Effect of the Selective Halogenation of Small Molecule Acceptors on the Blend Morphology and Voltage Loss of High-Performance Solar Cells

Abstract

Herein, the impacts of the selective halogenation at two different positions ofdicyanomethylene-3-indanone (IC) end groups and inner side chains of smallmolecular acceptors (SMAs) on the PD:SMA interfacial interactions, blendmorphology, and resulting photovoltaic properties are described. In this study,four different SMAs (A1, A2, A3, and A4) with the same molecular backbone,but with different degrees of halogenation, are synthesized. The IC end groupson the backbones of the A1 and A3, and A2 and A4 SMAs are chlorinatedand fluorinated, respectively; in addition, 6-phenoxyhexyl inner side chainsof the A3 and A4 are chlorinated. The SMAs are paired with a chlorinatedPBDT-Cl PD to construct organic solar cells (OSCs). The PBDT-Cl:A4-basedOSC exhibits the highest power conversion efficiency of 17.2%, outperformingthe PBDT-Cl:A1-(13.3%), PBDT-Cl:A2-(15.6%), and PBDT-Cl:A3-based OSC(16.5%). The Cl atoms on the side chains in the A3 and A4 SMAs enhance themolecular/energetic interactions at the PD:SMA interfaces and improve theblend morphology in terms of domain purity and spacing. These effects leadto the improved fill factors and reduced voltage loss of the PBDT-Cl:A3- andPBDT-Cl:A4-based OSCs. This study demonstrates the importance ofappropriate halogenation of SMAs in optimizing the blend morphology,reducing voltage loss, and improving OSC performance.