Ternary copolymerization strategy is considered an effective method
to achieve high-performance photovoltaic conjugated polymers. Herein,
a donor–acceptor1–donor–acceptor2-type random
copolymer, named PBDTNS-TZ-BDD (T1), containing one electron-rich
unit alkylthionaphthyl-flanked benzo[1,2-b/4,5-b′] di-thiophene (BDTNS) as D and two electron-deficient
moieties benzo[1,2-c/4,5-c′]dithiophene-4,8-dione
(BDD) and fluorinated benzotriazole as A, was synthesized to investigate
the excitonic dynamic effect. Also, the D–A-type alternating
copolymer PBDTNS-BDD (P1) was also prepared for a clear comparison.
Although the UV–Vis spectra and energy levels of P1 and T1
are similar, the power conversion efficiencies (PCEs) of the related
devices are 11.50% (T1/ITIC) and 8.89% (P1/ITIC), respectively. The
reason for this is systematically investigated and analyzed by theoretical
calculation, photoluminescence, and pump-probe transient absorption
spectroscopy. The density functional theory (DFT) and time-dependent
density functional theory (TD-DFT) calculation results show that the
terpolymer T1 with a lower exciton binding energy and a longer lifetime
of spontaneous luminescence can synergistically increase the number
of excitons reaching the donor/acceptor interface. The results of
the pump-probe transient absorption spectroscopy show that the yield
of charge separation of T1/ITIC is higher than that of the P1/ITIC
blend film, and improved PCE could be achieved via copolymerization
strategies. Moreover, the fabrication of the T1-based device is also
simple without any additive or postprocessing. Therefore, it provides
a promising and innovative method to design high-performance terpolymer
materials.