Figure 5. 2D-GIWAXS patterns of a) PBDB-T, b) BZO-4Cl, c)
PBDB-T: BZO-4Cl, d) PBDB-T: BZ4F-O-1 and e) PBDB-T: BZ4F-O-1: BZO-4Cl
films; f) In-plane (dashed) and out-of-plane (solid) GIWAXS curves of
the corresponding 2D patterns.
Conclusions
In conclusion, we employ a synergetic alkoxy side-chain and
chlorine-contained end group strategy for ultra-NBG heptacyclic SMAs.
And two A-DA’D-A type ultra-NBG acceptors, BZO-4F and BZO-4Cl are
designed and synthesized with theE gopt of 1.29 eV and 1.25 eV,
respectively. By blending with the polymer donor PBDB-T, the
BZO-4Cl-based device shows a moderate PCE of 12.48% with aJ SC of 26.86 mA cm-2, which is
slightly higher than that of the BZO-4F-based device. However, the
photovoltaic performance is limited by the lowV OC and FF. BZ4F-O-1 with a high LUMO level and a
complementary absorption is considered to be introduced into the PBDB-T:
BZO-4Cl system to construct ternary OSCs. As well investigated, the
ternary blend materials possess good miscibility. Besides, the
recombination process of the ternary device is suppressed and the charge
transport is significantly improved. Furthermore, the molecular π-π
stacking is also subtly controlled, leading to an optimal blend
morphology. Consequently, the PBDB-T: BZ4F-O-1: BZO-4Cl-based ternary
device achieves a high PCE of 15.51% with the simultaneously increasedV OC (0.77 V), J SC (27.85
mA cm-2) and FF (0.71). This work highlights a
molecular strategy of altering the oxygen position along the side chains
and chlorine-substitution for ultra-NBG acceptor, which is a potential
alternative in semi-transparent OSCs.
Experimental
Synthesis of BZO-4F andBZO-4Cl: Under argon,
compound 9 (0.14 g,0.12 mmol) and
2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (0.11
g, 0.48 mmol) were dissolved in chloroform (30 mL). Pyridine (1.5 mL)
was added. After stirring at 65 oC overnight, the
mixture was cooled to room temperature, the solution was concentrated
under reduced pressure, and poured into methanol and filtered. The
residue was purified in a silica gel column using petroleum
ether/dichloromethane (1:1, v/v) as the eluent. BZO-4F was obtained as a
dark blue solid (135 mg, 70% yield). BZO-4Cl was synthesized by the
same method of BZO-4F.
Device fabrication: The optimized photovoltaic devices were
fabricated with a conventional structure of Glass/ITO/PEDOT: PSS/
PBDB-T: acceptor/PDINN/Ag. Pre-patterned ITO coated glass substrates
(Advanced Election Technology Co., Ltd) were washed with deionized water
and isopropyl alcohol in an ultrasonic bath for 15 minutes. After
blow-drying by high-purity nitrogen, all ITO substrates are cleaned in
the ultraviolet ozone cleaning system for 20 minutes. Subsequently, a
thin layer of PEDOT: PSS (Xi’an Polymer Light Technology Corp 4083) was
deposited through spin-coating on pre-cleaned ITO-coated glass at 4500
rpm for 30 s and dried subsequently at 150°C for 15 minutes in
atmospheric air. Then the photovoltaic layers were spin-coated in a
glovebox from a solution of PBDB-T: acceptors (14.5mg/mL with 0.1vol%
CN with the PBDB-T: acceptors weight ratios of 1:1.2, PBDB-T: BZ4F-O-1:
BZO-4Cl = 1: 0.6: 0.6) in CF. The optimal active layers were fabricated
by spin-coating at about 3000 rpm for the 30s. Then the blend films were
treated with thermal annealing at 100 oC for 10 min.
After cooling to room temperature, a PDINN layer via a solution
concentration of 1 mg/mL was deposited at the top of the active layer at
a rate of 3000 rpm for 30 s. Finally, the top Ag electrode of 100 nm
thickness was thermally evaporated through a mask onto the cathode
buffer layer under a vacuum of 1.5×10-4 Pa.
Supporting Information
The supporting information for this article is available on the WWW
under https://doi.org/10.1002/cjoc.2021xxxxx.
Acknowledgement
This work was supported by National Natural Science Foundation of China
(52125306, 22005347).
Author contributions
Yingping Zou and Qingya Wei conceived the idea and designed the
acceptors. Qingya Wei synthesized the acceptor materials and tested the
molecular optoelectronic properties. Songting Liang fabricated the
organic solar cells and characterized the photovoltaic parameters.
Qingya Wei and Songting Liang tested the AFM and TEM. BeiBei Qiu helped
the theoretical calculations. Xinhui Lu and Yuang Fu supported the
GIWAXS. Qingya Wei wrote the original draft, and all the authors
including Jun Yuan, Wei Liu and Xiang Xu contributed to the data
analysis and manuscript revision. Yingping Zou directed this project.
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