Figure 4 (a) Tapping-mode AFM height images (2 μm × 2 μm) (insets are phase images of 1 μm × 1 μm size), (b) TEM images, and (c) 2D-GIWAXS patterns of J52:NoCA-17, J52:NoCA-18, and J52:NoCA-19 blend films.
Morphology investigation
The surface and bulk morphologies of blend films were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). As shown in Figure 4a, the J52:NoCA-19 blend film exhibits a uniform surface with a higher root-mean-square (R q) surface roughness of 1.57 nm compared to the J52:NoCA-17 (1.09 nm) and J52:NoCA-18 (1.43 nm) blend films. Furthermore, Figure 4b shows that the J52:NoCA-19 blend film exhibits smaller domain sizes and nano-scale phase separation. To provide further insight into the molecular packing in the blend films, 2D-GIWAXS was employed (Figures 4c and S5). The NoCA-17-based blend film demonstrates overlapping lamellar packing diffraction peaks with the polymer J52. Interestingly, the lamellar packing diffraction peaks of the acceptors in the NoCA-18 and NoCA-19-based blend films remain clear, indicating that the order packings of NoCA-18 and NoCA-19 were not vulnerable to be disturbed when blending with J52. This features in film morphology are beneficial for charge transport and thus device performance.
Conclusions
In conclusion, the asymmetric end-group engineering was employed to construct a new NFREA, namely NoCA-19 containing two distinct end-groups, IC-2Cl and NC-2F. Together with two symmetrical NFREAs (NoCA-17 and NoCA-18), experimental and theoretical studies were systematically carried out, showing that asymmetric acceptor NoCA-19 possesses broad light absorption range, more coplanarπ -conjugated backbone, and appropriate crystallinity. The NoCA-19-based device delivered a champion PCE of 12.26%, mainly due to the best and most balanced carrier mobility, least charge recombination, shortest charge extraction time, and most favorable morphology among the three blend systems. This work sheds light on the potential of asymmetric end-group engineering in designing low-cost and high-performance NFREAs.
Supporting Information
The supporting information for this article is available on the WWW under https://doi.org/10.1002/cjoc.2023xxxxx.
Acknowledgement
B. Liu and C. Li contributed equally to this work. The authors acknowledge the financial support from the NSFC (2197505, U2001222, 52103352, 52120105006, and 51925306), National Key R&D Program of China (2018FYA 0305800), Key Research Program of Chinese Academy of Sciences (XDPB08-2), the Youth Innovation Promotion Association of Chinese Academy of Sciences (2022165), and the Fundamental Research Funds for the Central Universities. DFT results described in this article were obtained from the National Supercomputing Centre in Shenzhen (Shenzhen Cloud Computing Centre).
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