A Composite Interlayer Reconciling Mechanical and Electrical Stability in Perovskite Solar Cells

Interfacial instability of n-type contacts remains a key barrier to the commercialization of perovskite solar cells (PSCs), as coupled lattice stress and ion migration rapidly deteriorate electronic order and structural integrity. Here, we report a fully solution-processed n-type interfacial architecture that unifies mechanical compliance, electronic stabilization, and thickness-insensitive operation. A thermally in situ self-crosslinked bathocuproine derivative (c-BCP) is integrated with a π-conjugated n-type conductive ink (PBFDO:PEOx) to form a mechanically continuous yet electronically selective junction that remains effective across thicknesses approaching 60 nm. This composite interlayer effectively redistributes interfacial stress, suppresses halide migration, and minimizes defect-assisted nonradiative recombination. By coupling elastic energy dissipation with directional charge transport, the design resolves the long-standing trade-off between interfacial robustness and carrier extraction in n-type contacts. Devices incorporating this interlayer deliver a champion efficiency of 26.37% and retain >92% of their initial performance after 1000 h of continuous illumination under thermal stress. These results establish a generalizable and manufacturing-ready framework for thick, solution-processable n-type contacts, enabling intrinsically durable and high-efficiency perovskite optoelectronics.