Mechanism study on performance enhancement of inverted perovskite solar cells via 5-nitro-2-(3-pyridyl)benzimidazole molecular interface modification

Defects on the surface and at grain boundaries of perovskite films induce non-radiative recombination and deteriorate device performance in perovskite solar cells (PSCs). Eliminating these defects is therefore essential to improving efficiency. In this work, 5-nitro-2-(3-pyridyl)benzimidazole (NPBIm), a commercially available small molecule featuring a donor–π–acceptor push–pull architecture, is employed as a surface modifier for inverted PSCs. The pyridyl and benzimidazole nitrogen atoms coordinate with undercoordinated Pb 2+ ions, while the nitro group contributes to interfacial dipole formation, as supported by the observed work-function shift and UPS-derived energy-level realignment. NPBIm treatment after perovskite crystallization is associated with improved crystallinity, enlarged grain size (from 250.22 to 278.37 nm), and reduced defect density (from 1.32 × 10 16 to 1.08 × 10 16 cm −3 ). The slope of the Voc–ln(I) curve decreases from 1.39 kT/q to 1.24 kT/q, and carrier lifetime extends from 64.94 to 255.79 ns, indicating suppressed non-radiative recombination. The champion device achieves a PCE of 21.28%, surpassing the 19.56% of the control. Water contact angle tests indicate improved hydrophobicity and stability, with 65% efficiency retained after 400 h of ambient storage compared with 42% for the untreated device. These results suggest that NPBIm functions as an effective bifunctional interfacial modifier, concurrently passivating defects and optimizing band alignment in PSCs. • NPBIm tunes crystal growth, reduces defects, yielding compact, crystalline films. • Lewis-base and dipole alignment lower work function, enhancing extraction. • NPBIm boosts carrier dynamics and PCE to 21.28% vs 19.56%. • NPBIm passivation boosts PSC performance, cuts J–V hysteresis.