Mixed-Ligand-Driven Phase-Pure 2D Perovskite for Interfacial Passivation of Perovskite Photovoltaics.

Effective interfacial passivation is essential for achieving high-performance perovskite photovoltaics. 2D/3D heterostructures are a widely adopted strategy for defect passivation and band alignment regulation. Despite recent progress, achieving favorable interfacial energetics and comprehensively suppressing nonradiative recombination at both surfaces and grain boundaries continues to be an active area of investigation. We introduce a coassembled 2D architecture in which long-chain ligands are complemented by a minority component of short-chain ligands to form a mixed-ligand passivation layer. Such a coassembled structure promotes preferentially phase-pure, n = 2, 2D layer formation, resulting in an energetically favorable band alignment that enhances charge extraction. In addition, this coassembly facilitates effective passivation of interfacial defects at both surfaces and grain boundaries, leading to suppressed nonradiative recombination. As a consequence, these interfacial improvements increase carrier lifetimes and enhance the fill factor and open-circuit voltage of the device, yielding a higher power-conversion efficiency.