Photovoltaic donor-acceptor conjugated polymers with minimally substituted acceptor moieties

A novel family of conjugated donor-acceptor (D-A) copolymers designed with comparatively small methyl substituted acceptor units was synthesized for use as donor phase materials in bulk heterojunction (BHJ) organic photovoltaic (OPV) applications. These polymers make use of common acceptor moieties thieno [3,4-c] pyrrole-4,6-dione (TPD), diketopyrrolopyrrole (DPP), and isoindigo (iI) with methyl side chains to provide sterically unhindered sites for enhanced interactions with a molecular acceptor (MA), either PC71BM or ITIC in this study. The resulting polymers P(T4-TPD-M), P(T4-DPP-M), and P(T4-iI-M) were utilized in BHJ OPV devices where the highest performing D-A polymer, P(T4-TPD-M), obtained a maximum PCE of 7.5% with PC71BM and 4.0% with ITIC. These results indicate that minimally-sized methyl side chain derivatives of TPD, DPP, and iI can be useful acceptor moieties in D-A polymer systems, and the impact of sterics on the acceptor moiety can be elucidated in future studies through modification of the methyl side chain to bulkier aliphatic substituents.