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Abstract
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Distinct multi-thermal treatments comprising cycling, aging, and seeding were introduced to prepare very thick
bulk heterojunction (BHJ) active layers (ca. 800 nm) of poly(3-hexylthiophene) (P3HT):phenyl-C71-butyric
acid methyl ester (PC71BM) photovoltaic cells. To this end, various P3HT48800-based rod-coil block copolymers
having the coily blocks of polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(ethylene glycol)
(PEG) were synthesized. The grazing incidence X-ray scattering,field emission scanning electron microscopy
(FESEM), and transmission electron microscopy (TEM) analyses proved that the dielectric coily blocks, which
were excluded from the P3HT crystalline structure, accumulated on the crystals surface without decreasing the
crystal quality and formed hairy crystals. The multi-thermal techniques facilitated stacking of the growth planes
in π-π direction for the P3HT crystals, thereby, this dimension was improved from 5 to 27 nm for
conventionally prepared BHJs to 53–265 nm for multi-thermally developed ones. The hydrophobic coily blocks
were capable of neutralizing the influence of the PCBM molecules presence in the growth environment, which
resulted in the larger P3HT crystals in a similar condition. By switching the conventional spin coating approach
to the cycling, aging, and seeding methods, the P3HT crystals and the PCBM clusters were gradually coarsened
and the respectived-spacings decreased. This trend enhanced the hole mobility (=8.8×10
−5
cm
2
/Vs), electron
mobility (=2.5×10
−3
cm
2
/Vs), short circuit current density (Jsc=12.02 mA/cm
2
), fill factor (FF=69%), and
power conversion efficiency (PCE=4.39%) up to the maximum values for seeding approach. Moreover, the
higher percentages of face-on orientation were detected in the BHJs with lowerd-spacings in the hexyl side
chain direction. Hairy P3HT48800-b-PS crystals developed by seeding method possessed the highest face-on
orientation (~5.5%).
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