Determining the role of polymer molecular weight for high-performance all-polymer solar cells: Its effect on polymer aggregation and phase separation

Hyunbum Kang, Mohammad Afsar Uddin, Changyeon Lee, Ki Hyun Kim, Thanh Luan Nguyen, Wonho Lee, Yuxiang Li, Cheng Wang, Han Young Woo, Bumjoon J. Kim

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223 Citations (Scopus)

Abstract

The molecular weight of a conjugated polymer is one of the key factors determining the electrical, morphological, and mechanical properties as well as its solubility in organic solvents and miscibility with other polymers. In this study, a series of semicrystalline poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) polymers with different number-average molecular weights (Mns) (PPDT2FBTL, Mn = 12 kg/mol; PPDT2FBTM, Mn= 24 kg/mol; PPDT2FBTH, Mn= 40 kg/mol) were synthesized, and their photovoltaic properties as electron donors for all-polymer solar cells (all-PSCs) with poly[[N,N-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5-(2,2-bithiophene)] (P(NDI2OD-T2)) acceptor were studied. The Mn effect of PPDT2FBT on the structural, morphological, electrical, and photovoltaic properties was systematically investigated. In particular, tuning the Mn induced dramatic effects on the aggregation behaviors of the polymers and their bulk heterojunction morphology of all-PSCs, which was thoroughly examined by grazing incident X-ray scattering, resonant soft X-ray scattering, and other microscopy measurements. High Mn PPDT2FBTH promoted a strong "face-on" geometry in the blend film, suppressed the formation of an excessively large crystalline domain, and facilitated molecularly intermixed phases with P(NDI2OD-T2). Therefore, the optimized all-PSCs based on PPDT2FBTH/P(NDI2OD-T2) showed substantially higher hole and electron mobilities than those of PPDT2FBTL/P(NDI2OD-T2), leading to a power conversion efficiency exceeding 5%, which is one of the highest values for all-PSCs reported thus far.

Original languageEnglish
Pages (from-to)2359-2365
Number of pages7
JournalJournal of the American Chemical Society
Volume137
Issue number6
DOIs
Publication statusPublished - 2015 Feb 18
Externally publishedYes

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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