A Dual‐Functional Molecule for Efficient and Stable CsPbI₃‐Based 2D Dion–Jacobson Perovskite Solar Cells

Herein, a new type of CsPbI 3 ‐based 2D Dion–Jacobson (DJ) perovskites is reported, featuring a general formula of (PDMA)Cs n −1 PbnI 3 n +1 ( n = 1, 2, 3, 4) with 1,4‐phenylenedimethanammonium (PDMA) as the organic spacer cation. The crystal structure, optical and electric properties, and surface morphology of the perovskite films are fully surveyed. The solar cell device based on the n = 4 film delivers a champion power conversion efficiency (PCE) of 11.27%, further improved to 12.61% by treating with the PDMA molecules. The PDMA passivation suppresses non‐radiative recombination, extends charge‐carrier lifetime, and reduces open‐circuit voltage loss. A gradient energy level near the film surface facilitates electron extraction, alleviating charge accumulation. The PDMA molecules form a protective layer, inhibiting water infiltration and enhancing stability. The optimized device exhibits excellent shelf stability with no PCE decay after 110 days. In this study, a dual‐functional molecule is introduced as a new DJ‐type spacer and an effective passivation agent for efficient and stable CsPbI 3 ‐based 2D perovskite solar cells.