PBDTTPD for plastic solar cells: Via Pd(PPh3)4-catalyzed direct (hetero)arylation polymerization

Polymeric photovoltaics have attracted considerable academic and industrial interest over the last few years because of their unique features. However, they still suffer from some drawbacks which have prevented so far massive industrial production. These drawbacks include high costs related to the preparation of active materials and high toxicity of organo-tin compounds usually involved in synthetic routes. In this context, we report the synthesis of one of the most promising polymers for bulk heterojunction (BHJ) solar cells, PBDTTPD (poly[(benzo[1,2-b:4,5-b′]dithiophene)-alt-(4H-thieno[3,4-c]pyrrole-4,6(5H)-dione)]), via Direct (Hetero)Arylation Polymerization (DHAP) in the presence, for the first time, of a low-cost Pd-catalyst [Pd(PPh3)4]. The outcome of the polymerization process is discussed in comparison with the synthesis of the same polymer via the Stille polycondensation. The photovoltaic performances of the polymer synthesized via DHAP are compared with those of the same polymer obtained via the Stille coupling and a commercially available PBDTTPD. The polymer synthesized by Pd(PPh3)4-catalyzed DHAP blended with PC71BM exhibits a power conversion efficiency up to 5.3%, higher than that of the Stille reference polymer, and comparable with that of the commercially available PBDTTPD, under the same processing conditions. These results confirm the potential of DHAP as a convenient alternative for the synthesis of D-A copolymers for plastic solar cells.