Stabilization of formamidinium lead iodide perovskite precursor solution for blade-coating efficient carbon electrode perovskite solar cells*

Formamidinium lead triiodide (FAPbI(3)) is a research hotspot in perovskite photovoltaics due to its broad light absorption and proper thermal stability. However, quite a few researches focused on the stability of the FAPbI(3) perovskite precursor solutions. Besides, the most efficient FAPbI(3) layers are prepared by the spin-coating method, which is limited to the size of the device. Herein, the stability of FAPbI(3) perovskite solution with methylammonium chloride (MACl) or cesium chloride (CsCl) additive is studied for preparing perovskite film through an upscalable blade-coating method. Each additive works well for achieving a high-quality FAPbI(3) film, resulting in efficient carbon electrode perovskite solar cells (pero-SCs) in the ambient condition. However, the perovskite solution with MACl additive shows poor aging stability that no alpha-FAPbI(3) phase is observed when the solution is aged over one week. While the perovskite solution with CsCl additive shows promising aging stability that it still forms high-quality pure alpha-FAPbI(3) perovskite film even the solution is aged over one month. During the solution aging process, the MACl could be decomposed into methylamine which will form some unfavored intermediated phase inducing delta-phase FAPbI(3). Whereas, replacing MACl with CsCl could effectively solve this issue. Our founding shows that there is a great need to develop a non-MACl FAPbI(3) perovskite precursor solution for cost-effective preparation of pero-SCs.