title: Molecular weight effect on the efficiency of polymer solar cells.
abstract: In this study, we report the investigation of the influence of molecular weight (MW) on power conversion efficiency (PCE) of bulk heterojunction (BHJ) polymer solar cells (PSCs). It was found that PCEs of PSCs fabricated by poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) blended with [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) as the active layer, are significantly enhanced from 5.41 to 6.27 and 8.50% along with the MW of PTB7 increased from 18 to 40 and 128 kg/mol, respectively. This enhancement is attributed to the enhanced light absorption and increased charge carrier mobility of PTB7 with high MW, and a proper phase separation in BHJ composite of PTB7:PC71BM interpenetrating network. All these results demonstrate that the MW of donor polymer plays an important role in the performance of BHJ PSCs.
authors.affiliation: College of Polymer Science and Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.forename: Kai
authors.initials: K
authors.lastname: Wang
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Hu
authors.forename: Yali
authors.initials: Y
authors.lastname: Yang
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Hsu
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Steven
authors.initials: S
authors.lastname: Xiao
authors.forename: Xiong
authors.initials: X
authors.lastname: Gong
authors.forename: Yong
authors.initials: Y
authors.lastname: Cao