Dual facet passivation of silver halometallate for eco-friendly silver bismuth sulfide near IR photodetector

[Display omitted] •AgBr as auxiliary ligand for improved surface passivation of AgBiS2 nanocrystals.•DFT study demonstrates strong AgBr2- binding at (100) surface compared to AgI2-.•Reduction of in-gap states densities through AgBr inclusion.•Greater responsivity at high photoconductive bias of −1V for dual passivated AgBiS2.•High performance photodetector devices with detectivity 1.8 × 1012 at 800 nm. Ternary chalcogenide silver bismuth sulfide nanocrystals (AgBiS2 NCs) have taken great strides in the past few years to emerge as one of the better eco-friendly alternatives to compete with the prevalent toxic semiconductor materials such as lead sulfide quantum dots (PbS QDs) in the near-infrared (NIR) region. Nevertheless, their implementation in photodetectors has been scarce due to high dark current and complicated solid-state ligand exchange fabrication steps involved, resulting in a lower overall detectivity. The performance is further deemed to be stunted due to the difficulty associated with the passivation of the charge-neutral (100) facet of larger AgBiS2 NCs efficiently. In this work, we aimed to develop a mixed ‘halometallate’ ligand approach, wherein we introduce silver bromide (AgBr) as an ancillary ligand to silver iodide (AgI), passivating both (100) and (111) facets of cubic AgBiS2 solids in a facile solution-phase ligand exchange step to obtain highly dispersible colloidal ink. Decreased bond length, bond angle (Br-Ag-Br), and ionic size of [AgBr2-] anion induces less compressive strain compared to [AgI2–], culminating in higher molecular stability on the AgBiS2 surface. This dual passivation reduces the dark current to 6.01 × 10-7 A cm−2 and a high specific detectivity of 1.8 × 1012 Jones at 800 nm is achieved, comparable to ubiquitous PbS QD devices. We also demonstrate diminished in-gap carrier density population, enhanced light detection, and ultrafast microsecond response at higher wavelengths operating under high bias (-1V) photoconductive mode. This study illustrates the role of optimum surface coverage in eliminating the deleterious non-radiative recombination defect centers by introducing additional ligands in solution-processed AgBiS2 NC and the viability of the mixed ligand approach for stable eco-friendly NIR photodetectors.