Intralayer Bidentate Ligand Design for Enhanced Stability in 2D Perovskites

Traditional ligands in two-dimensional (2D) perovskites are primarily dominated by monodentate Ruddlesden-Popper (R-P) phase ligands and interlayer bidentate Dion-Jacobson (D-J) phase ligands. In this study, we designed and synthesized a novel intralayer bidentate ligand, named MeX, referred to as the L-D (Lin-Dou) phase ligand. Single crystal X-ray diffraction (XRD) analysis of 2D lead bromide perovskites incorporating this MeX ligand ((MeX)PbBr₄) reveals that its two ammonium groups anchor adjacent cation sites within the same inorganic layer, a distinct characteristic compared to D-J phase ligands that connect between layers.
Temperature-dependent XRD and photoluminescence studies indicate a phase transition around 170–190 K, attributed to ligand reconfiguration within the organic layer. Comparative studies on polycrystalline perovskite thin films demonstrate that the L-D phase ligand shows significantly improved thermal stability compared to R-P and D-J ligands. Stability tracking under thermal annealing at 85°C shows that films employing the L-D phase ligand exhibit a T₈₀ lifetime improvement of 1600% and 140% over those utilizing R-P and D-J ligands, respectively.
Furthermore, incorporating (MeX)I₂ as a modified ligand in n-i-p perovskite solar cells resulted in a power conversion efficiency (PCE) of 25.31%, along with enhanced long-term stability compared to devices with R-P and D-J ligands. These results underscore the broad performance advantages of the L-D phase ligand for 2D perovskite applications.