CsF improved buried interface for efficient and stable inverted all-inorganic CsPbI2.85Br0.15 perovskite solar cells

All-inorganic CsPbIxBr3-x is frequently used as the top cells in tandem devices due to its tunable bandgap, making it highly promising for future development. However, CsPbIxBr3-x films typically contain numerous defects at the interfaces and grain boundaries, significantly hindering carrier transport and thus reducing the device performance. Interface modification is commonly employed to passivate defects and enhance carrier transport at the interfaces. In this work, CsF was used to modify the buried interface between the perovskite film and self- assembled monolayers (SAMs). The interaction between fluoride ions (F-) and uncoordinated Pb2+ contributed to reduce defect density, enhance crystallization quality, and suppress non-radiative carrier recombination at buried interface. Consequently, the efficiency of inverted CsPbI 2.85 Br 0.25 PSCs with CsF improved from 16.15 % to 18.24 %, compared to the control device. Moreover, the unencapsulated CsF-modified device retained 89 % of its initial efficiency after storing for 600 h in ambient air with room-temperature and relative humidity (RH) of 20 %. This demonstrates that CsF modification significantly enhances both the performance and stability of CsPbI 2.85 Br 0.15 perovskite solar cells.