Bidentate Ligand Synergy Enables Homogeneous Perovskite Films for Efficient Cs ₂ AgBiBr ₆ Solar Cells

Lead-free double perovskite Cs2AgBiBr6 is a promising candidate for environmentally friendly perovskite solar cells (PSCs), providing an alternative to their toxic lead-based counterparts. However, rapid crystallization and facile Br/Ag vacancy formation lead to inhomogeneous films with high trap density and disordered heterojunctions, severely limiting device performance. Herein, we develop a synergistic modification strategy using bidentate ligand RbSCN. The incorporation of RbSCN into the SnO2 precursor mitigates buried interface defects, which improves interfacial contact. Simultaneously, bidentate ligand RbSCN added to the Cs2AgBiBr6 precursor leverages its bidentate coordination capability, targeted anchoring Ag+/Bi3+ cations separately at the stoichiometric ratio, inducing ordered assembly. This facilitates homogeneous crystallization and the efficient passivation of Br vacancies. Consequently, this synergistic modification strategy yields homogeneous films with superior charge transport properties, enabling PSCs to achieve an enhanced champion power conversion efficiency of 2.16% along with exceptional stability. This work underscores homogeneous film formation as being crucial for double perovskites and provides a clear pathway for optimizing lead-free PSCs.