Suppressed Intermolecular Interaction Between Organic Spacers for High‐Performance p‐i‐n and n‐i‐p Perovskite Solar Cells

Abstract Ammonium cations are widely used for defect passivation in perovskite solar cells (PSCs), effectively reducing defect density and improving photovoltaic performance. However, ammonium cations tend to form 2D phases on the surface or at the grain boundaries of 3D perovskites, hindering charge transport across interfaces and between grains. Here, cyclohexylmethylammonium (CHMA⁺), a low‐polarity and low‐rigidity alicyclic ammonium cation, is introduced to reduce intermolecular interactions among ammonium cations and improve their coordination with defect centers. In contrast, a structure‐similar phenylethylammonium cation (PEA⁺) with a conjugated π‐bond system, higher polarity, and larger structure rigidity, exhibits strong intermolecular π–π interaction and facilitates the formation of quasi‐2D phases via cation exchange. These quasi‐2D phases exhibit non‐uniform longitudinal distribution in the 3D perovskite layer, thereby compromising the charge extraction efficiency. The CHMA⁺‐modified perovskite‐based devices with p‐i‐n and n‐i‐p structures achieve impressive power conversion efficiencies of 25.66% (certified 24.64%) and 24.94%, respectively. Moreover, the device maintains over 95% of its initial efficiency after 1000 h of continuous operation under one‐sun illumination at the maximum power point. These findings highlight the potential of rationally designing ammonium spacers to significantly improve both the efficiency and stability of PSCs.