Multi-Facet Passivated AgBiS₂ Colloidal Quantum Dot for Efficient Lead-Free Optoelectronic

Silver bismuth sulfide (AgBiS₂) colloidal quantum dots (CQD) are promising lead-free light absorbing materials for CQD optoelectronic due to their low cost, earth-abundant element, and high absorption coefficients. However, AgBiS₂ CQD photovoltaics are hampered by low open-circuit voltage (<i>V_oc</i>) due to the complication of passivating charge neutral (100) surface of AgBiS₂. Here, we propose a ligand combination for solution ligand exchange to passivate the (100) facet of the AgBiS₂ with improved ink stability. We demonstrated that incorporating alkali metal ions can enhance the ink stability of solution ligand exchanged CQD ink and surface ligand coverage ratio. We revealed the synergetic passivating mechanism of cation ligands on AgBiS₂ CQD surface through density functional theory. This multi-facet passivated AgBiS₂CQD solid possessed low trap density and Urbach tail. Consequently, fabricated multi-facet passivated AgBiS₂optoelectronics showed power conversion efficiency (PCE) of 8.1 %, detectivity of over 10¹¹ around 400-930 nm, and response time of 400 ns. Which is the highest PCE and fastest response time among published solution ligand-exchanged AgBiS₂ optoelectronics showing promise for lead-free optoelectronics.