An efficient method to achieve a balanced open circuit voltage and short circuit current density in polymer solar cells

Abstract

Utilizing indacenodithiophene (D) and quinoxaline (A) building blocks, novel D–A–π–A type regular terpolymers of PIDT-DTQ-TT were designed with a conjugated π spacer of thieno[3,2-b]thiophene unit in the polymer backbone. In contrast to PIDT-DTQ with the thiophene unit as the spacer, PIDT-DTQ-TT displayed a much broader absorption with suitable HOMO energy levels and high charge carrier mobility. Also an enhanced J_sc of 12.43 mA cm⁻² and a V_oc of 0.83 V comparable to that of PIDT-DTQ-based devices were observed in PIDT-DTQ-TT-based solar cells, indicating that the balance between J_sc and V_oc in devices can be achieved when the spacer in the polymer backbone was altered individually in D–A–π–A type regular terpolymers. Finally, a maximum power conversion efficiency value of 6.63% was achieved without any post-treatment in solar cells. Our results here demonstrate that tuning the conjugated spacers in D–A–π–A type regular terpolymers individually could be an efficient method to balance the trade-off between J_sc and V_oc, leading to an enhanced photovoltaic performance in solar cells.