In this study, the reproducibility of perovskite solar cell (PSC) performance is improved through ethylenediammonium (EDA2+)‐based surface treatments. By substituting iodide in EDAI2 with larger anions, such as thiocyanate (SCN–), tetrafluoroborate (BF4–), and hexafluorophosphate (PF6–), we significantly increased the solubility of EDA2+ in isopropyl alcohol (IPA), thereby enhancing the reliability of the compositions at the working concentrations by avoiding the risk of unwanted precipitation. In p–i–n‐type lead‐based PSCs, the standard deviation of power conversion efficiency (PCE) was reduced from 2.1% with EDAI2 to 0.7% with EDA(SCN)2, 0.7% with EDA(BF4)2 and, 0.4% with EDA(PF6)2. The high solubility of EDA(PF6)2 in low‐polarity solvents such as ethyl acetate facilitated damage‐free surface modifications, as demonstrated by successful application to mixed tin–lead PSCs. These findings show how tailored anion substitution in EDA2+ solutions enhances the consistency and performance of PSC surface treatments.
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