Stabilizing Formamidinium Lead Iodide Perovskite Precursor Solution with Phenylboric Acid

The instability of the perovskite precursor solution seriously affects the purity of the perovskite films, which is one of the key factors for the low reproducibility for highly efficient devices. Formamidinium‐based perovskite with more suitable spectral absorption range and higher thermal stability has become the mainstream material. However, the side reactions in pure formamidinium lead iodide solution have not been fully revealed. Herein, it is demonstrated that self‐condensation of formamidinium iodide occurs to form the by‐product s ‐triazine, and its content increases with the aging time of the solution. It is also discovered that phenylboric acid (PBA) can effectively inhibit the self‐condensation reaction and the content of the s ‐triazine is decreased by more than 95% in the solution aging at 60 °C for 7 days. The PBA used as the stabilizer not only enhances purity and decreases defect density of the perovskite films but also strongly enhances the reproducibility for highly efficient perovskite solar cells.