In Situ Polymerized Organic Salt Interlayer for Enhanced Performance in Printable Mesoscopic Perovskite Solar Cells

Achieving high efficiency in perovskite solar cells (PSCs) requires a stable and robust buried interface. In this work, a durable buffer layer at the buried interface of printable mesoscopic PSCs (p-MPSCs) is introduced by modifying the mesoporous TiO₂ electron transport layer with sodium thioctate (ST), a self-polymerizing organic salt. Under relatively mild conditions, ST undergoes in situ polymerization on the inner surface of TiO₂, forming a cross-linked poly(ST) interfacial buffer layer at the junction with the perovskite. This polymer layer enhances interface mechanical strength via electrostatic interactions. Additionally, the flexible polymer side chains help to alleviate interfacial residual stress, while carboxylate groups effectively passivate defects, thereby minimizing non-radiative recombination at the buried interface. The combined effects result in p-MPSCs with improved performance, achieving a power conversion efficiency of 20.33% and demonstrating improved operational stability by retaining >92% of their initial efficiency after 600 h of continuous maximum power point tracking.