A Crystalline 2D Fullerene‐Based Metal Halide Semiconductor for Efficient and Stable Ideal‐bandgap Perovskite Solar Cells

Abstract Despite advances in mixed tin‐lead (Sn‐Pb) perovskite‐based solar cells, achieving both high‐efficiency and long‐term device stability remains a major challenge. Current device deficiencies stem partly from inefficient carrier transport, originating from defects and improper band energy alignment among the device's interfaces. Developing multifunctional interlayer materials simultaneously addressing the above concerns poses an excellent strategy. Herein, through molecular and crystal engineering, an amine‐functionalized C 60 mono‐adduct derivative (C 60 ‐2NH 3 = bis(2‐aminoethyl) malonate‐C 60 ) is utilized for the synthesis of the first crystalline fullerene‐based 2D metal halide semiconductor, namely (C 60 ‐2NH 3 )Pb 2 I 6 . Single crystal XRD studies elucidated the structure of the new material, while DFT calculations highlighted the strong contribution of C 60 ‐2NH 3 to the electronic density of states of the conduction band of (C 60 ‐2NH 3 )Pb 2 I 6 . Utilization of C 60 ‐2NH 3 as an interlayer between a FA 0.6 MA 0.4 Pb 0.7 Sn 0.3 I 3 perovskite and a C 60 layer offered superior band energy alignment, reduced nonradiative recombination, and enhanced carrier mobility. The corresponding perovskite solar cell (PSC) device achieved a power conversion efficiency (PCE) value of 21.64%, maintaining 90% of its initial efficiency, after being stored under a N 2 atmosphere for 2400 h. This work sets the foundation for developing a new family of functional materials, namely Fullerene Metal Halide Semiconductors, targeting applications from photovoltaics to catalysis, transistors, and supercapacitors.