Visualization of multi-orientational ordering within a single domain of donor non-fullerene acceptor blends

Published

November 1, 2022

Author(s)

Eliot Gann, Christopher McNeill, Urvashi Bothra, Pramiti Hui, Wen Liang Tanc, Hariprasad Venugopal, Chandramouli Subramaniam, Amelia C.Y. Liu, Dinesh Kabra

Abstract

We have studied the tailored micron-scale phase-separated bulk heterojunction (BHJ) morphology of the well-known polymer (PTB7-Th) and a narrow bandgap acceptor 2,2'-[[4,4,9,9-Tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno [1,2-b:5,6-b']dithiophene-2,7-diyl]bis]] [[4-[(2-ethylhexyl)oxy]-5,2-thiophenediyl] methylidyne(5,6-difluoro-3-oxo-1H-indene-2,1(3H)-diylidene) ]]bis[propanedinitrile] (IEICO-4F) based blend systems. The BHJ morphology of the PTB7-Th:IEICO-4F in chlorobenzene (CB) with 3 vol% of 1-chloronaphthalene (CN) drastically changed from large micron-sized circular phase-separated domains to fine nano-domains when either the speed or duration of spin coating was changed. Interestingly, we observed a decrease in oscillator strength corresponding to IEICO-4F for the coarse blend film compared to the fine blend film, which we explained using structural studies. From micro-Raman spectroscopic studies, we found that the circular domains were rich in IEICO-4F, and the matrix was rich in the PTB7-Th for the coarse phase-separated films. Moreover, for these films we observed a signature of vertical phase separation within the domains. We visualized the molecular orientation of the PTB7-Th:IEICO-4F blend systems by combining x-ray scattering structural studies and cryo-electron microscopy (EM). Unexpectedly, the molecules oriented differently at the edge and the center of the domains, as observed from cryo-EM. This feature has not been observed previously in spin-coated non-fullerene acceptors (NFAs). Furthermore, we observed that the processing conditions affect the morphology drastically but this effect on the device performance is comparatively lower than observed for classically known donor-fullerene based blends in the domain of organic photovoltaics (OPV).

Citation

Journal of Materials Chemistry A

Pub Type

Journals

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Keywords

non-fullerene acceptors, phase-separated morphology, cryo-EM, micro-Raman spectroscopy, multi-orientational packing

Citation

Gann, E. , McNeill, C. , Bothra, U. , Hui, P. , Tanc, W. , Venugopal, H. , Subramaniam, C. , C.Y. Liu, A. and Kabra, D. (2022), Visualization of multi-orientational ordering within a single domain of donor non-fullerene acceptor blends, Journal of Materials Chemistry A, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=933137 (Accessed April 25, 2024)