Stability of Precursor Solution for Perovskite Solar Cell: Mixture (FAI + PbI2) versus Synthetic FAPbI3 Crystal

. For the single crystal solution, basic conditions remained unchanged by aging. In addition, the presence of δ-phase in the annealed perovskite films was found to have negative influence on the long-term stability. It is thus important to maintain the pH of the precursor solution to avoid aging effects and remove δ-phase in the annealed film for device stability.