Nonacyclic carbazole-based non-fullerene acceptors enable over 12% efficiency with enhanced stability for organic solar cells

Abstract

In this work, a nonacyclic carbazole-cored electron-rich central building block called CZTT and its derivative non-fullerene acceptors (CZTT-IC and CZTT-4F) are designed and synthesized. CZTT-4F with fluorinated acceptor end groups shows significantly down-shifted energy levels and a narrower bandgap as well as a smaller dipole moment in the ground state in comparison to the counterpart CZTT-IC. In the blend films, blends of both the fluorinated donor and acceptor (PM6:CZTT-4F) reveal relatively lower miscibility resulting in a better donor/acceptor interpenetrating network with higher domain purity for efficient charge transport. Organic solar cells (OSCs) based on the PM6:CZTT-4F blend exhibited a highest power conversion efficiency (PCE) of 12.07% with enhanced thermal and light soaking stability. To the best of our knowledge, this performance is among the best for carbazole-based OSCs in the literature. The results reveal that the nonacyclic CZTT core is a promising building block for constructing efficient non-fullerene acceptors. More importantly, the relatively lower miscibility within the fluorinated CZTT-based blend film is demonstrated to greatly improve the stability of OSCs.