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

Abstract

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 ZnP-doped 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 over 2,000 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.