Counteranion Engineering of Ethylenediammonium Salts for Reproducible Surface Modification in p–i – n Perovskite Solar Cells

In this study, the reproducibility of perovskite solar cell (PSC) performance is improved through ethylenediammonium (EDA 2+ )‐based surface treatments. By substituting iodide in EDAI 2 with larger anions, such as thiocyanate (SCN – ), tetrafluoroborate (BF 4 − ), and hexafluorophosphate (PF 6 − ), we significantly increased the solubility of EDA 2+ 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 EDAI 2 to 0.7% with EDA(SCN) 2 , 0.7% with EDA(BF 4 ) 2 and, 0.4% with EDA(PF 6 ) 2 . The high solubility of EDA(PF 6 ) 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 EDA 2+ solutions enhances the consistency and performance of PSC surface treatments.