Efficient and Stable Mesoporous CsSnI3 Perovskite Solar Cells via Imidazolium-Based Ionic Liquid Additive

Inorganic tin halide perovskite compound with its eco-friendly property has attracted tremendous attention of researchers in the field of lead-free perovskite solar cells. However, the trap-assisted nonradiative recombination caused by deep-level defects originating from surface undercoordinated Sn2+ cations significantly deteriorates the CsSnI3 device's performance. Herein, adding low concentrations of an ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc) shows promise in controlling deep-level defects in CsSnI3 perovskites. Both experimental observation and theoretical simulation reveal that EMIMAc can have strong electrostatic attraction and coordination interaction with the surface undercoordinated Sn2+ through the lone electron pairs of carboxyl functional groups and the donated pi electrons from electron-rich imidazole moieties, leading to a reduced deep-level defect density and a restrained nonradiative recombination. Consequently, the processed CsSnI(3 )perovskite solar cells based on a printable fluorine-doped tin oxide/compact-TiO2/mesoporous-TiO2/Al2O3/NiO/carbon framework achieve a power conversion efficiency as high as 8.54%, which is the champion efficiency among all the reported CsSnI3 mesoporous perovskite solar cells up to now. In addition, the unencapsulated devices have shown an impressive long-term stability with only approximate to 6% efficiency degradation after over 2000 h aging under nitrogen atmosphere.

Automated summary

In this study, the addition of low concentrations of an ionic liquid, 1-ethyl-3-methylimidazolium acetate (EMIMAc), was found to effectively control deep-level defects in CsSnI3 perovskites, leading to improved performance of the solar cells. Experimental observations and theoretical simulations showed that EMIMAc can interact with and attract the surface undercoordinated Sn2+ ions, reducing the density of deep-level defects and suppressing nonradiative recombination. As a result, the CsSnI3 perovskite solar cells achieved a high power conversion efficiency of 8.54%, making them the most efficient reported CsSnI3 mesoporous perovskite solar cells to date.