Isomerization of Benzothiadiazole Yields A Promising Polymer Donor and Organic Solar Cells with Efficiency of 19.0.

The exploration of high-performance and low-cost wide-bandgap polymer donors remains critical to achieve high-efficiency non-fullerene organic solar cells (OSCs) beyond current thresholds. Herein, the 1,2,3-benzothiadiazole (iBT), which is an isomer of 2,1,3-benzothiadiazole (BT), is used to design wide-bandgap polymer donor PiBT. The PiBT-based solar cells reach efficiency of 19.0%, which is one of the highest efficiencies in binary OSCs. Systemic studies show that isomerization of 2,1,3-benzothiadiazole (BT) to 1,2,3-benzothiadiazole (iBT) can finely regulate the polymers' photoelectric properties including (i) increase the extinction coefficient and photon harvest, (ii) down-shift the highest occupied molecular orbital (HOMO) energy levels, (iii) improve the coplanarity of polymer backbones, (vi) offer good thermodynamic miscibility with acceptors. Consequently, the PiBT:Y6 BHJ device simultaneously reaches advantageous nanoscale morphology, efficient exciton generation and dissociation, fast charge transportation, and suppressed charge recombination, leading to larger V OC of 0.87 V, higher J SC of 28.2 mA·cm -2 , greater FF of 77.3%, and thus higher efficiency of 19.0%, while the analogue PBT-based OSCs reach efficiency of only 12.9%. Moreover, the key intermediate 1,2,3-benzothiadiazole (iBT) can be easily afforded from industry chemicals via two-step procedure. Overall, this contribution highlights that 1,2,3-benzothiadiazole (iBT) is a promising motif for designing high-performance polymer donors. This article is protected by copyright. All rights reserved.