Self-assembly of porphyrins on perovskite film for blade-coating stable large-area methylammonium-free solar cells

Phase transition and phase separation of formamidinium-cesium (FA-Cs) perovskite during the fabrication and operation processes reduce the efficiency and stability of perovskite solar cells (PSCs). Here, we develop an in situ molecular self-assembly approach on perovskite surface using an amine nickel porphyrin (NiP). The NiP doped perovskite precursor solution was deposited on substrate by blade-coating under ambient condition. NiP molecules self-assemble into supramolecule bound on perovskite surface during the vacuum-assisted process. Such a modification controls the perovskite grain growth to generate the uniform perovskite film. The supramolecule can release the residual lattice strain to inhibit the phase transition of perovskite film, and promote the charge extraction and transport to suppress the phase separation of FA-Cs perovskite during long-term illumination condition. Consequently, the best efficiency of large-area NiP-based FA-Cs-PSCs with the active area of 1.0 cm² is up to 20.3% (certified as 19.2%), which is close to the record efficiency (20.37%) by blade-coating. Unencapsulated NiP-doped device reveals the remarkably improved overall stabilities. This work affords a novel way to address the phase transition and phase separation in FA-Cs perovskite.