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

Utilizing indacenodithiophene (D) and quinoxaline (A) building blocks, novel D-A-pi-A type regular terpolymers of PIDT-DTQ-TT were designed with a conjugated pi 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-pi-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-pi-A type regular terpolymers individually could be an efficient method to balance the trade-off between J(s,) and V-oc, leading to an enhanced photovoltaic performance in solar cells.