Delicate chemical structure regulation of nonfullerene acceptor for efficient and large thickness organic solar cells

Inspired by the success of CH-series acceptors, a small-molecular acceptor, CH-Tz was reported by adopting a new conjugation-extended electron-deficient unit ([1,2,5]thiadiazolo[3,4-b]pyrazine) on the central core. Owing to the enhanced inter-/intra-molecular interactions, CH-Tz exhibited near-infrared absorption and an effective three-dimensional molecular packing network in its single crystal. When blended with polymer donor PM6, the binary device achieved a high power conversion efficiency (PCE) of 18.54%, with a notable short-circuit current density (J_sc) of 27.54 mA cm⁻² and an excellent fill factor (FF) over 80%, which can be partly ascribed to the balanced charge transport properties in the blend film. After employing D18-Cl as the third component, an enhanced PCE of 18.85% was achieved due to a more obvious fiber network. Impressively, the CH-Tz-based OSC devices show excellent thermal stability and thickness insensitivity. Record-breaking J_sc of 28.92 mA cm⁻² was reached for PM6:D18-Cl:CH-Tz ternary device with a thickness of 560 nm. Besides, CH-Tz shows potential in fabricating multicomponent high-performance organic solar cells, where over 19% efficiency could be realized in the quaternary device. Our work advances the strong influence of electron-deficient central units on molecular photovoltaic properties and guides the design of acceptors for stable and large-thickness organic solar cells.