Whether Addition of Phenethylammonium Ion is Always Beneficial to Stability Enhancement of MAPbI₃ Perovskite Film?

The recent studies widely believe that the stability of (PEA)₂PbI₄/MAPbI₃ perovskite solar cells (PSCs) can be progressively increased with the addition of phenethylammonium ion (PEA⁺). Herein, it is reported on the stability variations after the addition of PEA⁺ into the MAPbI₃ film and it is demonstrated that excess PEA⁺ has negative effect on the stability of (PEA)₂PbI₄/MAPbI₃ perovskite film. X-ray photoelectron spectroscopy, nuclear magnetic resonance, and X-ray absorption fine structure spectroscopy are utilized to testify that the excess PEA⁺ damages the MAPbI₃ crystal structure and generates defects due to the strong coordination between NH₃⁺ from PEA⁺ and I⁻ from [PbI₆]⁴⁻. This work reveals that the stability of (PEA)₂PbI₄/MAPbI₃ perovskite films is not proportional to the addition of PEA⁺, which is of interest for the developing of stable 2D/3D PSCs.