Fused benzotriazole as the A′ unit to construct A–D–A′–D–A-type non-fused ring electron acceptors for efficient organic solar cells

A–D–A′–D–A-type non-fused ring electron acceptors (NFREAs) are a kind of important photovoltaic materials, and thus developing high-performance electron-deficient central units is crucial for further enhancing their photovoltaic properties.