Multi‐Facet Passivation of Ternary Colloidal Quantum Dot Enabled by Quadruple‐Ligand Ensemble toward Efficient Lead‐Free Optoelectronics

Solution‐processed ternary‐compound semiconductor AgBiS 2 colloidal quantum dots (CQDs) are promising light‐absorbing materials owing to their nontoxicity and high absorption coefficient (>10 6 cm −1 ). However, rational strategies to passivate multi‐facet of ternary‐compound CQDs and manufacture stable CQD inks have not yet been proposed. In this paper, a ligand passivation strategy is proposed using a solution‐phase ligand exchange method. A quadruple‐ligand ensemble is employed to demonstrate multifaceted passivation on AgBiS 2 CQDs and a highly stable CQD ink. Density functional theory studies reveal the secondary cation adsorption of silver halide passivation, indicating the synergistic passivation of the ligand ensemble. This yields a low trap density in CQD solids, improving the power conversion efficiency to 8.1% by 53% in CQD solar cells. Furthermore, the proposed device exhibits the fastest response time of 400 ns among all reported AgBiS 2 devices, demonstrating its potential for efficient lead‐free optoelectronics.