Spatial Atomic Arrangement of Cyclohexyl‐Based Ligands for Enhanced Interface Passivation in 2D/3D Perovskite Solar Cells

Metal halide perovskite solar cells (PSC) have emerged as a promising candidate for next-generation photovoltaic technologies, achieving remarkable power conversion efficiencies (PCE) in polycrystalline thin-films. Nonetheless, their PCE and long-term stability are often limited by a high density of defects at interfaces and grain boundaries. One effective strategy to mitigate these issues is forming 2D/3D heterojunction structure by introducing a surface-passivating interfacial layer of quasi-2D Ruddlesden-Popper perovskite (RPP) with various functional ligand molecules. In this study, hydroxyl-functionalized cyclohexyl ammonium hydrochloride (ACHACl) is employed as the ligand molecule, which features dual functional groups. A comparative analysis reveals that cis-configurations of the ligands exhibit enhanced adsorption on the [PbI₆]^4- octahedra in lead halide perovskites, enabling more effective passivation of defects including metallic Pb⁰ on 3D perovskite thin-films. Moreover, the 2D/3D structure incorporating the RPP improves hole extraction to the hole transport layer (HTL) by inducing an upward shift in the valence band edge. Consequently, the 2D/3D heterojunction PSCs achieve a PCE of 23% under 1-Sun illumination, along with significantly improved long-term stability, presenting the critical role of tailoring the atomic structure of the RPP ligand molecules to boost both the efficiency and long-term stability of PSCs.