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Importance of 2D Conjugated Side Chains of Benzodithiophene-Based Polymers in Controlling Polymer Packing, Interfacial Ordering, and Composition Variations of All-Polymer Solar Cells

We delineate the important role of 2D conjugated alkylthiophene side chains of polymers in manipulating the molecular orientation and ordering at the polymer donor/polymer acceptor (PD/PA) interface as well as the composition variations in the blend active layer of all-polymer solar cells (all-PSCs). To systematically investigate the impact of 2D conjugated side chains on the performance of all-PSCs, we synthesized a series of poly(benzo[1,2-b:4,5-b̀]-dithiophene-thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymer donors with different contents of alkoxy and alkylthiophene side chains, from 0 to 100% (PBDT-TPD (P1, 100% alkoxy side chain), PBDTT0.29-TPD (P2), PBDTT0.59-TPD (P3), PBDTT0.76-TPD (P4), and PBDTT-TPD (P5, 100% alkylthiophene side chain).

Research by:

  • Changyeon Lee
  • Thota Giridhar
  • Joonhyeong Choi
  • Seonha Kim
  • Youngwoong Kim
  • Taesu Kim
  • Wonho Lee
  • Han-Hee Cho
  • Cheng Wang
  • Harald Ade
  • Bumjoon J. Kim

Abstract:

We delineate the important role of 2D conjugated alkylthiophene side chains of polymers in manipulating the molecular orientation and ordering at the polymer donor/polymer acceptor (PD/PA) interface as well as the composition variations in the blend active layer of all-polymer solar cells (all-PSCs). To systematically investigate the impact of 2D conjugated side chains on the performance of all-PSCs, we synthesized a series of poly(benzo[1,2-b:4,5-b̀]-dithiophene-thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymer donors with different contents of alkoxy and alkylthiophene side chains, from 0 to 100% (PBDT-TPD (P1, 100% alkoxy side chain), PBDTT0.29-TPD (P2), PBDTT0.59-TPD (P3), PBDTT0.76-TPD (P4), and PBDTT-TPD (P5, 100% alkylthiophene side chain). The P1–P5 polymer donors produced similar PCEs of ∼6% in fullerene-based PSCs. In contrast, for the all-PSC systems, the changes in the side chain composition of the polymers induced a strong increasing trend in the power conversion efficiencies (PCEs), from 2.82% (P1), to 3.16% (P2), to 4.41% (P3), to 5.32% (P4), and to 6.60% (P5). The significant increase in the PCEs of the all-PSCs was attributed mainly to improvements in the short-circuit current density (JSC) and fill factor (FF). The 2D conjugated side chains promoted localized molecular orientation and ordering relative to the PD/PA interfaces and improved domain purity, which led to enhanced exciton dissociation and charge transport characteristics of the all-PSCs. Our observations highlight the advantage of incorporating 2D conjugated side chains into polymer donors for producing high-performance all-PSC systems.

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Citation:

Lee, C., Giridhar, T., Choi, J., Kim, S., Kim, Y., Kim, T., … Kim, B. J. (2017). Importance of 2D Conjugated Side Chains of Benzodithiophene-Based Polymers in Controlling Polymer Packing, Interfacial Ordering, and Composition Variations of All-Polymer Solar Cells. Chemistry of Materials, 29(21), 9407–9415. https://doi.org/10.1021/acs.chemmater.7b03495