Self‐Assembled Ionic Liquid for Highly Efficient Electron Transport Layer Free Perovskite Solar Cells

The electron-transport-layer (ETL) free perovskite solar cells (PSCs) are attractive because of fewer layers and hence lower cost, but the lower photovoltaic performance, as compared to the ETL-contained PSCs, largely restricts their practical applications. Herein, we design and synthesize hydroxylethyl functionalized imidazolium iodide, whose single crystal structure is determined, and propose self-assembled ionic liquid on the conductive substrate for ETL-free PSCs. It is found that the self-assembly of the ionic liquid on the conductive substrate can lower the work function of the conductive substrate, enhance the interfacial electron extraction, and meanwhile retard the interfacial charge recombination. As a consequence, the power conversion efficiency is improved remarkably from 9.01% to 17.31% upon the self-assembly of ionic liquid on the conductive substrate. This finding provides a new way to achieve highly efficient ETL free PSCs.