Enhanced photovoltaic performance of donor polymers effected by asymmetric π-bridges

Abstract

Precise control of π-bridge segments is of vital importance in the construction of conjugated polymers, which are extensively used in organic solar cells. In this work, three conjugated polymers, P1, P2 and P3, with different asymmetric π-bridges in the main chains, were produced for the first time through a simple one-pot chemical synthesis method. Compared to their symmetric control counterparts (P4 and P5), asymmetric structures show larger dipole moments, strong intermolecular interactions, and regulated energy levels. By blending with the non-fullerene acceptor Y6, the three conjugated polymers based on asymmetric π-bridges exhibited better photovoltaic properties. In particular, the power conversion efficiency (PCE) and the fill factor (FF) of a P2-based device could reach 16.22% and 74.81%, respectively. In contrast, an inferior PCE of 1.32% is obtained for a symmetric polymer P5-based device. The results reveal that the asymmetric π-bridge strategy is promising for tailoring the backbone configuration of conjugated polymers and improving the photovoltaic properties of organic solar cells.