24.64%-Efficiency MA-Free Perovskite Solar Cell with Voc of 1.19 V Enabled by a Hinge-Type Fluorine-Rich Complex

High density of defects at interface severely affects the performance of perovskite solar cells (PSCs). Herein, cobalt (II) hexafluoro-2,4-pentanedionat (CoFAc), a hinge-type fluorine-rich complex, is introduced onto the surface of formamidinium cesium lead iodide (FACsPbI(3)) film to address the issues of perovskite/Spiro-OMeTAD interface. The existence of CoFAc passivates both organic cation and halide anion vacancies by establishing powerful hydrogen bonds with HC(NH2)(2)(+) (FA(+)) and strong ionic bonds with Pb2+ in perovskite films. In addition, CoFAc serves as a connecting link to enhance interfacial hole-transport kinetics via interacting with Spiro-OMeTAD. Consequently, FACsPbI(3) PSCs with CoFAc modification display a champion power conversion efficiency (PCE) of 24.64% with a charming open-circuit voltage (V-OC) of 1.191 V, which is the record V-OC among all the reported organic-inorganic hybrid PSCs with TiO2 as electron transport layer. Furthermore, CoFAc-modified devices exhibit an outstanding long-term stability, which can maintain 95% of their initial PCEs after exposure to ambient atmosphere for 1500 h without any encapsulation.

Automated summary

High density of defects at the interface greatly affects the performance of perovskite solar cells (PSCs). In this study, a hinge-type fluorine-rich complex, cobalt (II) hexafluoro-2,4-pentanedionate (CoFAc), is introduced onto the surface of formamidinium cesium lead iodide (FACsPbI(3)) film to address the issues related to the perovskite/Spiro-OMeTAD interface. CoFAc passivates vacancies in the organic cation and halide anion by forming strong hydrogen bonds with HC(NH2)(2)(+) (FA(+)) and strong ionic bonds with Pb2+ in the perovskite film. Additionally, CoFAc improves interfacial hole-transport kinetics by interacting with Spiro-OMeTAD. As a result, FACsPbI(3) PSCs with CoFAc modification demonstrate a record power conversion efficiency (PCE) of 24.64% and an impressive open-circuit voltage (V-OC) of 1.191 V, the highest reported V-OC among all organic-inorganic hybrid PSCs with TiO2 as the electron transport layer. Furthermore, CoFAc-modified devices exhibit exceptional long-term stability, retaining 95% of their initial PCE after exposure to ambient atmosphere for 1500 hours without any encapsulation.