary phases, CoSb2 and YbSb2, are detected for samples prepared by the ampoule route. A detrimental influence of the secondary phases on the thermoelectric properties is observed for secondary-phase fractions larger than 8 wt \% regardless of the kind of secondary phase. The largest figure of merit of all samples with a ZT ∼ 1.0 at 723 K is observed for the sample with a refined Yb content of x2a = 0.159(3), synthesized by the ampoule route.},
  language  = {en}
}