Self-Assembled Bilayers with Improved Solvent Resistance for Stable Inverted Perovskite Solar Cells

The self-assembled monolayer (SAM) molecules on ITO or metal oxide transporting layers tend to desorb during perovskite film processing and device operation, leading to reduced power conversion efficiency (PCE) and device degradation. Developing effective strategies to stabilize SAMs at interfaces is therefore crucial for further improving the performance and stability of SAM-based perovskite solar cells (PVSCs). Here, a facile method is developed to construct robust self-assembled bilayers (SABs) by depositing cross-linkable organosilanes, n-propyltrimethoxysilane (PTMS) and (3-mercaptopropyl)trimethoxysilane (MPTMS), onto the widely used Me-4PACz SAM for NiO_x modification. Me-4PACz enables excellent hole extraction, suppresses interfacial reactions and recombination, while the cross-linked organosilane network forms a robust protective layer that prevents the solvent-induced SAM desorption and fills molecular voids, yielding a more compact and stable interface. In addition, the thiol group in MPTMS can strongly interact with the undercoordinated Pb²⁺ at the buried interface of perovskite, further mitigating interfacial defects. Consequently, NiO_x/Me-4PACz/MPTMS based PVSCs achieve a high PCE of 24.9% with a T₈₀ lifetime of 475 h under continuous 1 sun equivalent illumination in air, compared to 23.3% and tens of hours for NiO_x/Me-4PACz-based control device. This work provides important insights into designing robust interfaces for high-performance and highly stable PVSCs.