Synergistically Modulating the Bay and Amid Sites of a Perylene Diimide Cathode Interface Layer for High-Efficiency and High-Stability Organic Solar Cells

Simultaneously enhancing the power conversion efficiency (PCE) and stability of organic solar cells (OSCs) is a pivotal issue to advance their commercial feasibility. The frequently used cathode interface layer (CIL) based on perylene diimide (PDI) derivatives usually causes some problems, such as unmatched surface energies (γs) with an active layer, strong aggregation, and poor stability. Herein, the bay and amide position synergistically benzoyl hydrazide-functionalized PDI-based CILs, namely PDI-4NOPN and PDINN-NOPN, have been designed and synthesized. Compared with PDI-4NOPN with a PCE of 14.85%, the PDINN-NOPN-applied OSCs display a higher PCE of 17.37% (PM6: BTP-eC9) with more excellent device stabilities under diverse conditions. Furthermore, PDINN-NOPN demonstrates an impressive level of insensitivity to thickness, maintaining a PCE over 92% even when the thickness is up to 19 nm, which is attributed to the powerful self-doping effect, superior work function (Wf) modulating capability, excellent morphology and proper crystallinity, and the low impedance of PDINN-NOPN. The inferior performance observed in PDI-4NOPN is ascribed to the decrease of electron cloud distribution resulting from an excess of carbonyl groups. Carbonyl groups intensify the electron-withdrawing characteristic of the benzoyl groups, consequently impeding the charge transfer process. Thus, collaboratively optimizing the bay and amid sites of PDI represents a practical approach for achieving high-efficiency, high-stability, and thickness-insensitive OSCs.