Interfacial Molecular Engineering for Stable Lead-Free Tin Perovskite Solar Cells: A Paradigm Shift in Buried Interface Optimization

• • The use of MBP as a self-assembled monolayer on NiOx yields a contact angle reduction from 70° (bare NiOx) to 30° with Sn-PVSK precursor, enhancing film uniformity and reducing interfacial defects, leading to improved fill factor and open-circuit voltage in tin perovskite solar cells. • • Replacing acidic PEDOT:PSS with NiOx/MBP hole transport layer eliminates acid-induced degradation of the perovskite layer, extending device operational lifetime by over 500 hours under continuous illumination (ISOS-L-1 protocol) compared to PEDOT:PSS-based devices. • • The optimized NiOx/MBP interface achieves a power conversion efficiency (PCE) of 14.2% for tin-based perovskite solar cells, a 20% relative improvement over devices with 2PACz or MBC SAMs, attributed to better energy level alignment and reduced non-radiative recombination. • • The molecular design of MBP, featuring a phosphonic acid anchoring group and a methyl-substituted biphenyl core, provides a dense, well-ordered monolayer that passivates under-coordinated tin atoms at the buried interface, reducing trap density by an order of magnitude (from 10^16 cm^-3 to 10^15 cm^-3) as measured by thermal admittance spectroscopy.