Developing a Fluorinated Benzothiadiazole‐Based Polymer Donor as Guest to Construct High‐Performance Ternary Solar Cells

Benzothiadiazole (BT) has shown promising applications in fullerene solar cells. However, few BT-based polymer donors exhibited a noticeable power conversion efficiency (PCE) for the fused-ring small molecular acceptor-based polymer solar cells (PSCs). Herein, we developed a D-A (D: donor, A: acceptor) polymer donor F-1 based on fluorinated BT (ffBT) as A unit and chlorinated benzo [1,2-b : 4,5-b'] dithiophene (BDT-2Cl) as D unit. Thanks to the strong electron-withdrawing of ffBT unit, F-1 not only exhibited low-lying energy levels to increase open circuit voltage, but also existence noncovalent S ⋅ ⋅ ⋅ F to enhance molecular planarity and crystallinity. After incorporated F-1 as guest materials on PM6 : L8-BO-based system to construct ternary device, the addition of F-1 can efficient promote the blend films exhibit excellent morphological compatibility, favorable phase separation, and molecular arrangement. As a result, the F-1 (5 %) : PM6 : L8-BO-based device obtained an impressive PCE up to 19.47 %, which is much higher than the counterparts as PCE is 18.35 % for PM6 : L8-BO-based binary device. This study not only provided a practical and promising strategy to develop high-performance polymer donors by utilizing the advantages of noncovalent conformational locks, but also suggested an efficient strategy to further improve device performance by constructing ternary solar cells for BT unit-based PSCs.