Subtly Modulating Bay Sites of Perylene Diimide Cathode Interface Layer for High‐Performance and High‐Stability Non‐Fullerene Organic Solar Cells

Abstract Cathode interface layers (CILs) are crucial for optimizing the power conversion efficiency (PCE) and stability of organic solar cells (OSCs). Two small molecule CILs, PDINN‐TS and PDINN‐BS are developed, by modifying the bay sites of perylene diimide (PDI) with thieno [3,2‐b] thiophene and 2,2′‐bithiophene, separately. Due to better electron‐donating capacity and longer conjugate length of the 2,2′‐bithiophene, PDINN‐BS exhibits a stronger self‐doping effect and superior interface compatibility compared to PDINN‐TS. Consequently, in PM6: Y6 OSCs, PDINN‐BS achieved an elevated PCE of 16.95%, surpassing PDINN‐TS of 16.66%. Meanwhile, PDINN‐BS exhibits excellent universality. When employing PM6: BTP‐eC9 and PM6:L8‐BO systems, PDINN‐BS‐based device yielded PCE of 18.02% and 18.95%, outperforming PDINN‐TS of 17.51% and 18.38%, respectively. Furthermore, stability tests revealed that after being stored in the glovebox for 1500 h, PDINN‐BS retained 90% of its pristine PCE, compared to 86% for PDINN‐TS. PDINN‐BS showed longer 80% PCE decay (T ₈₀ ) of 150 h in air, 200 h at 70 °C heating in N ₂ , and 500 h under 1 sun immersion, surpassing PDINN‐TS with 120, 130, and 380 h, respectively. This demonstrates that PDINN‐BS displayed superior stability under a complicated environment. Consequently, this study provides significative guidance for the exploitation of high‐performance and high‐stability OSCs.