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(a) (b) Energy Science

ACTIVITY REPORT 2016

(c) (d)

Fig. 1: (a) GIWAXS in-plane profiles extracted from the corresponding 2D patterns of active layers of PTB7:PC71BM prepared with
varied routes as indicated. The characteristic PTB7 (100) and PC71BM ordering signals are marked with arrows. (b) 2D GISAXS
patterns of active layers processed without additive and that subjected to a dipping treatment. The much richer scattering fea-
tures marked with squares (with prominent scattering strips highlighted with an arrow in the inset; left) correspond to in-plane
phase-separated and ordered domains of a film processed without additive; these scattering features are largely eliminated
after the dipping treatment (GISAXS pattern at the right side). (c) Corresponding in-plane GISAXS profiles extracted at qz =
0.03 Å fitted (solid curves) respectively with models described in the text. The dotted thick blue and thin green curves de-
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scribe scattering contributions from large and small PC71BM aggregates, respectively. An additional profile is extracted at qz =
0.038 Å and fitted for the in-plane ordering signal at qz = 0.002 Å , also marked in panel (b). (d) Model-fitted GISAXS profiles
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extracted at qz = 0.030 Å-1 for PTB7:PC71BM active layers processed with varied routes indicated. [Reproduced from Ref. 1]

Figure 1(d) shows fitted GISAXS profiles for active was best fitted using finer primary PC 71BM aggre-
layers processed with SH-na additive and that fol- gates of diameter 5.4 nm that further formed frac-
lowed with a dipping treatment to obtain primary tal-like clusters with D f = 2.0 and ξ y = 42 nm. Overall,
and small PC 71BM aggregates. These sizes are smaller the GISAXS/GIWAXS results indicate that DIO dis-
than previous cases processed without additive or persed PC 71BM better than SH-na. Nevertheless, the
with solely a dipping treatment. To account for the dual-functional SH-na is superior as it facilitated not
steeply increased intensity in the low-q region, the only PC 71BM dispersion and percolation on multi-
large PC 71BM aggregates were further modeled to length scales but also PTB7 crystallization.
be interconnected to form fractal-like clusters with
fitted fractal dimension D f = 2.8 or 2.5 and in-plane In summary, new additive SH-na that can serve to
correlation length ξ y = 140 or 100 nm for the active control integrated bulk and surface morphology, via
layer with SH-na additive or that further subject to conventional spin casting followed by a novel dip-
a dipping treatment. After the dipping treatment, ping in a SH-na solution is reported. The improved
the large PC 71BM aggregates partially dissolved into PCE was correlated to the morphology optimization
smaller aggregates, which would increase the inter- according to measurements of GIWAXS and GISAXS.
faces of PTB7/PC 71BM in the active layer for promoted The results indicate that the halogen-free additive
J sc values of the PSC. In contrast, the GISAXS profile SH-na can form hydrogen bonds with both PTB7
for the active layer processed with the DIO additive and PC 71BM, resulting in substantially improved