Mechanistic Studies of Effect of Dispersity on the Photovoltaic Performance of PTB7 Polymer Solar Cells

Bulk heterojunction (BHJ) polymer solar cells (PSCs) are a popular research subject currently pursued by many groups around the world. The state-of-the-art PSCs are composed of a polymer donor and a fullerene acceptor as the active layer, and their overall photovoltaic performance is dependent on many factors, such as the electrical and optical properties of donor polymers, device architectures, and interfacial layers used. Among them, the nature of donor polymer is without doubt one of the determining factors in performance of PSCs. In this work, we report for the first time the study of the influence of polymer dispersity (D) on the performance of PSCs composed of PTB7 and PC71BM as the active layer materials. It was found that polymers exhibiting large D contained structural defects that played the role of energy transfer and charge trapping/recombination centers. The power conversion efficiency of PTB7 devices decreased from 7.59% to 2.55% with increased D. The results highlighted the importance of controlling D of donor polymers for PSCs.