All-inorganic CsPb1-xSnxI2Br perovskites mediated by dicyandiamide additive for efficient 4-terminal tandem solar cell

Sn-Pb mixed perovskite solar cells (PSCs) have attracted research attention due to their application in tandem solar cells, but suffered from pin-hole morphology and device instability. In this work, dicyandiamide (DCD) is used as an antioxidative additive to regulate the crystallization and passivation of all-inorganic CsPb1-xSnxI2Br film. The strong coordination bonding between DCD and Pb/Sn not only effectively eliminates the pin-holes but also inhibits the oxidation of Sn2+ at low temperature. The power conversion efficiency (PCE) of inverted PSC (ITO/NiOx/CsPb0.6Sn0.4I2Br:DCD/ZnO/PC61BM/Ag) is improved from 10.53% to 14.17% (0.1 cm2), which is also one of the highest efficiencies of all-inorganic Sn-Pb mixed PSC. Meanwhile, compare with the control devices, the target device exhibits better stability after a series of tests. In addition, combining semitransparent 1.92-eV-bandgap top PSC (ITO/NiOx/CsPbI2Br:DCD/Ti0.9Sn0.1O2/IZO/MgF2) with CsPb0.6Sn0.4I2Br:DCD (1.54 eV) bottom PSC, an efficiency of 19.61% is demonstrated in all-inorganic 4-terminal (4T) tandem PSC. This work paves the way towards efficient all-inorganic perovskite tandem solar cells.