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



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


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).
Journal of Materials Chemistry A


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


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], (Accessed July 15, 2024)


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Created November 1, 2022, Updated March 18, 2023