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

Solution-processed ternary-compound semiconductor AgBiS2 colloidal quantum dots (CQDs) are promising light-absorbing materials owing to their nontoxicity and high absorption coefficient (>106 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 AgBiS2 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 AgBiS2 devices, demonstrating its potential for efficient lead-free optoelectronics.