Non-fused ring electron acceptors for high-performance and low-cost organic solar cells: Structure-function, stability and synthesis complexity analysis

In recent years, the development of non-fullerene acceptors (NFAs) has led to rapid advances in organic solar cells (OSCs), resulting in power conversion efficiency (PCE) exceeding 19%. However, the complex molecular architectures of fused ring electron acceptors require increasing steps of synthesis and purification, restricting their mass synthesis and hindering the commercialization of OSCs. Non-fused ring electron acceptors (NFREAs), on the other hand, offer several advantages, including facile synthesis, simple chemical modifications, and easy tunability in the optical band gap, frontier molecular orbitals and absorption spectrum. In the last five years, various types of NFREAs have been designed and synthesized, necessitating a timely review article. In this review, we analyze the molecular structure design and structure-property relationship of NFREAs, discuss their stability and figure-of-merit (FOM) values compared to traditional fused ring electron acceptors, and explore the challenges and prospects of NFREAs for achieving high-performance device and low-cost manufacturing concurrently.