Cyclization of Inner Linear Alkyl Chains in Fused-Ring Electron Acceptors Toward Efficient Organic Solar Cells

By changing the structures of the side chain on the backbone of the Y6 acceptor, many Y-series acceptors have been synthesized to investigate the relationships between structures and properties of the fused-ring electron acceptors (FREAs). However, not much attention has been paid to the effects of cycloalkane substituents on optoelectronic, morphological, and photovoltaic properties of the FREAs. Here, a brand-new FREA D12 is developed by incorporating cyclohexylmethyl functional groups into the pyrrole rings of the backbone of the Y6 acceptor, and a similar compound E12 with the linear n-heptane side chains is also synthesized for comparison. After the cyclization of the alkyl side-chain, the molecular orientation of D12 exhibits favorable face-on dominant, which endows D12 with higher charge mobility. Consequently, the organic solar cells (OSCs) with PM6 as donor and D12 as acceptor deliver the maximum power conversion efficiency of 17.3%, along with an excellent fill factor of 0.794, which is much higher than those of the PM6:E12-based OSCs. The results reveal that introducing an inner cyclized alkyl chain on the pyrrole motif is a simple and feasible strategy to regulate molecular orientation and improve photovoltaic properties, which might provide guidelines for developing high-performance electron acceptors.