Over 20% Efficiency in Printable Mesoscopic Perovskite Solar Cells with Enhanced Open‐Circuit Voltage via a Multifunctional Ionic Liquid

The large open-circuit voltage (V_OC) losses limit the enhancement of power conversion efficiency (PCE) in printable mesoscopic perovskite solar cells (p-MPSCs). These losses primarily result from the high defect density at perovskite grain boundaries within the mesoporous scaffold, which promotes non-radiative recombination. In this study, the crystallization improvement and defect modulation of perovskite is promoted by adopting a multifunctional ionic liquid, 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate (BMMIm[OTF]). The imidazolium ions in BMMIm[OTF] form hydrogen bonds with the PbI₆ ^4- framework and coordinate with under-coordinated lead ions through S═O bonds. These interactions synergistically improve the crystallinity of perovskite films and optimize energy level alignment at the perovskite/carbon electrode interface. This improved interface facilitates more efficient charge transfer and extraction while reducing non-radiative recombination. As a result, the champion p-MPSCs incorporating BMMIm[OTF] achieve a PCE of 20.02% and a V_OC of 1.055 V, significantly outperforming control devices with a V_OC of 0.965 V. Furthermore, the hydrophobic nature of BMMIm[OTF] enhances device stability. This research provides a practical strategy for developing efficient and durable p-MPSCs.