In this study, we synthesized four new A–DA′D–A
acceptors (where A and D represent acceptor and donor chemical units)
incorporating perylene diimide units (A′) as their core structures
and presenting various modes of halogenation and substitution of the
functional groups at their end groups (A). In these acceptors, by
fusing dithiophenepyrrole (DTP) moieties (D) to the helical perylene
diimide dimer (hPDI) to form fused-hPDI (FhPDI) cores, we could increase
the D/A′ oscillator strength in the cores and, thus, the intensity
of intramolecular charge transfer (ICT), thereby enhancing the intensity
of the absorption bands. With four different end group unitsIC2F,
IC2Cl, IO2F, and IO2Cltested, each of these acceptor molecules
exhibited different optical characteristics. Among all of these systems,
the organic photovoltaic device incorporating the polymer PCE10 blended
with the acceptor FhPDI-IC2F (1:1.1 wt %) had the highest power conversion
efficiency (PCE) of 9.0%; the optimal PCEs of PCE10:FhPDI-IO2F, PCE10:FhPDI-IO2Cl,
and PCE10:FhPDI-IC2Cl (1:1.1 wt %) devices were 5.2, 4.7, and 7.7%,
respectively. The relatively high PCE of the PCE10:FhPDI-IC2F device
resulted primarily from the higher absorption coefficients of the
FhPDI-IC2F acceptor, lower energy loss, and more efficient charge
transfer; the FhPDI-IC2F system experienced a lower degree of geminate
recombinationas a result of improved delocalization of π-electrons
along the acceptor unitrelative to that of the other three
acceptors systems. Thus, altering the end groups of multichromophoric
PDI units can increase the PCEs of devices incorporating PDI-derived
materials and might also be a new pathway for the creation of other
valuable fused-ring derivatives.
A new terpolymer acceptor is presented, comprising various ratios of the same dithienothienopyrrolobenzothiadiazole (BTP) core with different side chains—alkoxy side chains (BTPO‐IC) and alkyl side chains (BTP‐IC)—and thiophene units, for use in all‐polymer organic photovoltaics. Devices incorporating binary blends of this terpolymer and the polymer PM6 as the active layer displayed open‐circuit voltages (VOC) that increase linearly upon increasing the molar ratio of BTPO‐IC. For example, the optimized device incorporating PM6:PY‐0.2OBO (i.e., with 20 mol% of BTPO‐IC) (1:1.2 wt.%) blend, with the smallest domain sizes but largest coherence length and combined face‐on and edge‐on orientation fractions among all blends, have a champion power conversion efficiency (PCE) of 16.7% (VOC = 0.97 V; JSC = 25.2 mA cm−2; FF = 0.68), whereas the device containing a similar blend ratio of the PM6:PY‐OD:PY‐OBO ternary blend (1:0.96:0.24 wt.%) displayed a PCE of 8.6% (VOC = 0.969 V; JSC = 18.7 mA cm−2; FF = 0.48). The device with PM6:PY‐0.2OBO displays better thermal stability than the devices with PM6: PY‐OD or PY‐OBO. Thus, employing terpolymer acceptors with differently functionalized side‐chain units can be an effective approach for simultaneously optimizing the aggregation domain and enhancing the PCEs and thermal stabilities of all‐polymer devices.
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