Engineered PB20 Discotic Interlayer Enabling Interfacial Passivation and Enhanced Performance–Stability in Perovskite Solar Cells

Perovskite/Spiro-OMeTAD interfaces in perovskite solar cells (PSCs) suffer from high defect densities, poor wettability, and dopant-induced degradation, which limit charge extraction and long-term stability. Herein, we engineer a multifunctional interfacial passivation layer based on a discotic columnar liquid crystal, antibis(4,5-dialkoxybenzimidazole) (PB20), to simultaneously mitigate interfacial defects and enhance environmental stability. The self-assembled PB20 interlayer forms a uniform, ordered interface that reduces recombination, improves surface morphology, and facilitates efficient hole transfer through favorable energy-level alignment. PB20-treated devices exhibit enhanced charge transport, reflected by a reduced trap density of ∼14% and an increased hole mobility (2.90 × 10–3 cm2 V–1 s–1). Consequently, the devices achieve an efficiency of 19.77%, representing an ∼14% improvement over pristine cells. The hydrophobic alkoxy side chains further impart strong moisture resistance, enabling PB20-modified devices to retain 82% of their initial efficiency after 60 days. These findings demonstrate PB20 as an effective engineered interlayer that enhances both the performance and the operational stability in PSCs.