Amidinium-Based Ligand: The Next Generation Ligand for Dimensional Heterojunction Perovskite Photovoltaics

The operational stability of perovskite solar cells is limited by defects and instabilities at grain boundaries and buried interfaces in three-dimensional absorbers. Forming 3D/low-dimensional (LD) heterojunctions can improve both efficiency and durability, yet most LD layers use ammonium ligands that bind weakly to the lattice and can deprotonate, causing the LD layer to degrade under heat and illumination. This Perspective highlights amidinium-based organic ligands as a promising alternative for constructing more robust LD capping layers. Their planar, multivalent, resonance-stabilized headgroups enable stronger lattice interactions and reduced deprotonation. Although still emerging, tailoring the ligand tail provides a versatile handle to tune dimensionality, interfacial energetics, strain, and electronic coupling toward efficient, stable LD perovskite heterojunction photovoltaics.