Triple-Functional Hybrid Self-Assembled Monolayer for Efficient and Stable Inverted Wide-Bandgap Perovskite Solar Cells with Suppressed Lead Leakage

In inverted perovskite solar cells, self-assembled monolayers (SAMs) are often used as hole-transport layers; traditional SAMs like [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), however, do not cover the surface completely, have many defects at the interface, and cannot effectively stop Pb2+ migration, which lowers device efficiency and stability. We prepare a mixed self-assembled monolayer blending 4'-carboxybenzo-18-crown-6 (CB18C6) and Me-4PACz. The crown ether coordinates with Pb2+ via oxygen atoms to suppress lead leakage, while its phenyl groups π-π stack with Me-4PACz carbazole units for uniform, ordered surfaces. Terminal carboxyl groups fill film voids to smooth surfaces and unify surface potential. The optimized wide-bandgap perovskite solar cell (energy gap (Eg) ≈ 1.66 eV) reaches 21.08% efficiency. Unencapsulated devices maintain >90% efficiency under ISOS-D-1 and ISOS-D-2 tests with negligible aqueous Pb2+ leakage. This work proposes an innovative interlayer design integrating passivation and lead immobilization for stable perovskite photovoltaics.