Fluorine Functionalized MXene QDs for Near‐Record‐Efficiency CsPbI3 Solar Cell with High Open‐Circuit Voltage

Abstract CsPbI 3 inorganic perovskites have attracted significant attention due to their desirable bandgap for tandem solar cells and excellent thermal stability. However, CsPbI 3 perovskite solar cells (PSCs) still exhibit low efficiency and high energy loss due to nonradiative recombination. Herein, functionalized Ti 3 C 2 F x quantum dots (QDs) are prepared and selected as interface passivators to enhance the performance of CsPbI 3 PSCs. The systematic experimental results reveal that Ti 3 C 2 F x QDs serve as effective passivators mainly in three aspects: 1) p ‐type Ti 3 C 2 F x QDs can tune the energy level of perovskite films and provide an efficient pathway for hole transfer; 2) Ti 3 C 2 F x QDs can effectively passivate defects and reduce interfacial nonradiative recombination, and 3) Ti 3 C 2 F x QDs form a barrier layer to prevent water invasion and improve the stability of CsPbI 3 PSCs. Consequently, the champion CsPbI 3 PSC with Ti 3 C 2 F x QDs treatment exhibits an excellent efficiency of 20.44% with a high open‐circuit voltage of 1.22 V. Meanwhile, the corresponding device without encapsulation retained 93% of its initial efficiency after 600 h of storage in ambient air.