Conjugated Mesopolymer Achieving 15% Efficiency Single‐Junction Organic Solar Cells

The high‐performance organic solar cells (OSCs) tend to choose the polymers with high molecular weight as donors, which easily produce good crystallinity to facilitate intermolecular charge transfer. However, these polymers usually accompanied by the low solubility and synthetic difficulty, increasing batch‐to‐batch variations. The proposal of conjugated mesopolymers (molar mass (M (n)) in 1–10 kDa) can overcome these problems. Herein, a new mesopolymer, MePBDFCl( H ) as donor material is designed and synthesized, and firstly applied in OSCs. As a comparison, other lower molecular weight mesopolymer of MePBDFCl( L ) and higher molecular weight polymer of PBDFCl with same structure are also prepared and investigated. Because of its appropriate phase separation and miscibility in the blend film, the MePBDFCl( H ) exhibits the highest power conversion efficiency (PCE) of 15.06% among the three materials. Meanwhile, the champion PCE is a new record for benzo[1,2‐b:4,5‐b′]difuran‐based photovoltaic materials. Importantly, comparing to the pronounced PCE decrease of polymer PBDFCl by about 12%, a slightly PCE difference for mespolymer MePBDFCl( L ) is only less than 5%, reducing the batch‐to‐batch variation. This work not only suggests that the benzo[1,2‐b:4,5‐b′]difuran unit is a promising electron‐donating core but also shows that the mesopolymers have great potentials to produce the low‐differentiated and high‐performance organic photovoltaic materials.