Using a Lewis base additive is essential for synthesizing uniform perovskite because it forms an intermediate phase during the perovskite solution process which slows the crystallization rate. Synthesizing CsFAPbI3 with a high concentration of cesium in an ambient environment, using dimethyl sulfoxide (DMSO) as a Lewis base additive, leads to the formation of δ-CsPbI₃, which reduces light absorption in the perovskite. To suppress δ-CsPbI₃ formation, this study utilizes N-methyl-2-pyrrolidone (NMP) as the Lewis base additive. The perovskite synthesized with NMP effectively suppresses δ-CsPbI₃. However, there is no significant difference in solar cell performance compared to those synthesized with DMSO. This lack of improvement can be attributed to the incompatible interaction between ethyl acetate and NMP, which increases non-radiative recombination and reduces carrier lifetime.

Keywords: Perovskite, Cesium, Solar cell, Dimethyl sulfoxide, N-methyl-2-pyrrolidone