Anion‐Cation Synergistic Regulation of Low‐Dimensional Perovskite Passivation Layer for Perovskite Solar Cells

Abstract Mixing 2D and 3D perovskite together is an effective strategy to enhance the stability of perovskite solar cells (PSCs). This strategy has been widely used in many recent works. Typically, 2D layer is formed by introducing 2D spacer onto 3D surfaces through in situ intercalation reaction. However, this intercalation may not stop after the 2D layer is formed. Progressive migration of 2D spacer into 3D bulk leads to increased n‐values of 2D phases and deviation from optimized structural design. The high n‐value 2D perovskite is less stable than the low n‐value 2D perovskite and may be prone to degradation under external stresses. Here, a heteroatom ammonium ligand, thiomorpholine (SMOR) is found, which can effectively passivate the perovskite surface, and form a 1D phase or 2D phase depending on cation to anion ratio and the type of anions. Due to lower formation energy at 1:1 cation to anion ratio, 1D phase can prevent the formation of high‐n‐value 2D phase and show excellent thermal stability. The passivation of SMOR‐based 1D perovskite boosts the device efficiency to 25.6% (certified 24.7%). More importantly, the unpackaged device can maintain >80% of its initial efficiency after stable operation at 85 °C for 1000 h.