Noncovalent Modulation of DPB:PFN-Br Cathode Interlayers Enables Stable and High-Efficiency Organic Solar Cells

Engineering of the cathode interlayer is critical to achieving high efficiency and stability in organic solar cells; however, the alcohol-soluble polymer poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] bromide (PFN-Br) remains constrained by local disorder and insufficient electron selectivity. Upon incorporating 3-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzoic acid (DPB) into PFN-Br, quantum-chemical calculations and reduced-density-gradient/noncovalent-interaction analyses suggest cooperative noncovalent interactions (π–π stacking and hydrogen-bonding/polar interactions) that promote a more compact and polarized interlayer, thereby improving charge-selective electron extraction, interfacial transport, and charge collection at the cathode interface while suppressing interfacial losses, rather than influencing exciton dissociation in the bulk active layer. Consistent with these microscopic indications, the conductivity increases from 1.58 × 10–4 to 2.24 × 10–4 S cm–1 and the electron mobility rises from 1.25 × 10–4 to 2.45 × 10–4 cm2 V–1 s–1; the carrier extraction time shortens to 16.7 μs, while the carrier lifetime extends to 5.3 ms. Under the PM6:Y6 active layer, an optimal DPB content of 0.25 mg mL–1 yields a champion power-conversion efficiency of 16.52%; the short-wavelength external quantum efficiency is enhanced, device-to-device uniformity improves, and 90% of the initial efficiency is retained after 28 days in nitrogen. These results indicate that interlayer densification and polarization in DPB-modified PFN-Br provide a solution-process-compatible route to concurrently increase the short-circuit current density and fill factor, thereby enabling robust, high-efficiency devices.