@article{KellyRolandZhangetal.2017,
  author    = {Kelly, Mary Allison and Roland, Steffen and Zhang, Qianqian and Lee, Youngmin and Kabius, Bernd and Wang, Qing and Gomez, Enrique D. and Neher, Dieter and You, Wei},
  title     = {Incorporating Fluorine Substitution into Conjugated Polymers for Solar Cells},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {121},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {4},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.6b10993},
  pages     = {2059 -- 2068},
  year      = {2017},
  abstract  = {Fluorinating conjugated polymers is a proven strategy for creating high performance materials in polymer solar cells, yet few studies have investigated the importance of the fluorination method. We compare the performance of three fluorinated systems: a poly(benzodithieno-dithienyltriazole) (PBnDT-XTAZ) random copolymer where 50\% of the acceptor units are difluorinated, PBnDT-mFTAZ where every acceptor unit is monofluorinated, and a 1:1 physical blend of the difluorinated and nonfluorinated polymer. All systems have the same degree of fluorination (50\%) yet via different methods (chemically vs physically, random vs regular). We show that these three systems have equivalent photovoltaic behavior:,similar to 5.2\% efficiency with a short-circuit current (J(sc)) at,similar to 11 mA cm(-2), an open-circuit voltage (v(oc)) at 0.77 V, and a fill factor (FF) of similar to 60\%. Further investigation of these three systems demonstrates that the charge generation, charge extraction, and charge transfer state are essentially identical for the three studied systems. Transmission electron microscopy shows no significant differences in the morphologies. All these data illustrate that it is possible to improve performance not only via regular or random fluorination but also by physical addition via a ternary blend. Thus, our results demonstrate the versatility of incorporating fluorine in the active layer of polymer solar cells to enhance device performance.},
  language  = {en}
}
@article{LiAbrechtYangetal.2014,
  author    = {Li, Wentao and Abrecht, Steve and Yang, Liqiang and Roland, Steffen and Tumbleston, John R. and McAfee, Terry and Yan, Liang and Kelly, Mary Allison and Ade, Harald W. and Neher, Dieter and You, Wei},
  title     = {Mobility-controlled performance of thick solar cells based on fluorinated copolymers},
  series = {Journal of the American Chemical Society},
  volume    = {136},
  journal   = {Journal of the American Chemical Society},
  number    = {44},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0002-7863},
  doi       = {10.1021/ja5067724},
  pages     = {15566 -- 15576},
  year      = {2014},
  abstract  = {Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structureproperty relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by mass production technologies.},
  language  = {en}
}