A Simple Building Block with Noncovalently Conformational Locks towards Constructing Low-Cost and High-Performance Nonfused Ring Electron Acceptors

Nonfused ring electron acceptors (NFREAs) have attracted much attention due to their concise synthetic routes and low cost. However, developing high-performance NFREAs with simple structure remains a great challenge. In this work, a simple building block (POBT) with noncovalently conformational locks (NoCLs) was designed and synthesized. Single-crystal X-ray study indicated the presence of S⋯O NOCLs in POBT, thus enabling it to possess a coplanar conformation comparable to that of fused-ring CPT. Two novel NFREAs based on CPT and POBT were developed, namely TT-CPT and TT-POBT, respectively. Besides, TT-POBT possessed a smaller Stokes shift and a reduced reorganization energy compared with TT-CPT, indicating the introduction of S⋯O NoCLs can enhance the molecular rigidity even if simplifying the molecular structure. As a result, the TT-POBT-based PSC device afforded an impressive power conversion efficiency of 11.15%, much higher than that of TT-CPT counterpart (7.03%), mainly resulting from the tighter π-π stacking, improved and balanced charge transport, and more favorable film morphology. This work demonstrates the potential of the simple building block POBT with NoCLs towards constructing low-cost and high-performance NFREAs.