A reaction-and-assembly approach using monoamine zinc porphyrin for highly stable large-area perovskite solar cells

Inhibiting the irreversible escape of organic cations and iodide species in perovskite films is crucial for the fabrication of efficient and stable perovskite solar cells(PSCs).Here,we develop a reaction-and-assembly approach using monoamine zinc porphyrin(ZnP)to modify methylammonium(MA^+)lead iodide perovskite film.The amine group in ZnP reacts with MA^+and I^-ions to yield monoammonium zinc porphyrin(ZnP-H+I-).The resultant films show no escape of iodide when immersed in ether solutions.Measurements from space-charge limited currents and transient photoluminescence indicate the modified films have reduced density of defects.These results suggest the formed ZnP-H^+I^-is bound on the surface and grain boundary of perovskite film to retard migrations of ions.DFT calculations also show that the energy alignment between ZnP-H^+and perovskite facilitates the electron transfer and reduces charge recombination at the perovskite grains.Furthermore,post-treating the Zn Pdoped film with ZnP again results in the formation of a one dimension zig-zag coordination polymer on the surface of the perovskite film.The single crystal structure of ZnP shows the polymer layer is formed through the coordination interaction between the Zn(II)metal center and a neighboring monoamine.The polymer facilitates the interfacial charge transfer,and reduces the escape of organic cations and iodide species in perovskite films,thereby keeping the excellent cell performance(20.0%)and further realizing the ion encapsulation.Finally,the modified PSCs retain over 90%of its original efficiency over2,000 h at 85°C or AM 1.5 G continuous illumination,or over 6,000 h in 45%humidity without encapsulation.This work affords a new strategy to achieve the efficient ions immobilization and encapsulation by in situ reaction and coordination assembly of mono-amine zinc porphyrin.