Fluorine‐Substituted π‐Bridge through a Simple Method for Efficient Polymer Donor

Abstract

Herein, a novel fluorinated conjugated polymer, PM7‐F, as the donor material for polymer solar cells (PSCs) is developed. In contrast to previously reported synthetic methods for 3‐fluorothiophene, a crucial intermediate, 3‐fluoro‐2‐iodothiophene, is utilized, to shorten the synthetic route and ensure lower synthetic costs via a simple approach. The effects of fluorine substituent on the π‐bridge unit are systematically investigated. PM7‐F displays great planarity and a nearly linear backbone via its strong intramolecular noncovalent conformation locks. Due to the strong noncovalent contacts of F–S, F–π, and F–Cl, as well as the large dipole moment of carbon–fluorine (C–F), the fluorinated polymer PM7‐F possesses redshifted absorption, a much deeper highest occupied molecular orbital level (−5.65 eV), better crystallinity, enhanced nanoscale morphology, efficient charge transport properties, and reduced recombination behaviors than its nonfluorine counterpart. As a result, the PM7‐F:ITIC‐based PSCs exhibit a remarkable power conversion efficiency of 13.46% with a open‐circuit voltage of 0.94 V, a short‐circuit current of 20.79 mA cm−2, and an fill factor of 68.87%. Herein, it is indicated that fluorination π‐bridge provided a feasible approach to obtain low‐cost and high‐efficiency polymer donors.