Conjugated Hydrazide-Mediated Precursor Coordination Regulation Enables Uniform Crystallization of Tin-Lead Perovskites.

Narrow-bandgap tin-lead (Sn-Pb) mixed perovskites are important materials for advancing single-junction photovoltaics toward their theoretical efficiency limit. However, their inherent asynchronous crystallization triggers severe morphological inhomogeneity and generates a high defect density, which limits the performance and long-term stability of devices. Unlike conventional Lewis base strategies that predominantly focus on direct bonding effects for simple defect passivation, we propose a strategy for precursor colloidal regulation mediated by aromatic conjugated hydrazide derivatives. Extending the conjugation length of the hydrazide molecular framework established preferential coordination interactions between the additive and SnI2 precursor. This preferential complexation alleviated the aggregation of perovskite clusters and inhibited the rapid precipitation of Sn species, while simultaneously suggesting a lowered apparent heterogeneous nucleation energy barrier on the substrate. This approach achieved uniform and balanced Sn/Pb crystallization kinetics, which enabled the formation of compact, pinhole-free perovskite films. The optimal device modified with 2-naphthoylhydrazine delivered a power conversion efficiency of 24.16%, along with significantly enhanced operational stability, which retained 88.2% of its initial efficiency after 1200 h of continuous illumination. This work offers novel insights into precisely regulating the crystallization of narrow-bandgap Sn-Pb perovskites to enable the development of efficient and stable perovskite photovoltaics.