title: Mobility-controlled performance of thick solar cells based on fluorinated copolymers.
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 structure-property 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.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Wentao
authors.initials: W
authors.lastname: Li
authors.forename: Steve
authors.initials: S
authors.lastname: Albrecht
authors.forename: Liqiang
authors.initials: L
authors.lastname: Yang
authors.forename: Steffen
authors.initials: S
authors.lastname: Roland
authors.forename: John R
authors.initials: JR
authors.lastname: Tumbleston
authors.forename: Terry
authors.initials: T
authors.lastname: McAfee
authors.forename: Liang
authors.initials: L
authors.lastname: Yan
authors.forename: Mary Allison
authors.initials: MA
authors.lastname: Kelly
authors.forename: Harald
authors.initials: H
authors.lastname: Ade
authors.forename: Dieter
authors.initials: D
authors.lastname: Neher
authors.forename: Wei
authors.initials: W
authors.lastname: You