Fluorinated D1(0.5)–A–D2(0.5)–A model terpolymer: ultrafast charge separation kinetics and electron transfer at the fluorinated D/A interface for power conversion†
A model fluorinated semiconductivity terpolymer, PBTA-PS-F (D1–A–D2–A), was synthesized and used in polymer solar cells (PSCs). This terpolymer possessed optimal energy levels (HOMO and LUMO, −5.48/−3.53 eV) and a complementary absorption region with small molecule acceptor ITIC. Two-dimensional grazing incidence X-ray (2D-GIXD) studies indicated that PBTA-PS-F exhibits strong lamellar stacking and preferable face-on orientation in the pristine film and the film blended with ITIC. A large ground to excited state dipole moment Δμge of 1.84 D was calculated for PBTA-PS-F, which was larger than that of its counterpart copolymer PBTA-PS (0.27 D). Furthermore, ultrafast electron transfer at the fluorinated terpolymer D/A interface was found from the ground state bleach signature (GSB) and excited state absorption signature (ESA) signals. Therefore, a high power conversion efficiency of 13.48% was achieved for the optimized PBTA-PS-F:ITIC device. As a result, employing structurally similar donor moieties as modulators to construct D1–A–D2–A model terpolymers can be used to improve the performance of polymer solar cells.