Multifunctional Ion‐Lock Interface Layer Achieved by Solid–Solid Contact Approach for Stabilizing Perovskite Solar Cells

It has been a hindering issue in perovskite solar cells that the interfaces between the perovskite and charge transport layers show significantly high concentrations of defects with an amount about 100 times more than inside the bulk perovskite layer. The issue causes substantial reduction in both the efficiency and stability of the devices. Herein, a solid–solid contact approach is demonstrated to realize a multifunctional ion‐lock layer with strong chemical interaction to the perovskite layer. The multifunctional ion‐lock layer remarkably suppresses the interface defects and tunes the work function, contributing to promoting the carrier extraction, increasing the open‐circuit voltage, and enlarging the photocurrent. In addition, the multifunctional ion‐lock layer successfully locks ions from movement and thus improves the stability of the devices. Finally, with a multifunctional ion‐lock layer, the perovskite solar cells deliver an efficiency of up to 23.13% along with desirable long‐term operational, storage, and humidity stability. Consequently, the work offers guidelines for establishing defect‐suppressed interfaces between perovskites and hole transport layers. A solid–solid contact strategy is proposed to form an ultra‐thin multifunctional ion‐lock interface layer in PSCs. This dense Nafion layer can lock the ions migration between perovskite and CTLs and eliminate the surface defects/traps of perovskite. The PSCs with Nafion multifunctional ion‐lock interface layer show a high efficiency of 23.13% with excellent humidity and operational stability.