Multifunctional Self‐Assembled Ionic Liquid Modified Rigid and Flexible Substrates for Efficient Simple‐Structured Perovskite Solar Cells

The advancement of electron transport layer (ETL)‐free perovskite solar cells (PSCs) is crucial for the commercialization of PSCs. At present, the slow electron extraction and significant carrier recombination, related to the energy‐level alignment at the FTO/perovskite interface, restrict the performance of ETL‐free PSCs. The facile modification of bottom electrodes is pivotal for tackling these issues and stimulating the photovoltaic potential of perovskite. Herein, a cost‐competitive and neoteric 1‐hydroxyethyl‐3‐methylimidazolium chloride, [HOEtMIM]Cl, ionic liquid is employed to modify the surface of rigid and flexible electrodes, and thus enable an energetically well‐aligned interface with perovskite layer via the electric dipole effects. The resulting barrier‐free FTO/perovskite contact can tremendously ameliorate the electron extraction and collection, with mitigated nonradiative interfacial carrier recombination loss. Additionally, the lone pair on the nitrogen of the imidazole group passivates the surface defects of perovskite layers, and the chloride anion plays a role in the crystallinity improvement of perovskite. Leveraged by the [HOEtMIM]Cl modification, the resulting ETL‐free rigid and flexible devices deliver an outstanding power conversion efficiency of 19.60 % and 15.57 %, along with the ameliorated hysteresis and long‐term tenability. This finding highlights the drastic potential of the engineered [HOEtMIM]Cl in manufacturing stable and high‐performance ETL‐free PSCs for their scaled‐up production. Ionic liquids can do more! A facile and efficient self‐assembled [HOEtMIM]Cl layer is introduced for the first time in the rigid and flexible electron transport layer‐free perovskite solar cells, giving rise an improved power conversion efficiency of 19.60 % and 15.57 %, along with an improved hysteresis and stability.