A facile strategy to enhance absorption coefficient and photovoltaic performance of two-dimensional benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-c]pyrrole-4,6-dione polymers via subtle chemical structure variations

• The incorporation of alkyl-thiophene spacers were beneficial for 2D BDT-RT and TPD combination polymer at absorption coefficient.
• The polymer with spacers exhibited better PSC performance up to 6.08%.
• The result was distinct from alkyl-thiophene spacer effect on other BDT-TPD structured polymers reported.

Two novel donor–acceptor (D–A) type conjugated polymers using thiophene and hexyl-thiophene spacers between two-dimensional alkyl-thiophene substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-RT) and alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) units are synthesized and characterized. The effects of incorporation of alkyl-thiophene spacers in the polymer backbone on the optical, electrochemical, charge transport and photovoltaic properties are studied. The bulk-heterojunction (BHJ) polymer solar cells (PSCs) based on the polymer with hexyl-thiophene spacers show much better performance (with power conversion efficiency up to 6.08%) than that of polymer without spacers, which is very distinct from alkyl-thiophene spacer effect of other BDT-TPD structured polymers reported previously. The experimental results and theoretical calculations show that a subtle tuning of chemical structure can significantly influence the absorption coefficient by inserting alkyl-thiophene spacers in the polymer backbone. This provides an important route for designing new materials to obtain higher current density (Jsc) and fill factors (FF).

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