Organic ammonium halides enhance the performance of Pb-Sn perovskite solar cells

With the efforts of scientists around the world,the power conversion efficiency(PCE)of perovskite solar cells(PSCs)has reached 25.7%.To further improve the efficiency and break through the Shockley-Queisser(S-Q)limit,it is promising to construct all-perovskite tandem solar cells via combining wide-bandgap and narrow-bandgap perovskites[1−5].As the key light-harvesting material for the bottom cell in all-per-ovskite tandem devices,the narrow-bandgap Pb-Sn mixed per-ovskites have attracted increasing interest in recent years[6−8].However,the Pb-Sn mixed perovskites suffer from uncontrol-lable crystallization,easy oxidation of Sn2+and high defect density,which significantly limit PCE improvement[9,10].Organ-ic ammonium halides can improve the efficiency and stabil-ity of Pb-Sn mixed PSCs.