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Quantitative correlation of the effects of crystallinity and additive on nanomorphology and solar cell performance of isoindigo-based copolymers

Abstract

The high power conversion efficiency of bulk heterojunction (BHJ) polymer solar cell can be fabricated from either low crystallinity (P3TI) or high crystallinity (P6TI) of isoindigo-based donor-acceptor alternating copolymers blended with PC71BM by controlling nanophase separation using additive. The P3TI shows similar device performance regardless the type of additives, while the P6TI is significantly affected by the additive being aliphatic or aromatic. To understand the interplays of crystallinity of polymer and type of additive on the formation of nanomorphology of BHJ, we employed the simultaneous grazing-incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS) technique to do the quantitative investigation. By incorporating additive, the PC71BM molecules can be easily intercalated into the P3TI polymer-rich domain and the size of PC71BM clusters is reduced from about 24 nm to about 5 nm by either aliphatic 1,8-diiodooctane (DIO) or aromatic 1-chloronaphthalene (CN). By comparison, the PC71BM molecules are more difficult to be intercalated into high crystalline P6TI dense domain and the PC71BM molecules have higher tendency to be self-aggregated which result in a larger size of PC71BM clusters about 58 nm. The clusters can be reduced to about 7 nm by DIO and 13 nm by CN. The presence of crystallites in P6TI domain can interact with the additive to tailor the crystallization of PC71BM clusters to be in the similar size with P6TI crystallites (~12 nm) and form the connected network for efficient charge transportation. Thus, the power conversion efficiency of P6TI:PC71BM reaches its maximum of 7.04% by using aromatic CN additive. This is a new finding phenomenon of crystallinity effect which does not observe in the common low crystalline donor-acceptor alternating copolymers such as PTB7. Our results provide a useful guideline to manipulate the desired morphology of BHJ film constructed from alternating copolymer with different crystallinity, which is critical for achieving high power conversion efficiency of solar cells.

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Supplementary files

Publication details

The article was received on 23 Jun 2017, accepted on 07 Aug 2017 and first published on 08 Aug 2017


Article type: Paper
DOI: 10.1039/C7CP04238H
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Quantitative correlation of the effects of crystallinity and additive on nanomorphology and solar cell performance of isoindigo-based copolymers

    C. Chang, Y. Huang, C. Tsao, C. Chen, C. Su and W. Su, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP04238H

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