Application of Cesium on the Restriction of Precursor Crystallization for Highly Reproducible Perovskite Solar Cells Exceeding 20% Efficiency

In this study, we systematically explored the mixed-cation perovskite Csx(MA0.4FA0.6)1–xPbI3 fabricated via sequential introduction of cations. The details of the effects of Cs+ on the fabrication and performance of inorganic–organic mixed-cation perovskite solar cells examined in detail in this study are beyond the normal understanding of the adjusting band gap. It is found that a combined intercalation of Cs+ and dimethyl sulfoxide (DMSO) in PbI2–DMSO precursor film formed a strong and steady coordinated intermediate phase to retard PbI2 crystallization, suppress yellow nonperovskite δ-phase, and obtain a highly reproducible perovskite film with less defects and larger grains. The Cs-contained triple-cation-mixed perovskite Cs0.1(MA0.4FA0.6)0.9PbI3 devices yield over 20% reproducible efficiencies, superior stabilities, and fill factors of around 0.8 with a very narrow distribution.