Synthesis and photovoltaic properties of 2D-conjugated polymers with alkylsilyl-substituted thieno[3,2-b]thiophene conjugated side chains

We designed and synthesized two new donor-acceptor (D-A) copolymers J46 and J47 through replacing thiophene conjugated side chains by thieno[3,2-b]thiophene (TT) in the benzo[1,2-b:4,5-b’]dithiophene (BDT) units copolymerized with fluorobenzotriazole (FBTA). J46 possesses alkyl substituent on the TT conjugated side chains and J47 with alkylsilyl substituent on the TT side chains. Power conversion efficiency (PCE) of the polymer solar cells (PSCs) based on J47 as donor and an n-type organic semiconductor (n-OS) ITIC as acceptor with thermal annealing at 150 °C for 2 min and with DIO additive treatment reached 9.0%, while the PCE of the J46-based PSCs was only 2.33%. The results indicate that the size and nature of the conjugated side chains in the J-series BDT-alt-FBTA copolymers influence the physicochemical and photovoltaic properties of the 2D-conjugated polymers significantly, and the side chain engineering could play an important role in improving the photovoltaic performance of the 2D-conjugated polymer donor materials.