Improved Charge Transport and Absorption Coefficient in Indacenodithieno[3,2-b]thiophene-based Ladder-Type Polymer Leading to Highly Efficient Polymer Solar Cells

A novel ladder‐type donor (IDTT) is developed by substituting the two outward thiophenes of the IDT donor with two thieno[3,2‐b]thiophenes. The polymer derived from this donor possesses longer effective conjugation and better planarity, which improves electron delocalization along the polymer backbone and charge mobility. The polymer solar cell device using PIDTT‐DFBT shows a high power conversion efficiency of 7.03% with a large open‐circuit voltage of 0.95 V without using any additives or post‐solvent/thermal annealing processes.