Over-18%-Efficiency Quasi-2D Ruddlesden-Popper Pb-Sn Mixed Perovskite Solar Cells by Compositional Engineering

Quasi-two-dimensional(2D) Pb-Sn mixed perovskites showgreat potential in applications of single and tandem photovoltaicdevices, but they suffer from low efficiencies due to the existenceof horizontal 2D phases. Here, we obtain a record high efficiencyof 18.06% based on 2D & LeftAngleBracket;n & RightAngleBracket; = 5 Pb-Sn mixed perovskites (iso-BA(2)MA(4)(Pb x Sn1-x )(5)I-16, x =0.7), by optimizing the crystal orientation through a regulation ofthe Pb/Sn ratio. We find that Sn-rich precursors give rise to a mixtureof horizontal and vertical 2D phases. Interestingly, increasing thePb content can not only entirely suppress the unwanted horizontal2D phase in the film but also enhance the growth of vertical 2D phases,thus significantly improving the device performance and stability.It is suggested that an increase of the Pb content in the Pb-Snmixed systems facilitates the incorporation of iso-butylammonium (iso-BA(+)) ligands in verticallyoriented perovskites because of the reduced lattice strain and increasedinteraction between the organic ligands and inorganic framework. Ourwork sheds light on the optimal conditions for fabricating stableand efficient 2D Pb-Sn mixed perovskite solar cells.

Automated summary

By optimizing the crystal orientation through a regulation of the Pb/Sn ratio, we achieved a record high efficiency of 18.06% for quasi-two-dimensional (2D) Pb-Sn mixed perovskite solar cells. Increasing the Pb content can suppress the unwanted horizontal 2D phase and enhance the growth of vertical 2D phases, leading to improved device performance and stability.