Enhanced Photovoltaic Performance by Synergistic Effect of Chlorination and Selenophene pi-Bridge

In the rapid innovation of organic solar cells, polymer donor plays a significant role in achieving high power conversion efficiencies (PCEs). The strong intermolecular interactions and deep highest occupied molecular orbitals (HOMOs) of donor polymers will facilitate the favorable phase separation and high open-circuit voltage (V-oc), resulting in the dramatic improvement of device performance. Herein, combined chlorination of 4,8-bis(thiophene-2-yl)-benzo[1,2-b:4,5-b']-dithiophene (T-BDT) and selenophene pi-bridges, a new polymer donor, named PBBSe-Cl, is designed and synthesized. Compared to its parent polymer without chlorine substitution and pi-bridge (named PBB), PBBSe-Cl exhibits much stronger absorption, better molecular planarity, and improved molecular aggregations. Moreover, PBBSe-Cl shows favorable phase separation and bicontinuous interpenetrating network when blending with acceptor Y6. As a result, the inverted device based on PBBSe-Cl achieves a decent PCE of 14.44%, with synchronously improved short-circuit current density (J(sc)) of 24.07 mA cm(-2) and fill factor (FF) of 73.16%. However, its parent polymers PBB and PBBSe-H only present a relatively low device performance. In addition, a very low energy loss (E-loss) of 0.51 eV is realized for PBBSe-Cl-based devices. This investigation proves that introducing chlorine atoms on the conjugated side chains and selenophene it-bridges will stepwise increase the polymer solar cell efficiency due to the simultaneous enhancement of device current density and fill factor. The proper usage of chlorination and selenophene pi-bridge is a facile and efficient strategy for high-performance solar conversion materials.