Dongeon Kim¹,Gaeun Cho^1,2,Yun Hoo Kim³,Ji Hyun Kwon¹,YeonWoo Oh¹,Minjung Yang¹,Seungin Jee¹,In Suh Lee¹,Min-Jae Si¹,Yujin Jung⁴,Ho Yeon Yang¹,Changjo Kim⁵,Han Seul Kim⁶,Se-Woong Baek¹

Korea University¹,Korea Institute of Science and Technology Information²,Korea Institute of Science and Technology³,National University of Singapore⁴,Los Alamos National Laboratory⁵,Chungbuk National University⁶

Abstract

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 (Voc) 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 AgBiS2 CQD solid possessed low trap density and Urbach tail. Consequently, fabricated multi-facet passivated AgBiS2 optoelectronics 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.