Enhancing D/A Interactions via Porphyrin Isomerization to Improve Photovoltaic Performance.

The interactions between the electron donors and electron acceptors (D/A) play important roles for the performance of organic solar cells (OSCs). While the isomerization strategy is known to optimize molecular geometries and properties, the impacts of isomerization on the donors or acceptors in D/A interactions have not been extensively investigated. Here in, we innovatively investigated the impacts of donor isomerism on the D/A interactions by synthesizing two small molecule donors m-ph-ZnP and p-ph-ZnP by linking two functionalized porphyrins at the meta and para positions of phenyl groups, respectively. Compared with p-ph-ZnP, m-ph-ZnP displays reduced self-aggregation but enhanced interactions with PCBM. Consequently, a much higher power conversion efficiency (PCE) of 5.43 % is achieved for the m-ph-ZnP binary OSCs than the p-ph-ZnP devices with a PCE of 2.03 %. The enhanced performance of m-ph-ZnP-based device can be primarily attributed to the stronger intramolecular charge transfer (ICT), the enhanced D/A interactions, the improved charge transfer, and the suppressed charge recombination. Furthermore, the ternary devices based on m-ph-ZnP:Y6:PCBM achieve a PCE of 8.34 %. In short, this work elucidates the relationship among the chemical structure, D/A interactions and device performance, providing valuable guidelines for designing efficient OSCs materials.