Interplay Between π‐Conjugated Polymer Donors and Acceptors Determines Crystalline Order of Their Blends and Photovoltaic Performance

Abstract

AbstractCrystallinity of π‐conjugated polymer donors as well as acceptors is a crucial factor for boosting the performance of organic photovoltaic (OPV) cells. However, in the state‐of‐the‐art OPVs based on nonfullerene acceptors (NFAs), π‐conjugated polymers with low crystallinity are typically used and provide high efficiencies. Here, π‐conjugated polymers, named PTzBT and PTzBTE based on thiazolothiazole (TzTz), having similar crystallinity but different aggregation properties are blended with a number of acceptor materials such as PC71BM, IT‐4F, Y6, and Y12 having different aggregation property. Interestingly, whereas PTzBTE with higher aggregation properties forms crystalline structures in the blends regardless of the acceptor material, PTzBT with lower aggregation properties exhibits crystalline structures only when blended with acceptors having higher aggregation properties. Notably, the crystalline order of the materials in the blend films is correlated closely with the OPV performance. This study proposes that the interplay between the polymer donor and acceptor will play a crucial role in determining the crystalline order in the bulk heterojunction systems and thereby high photovoltaic performance.