Facile Direct C‐H Arylation Polymerization of Conjugated Polymer, PDCBT, for Organic Solar Cells

Abstract Direct arylation polymerization (DArP) is a synthetic method for conjugated polymers; in DArP, organometallic functionalization steps are omitted and there are no toxic byproducts. As a result, it is considered a more sustainable alternative compared to conventional methods such as Stille polymerization. To explore the possibility of DArP‐based polymers as donor materials in organic solar cells (OSCs), a series of conjugated polymers based on the structure of PDCBT (poly[2,2''''‐bis[[(2‐butyloctyl)oxy]carbonyl][2,2':5',2'':5'',2'''‐quaterthiophene]‐5,5'''‐diyl]) are synthesized using DArP and Stille polymerization. By controlling the monomer concentration and reaction time in DArP, DArP‐5 with the highest Mn (21.9 kDa) can be obtained and its optoelectronic properties, electrochemical properties, and microscopic molecular ordering are comparable to those of Stille‐based PDCBT (Stille‐P). Analysis of the polymer structure indicates no structural defects such as crosslinking from undesired β‐coupling reactions in DArP‐5. Upon blending with the PC71BM acceptor molecule, an increase in the crystallite size of DArP‐5 is also observed. In OSC devices with a polymer:PC71BM bulk‐heterojunction photoactive layer, DArP‐5 demonstrates a comparable power conversion efficiency of 5.8% with that of Stille‐P (5.5%). These results prove that DArP is suitable for synthesizing PDCBT, and DArP‐based PDCBT can be used in OSCs as an alternative of Stille‐based one.