Lewis Base-Functionalized Imidazolium Ionic Liquid Interface Layers in Scalable Nickel Oxide-Based Perovskite Solar Cells

Interfacial defects at the NiOx/perovskite heterojunction are widely recognized as a critical bottleneck limiting the efficiency and long-term stability of perovskite solar cells (PSCs). In this study, a series of functionalized ionic liquids (FILs) with Lewis basic groups (amide, thioester, ester) covalently attached to the imidazolium core have been prepared as the tetrafluoroborate (BF4–) salt and evaluated as interfacial layer materials for the NiOx/perovskite interface. The Lewis base groups of the FILs passivate under-coordinated Pb2+ centers in the perovskite lattice, forming Lewis acid–base adducts that suppress nonradiative recombination pathways and promote charge extraction as evidenced from photoluminescence and electrochemical impedance spectroscopy studies. Devices were fabricated on flexible substrates with all inorganic charge transport layers, NiOx and SnO2, and the FILs at the NiOx/perovskite interface via a scalable blade-coating method. The inclusion of the FIL interfacial layers enhanced the film quality, reduced the interfacial resistance, and improved charge transport. As a result, the passivated PSCs with amide FIL deliver a champion power conversion efficiency (PCE) of ∼17.45% with an average PCE of 16.27% along with extended operational stability (T75) over 20 days of continuous illumination at 50 °C. Overall, this work highlights how optimal interfacial modifiers that promote the formation of Lewis acid–base adducts can be utilized for the fabrication of scalable p-i-n PSC devices with all inorganic CTLs to promote efficient electronic coupling to maximize charge extraction, suppress recombination, and enhance both PCE and operational stability.