Core-Functionalized 1,4-Naphthoquinone-Based Polymer Donors for Efficient and Stable Quasi-Planar Heterojunction Organic Solar Cells

Although organic solar cells (OSCs) have achieved major breakthroughs in device efficiency, the development of high-performance polymer donors still lags behind that of acceptors. Herein, we engineered a novel 1,4-naphthoquinone-based building block, naphtho[2,1-b:3,4-b′]dithiophene-4,7-dione (NDTD), by embedding a 1,4-naphthoquinone skeleton into a rigid fused-ring architecture. Based on this scaffold, a series of polymer donors with methyl, hydrogen, and fluorine substituents were synthesized to systematically regulate their optoelectronic properties and photovoltaic potential. When paired with L8-BO in quasi-planar heterojunction (Q-PHJ) devices, the NDTD-Me-based OSCs achieved a champion efficiency of 16.21% and exceptional operational stability, exhibiting T80 lifetimes exceeding 1800 h under storage and continuous illumination, and nearly 1730 h under thermal stress at 65 °C, outperforming both the H- and F-substituted counterparts. Mechanistic investigations further revealed that the superior molecular packing and optimized active-layer miscibility of NDTD-Me/L8-BO contributed to enhanced exciton dissociation, suppressed charge recombination, balanced carrier transport, and reduced energy loss. These findings validate NDTD as a robust electron-deficient platform and highlight rational quinone functionalization as a powerful strategy for concurrently achieving high efficiency and stability in OSCs.