Improved Eco-Friendly Photovoltaics Based on Stabilized AgBiS₂ Nanocrystal Inks

AgBiS 2 nanocrystals (NCs) have emerged as attractive absorbers in eco-friendly photovoltaics because of their nontoxic components and high absorption coefficient. Native long-chain ligands of AgBiS 2 NCs should be replaced with short-chain ligands for their photovoltaics; however, conventional approaches have been performed using solid-state ligand exchange (SSLE), resulting in inhomogeneous NC aggregation, broad bandtail, large trap density, and resultantly low open-circuit voltage ( V OC ) in devices. Herein, we first report that long-chain ligands of AgBiS 2 NCs are replaced with halometallate-based short ligands via solution-phase ligand exchange (SPLE). AgI and BiI 3 are used as halometallate sources, and we find that colloidally stable, highly concentrated AgBiS 2 NC inks in polar solvents are prepared via SPLE using AgI-based halometallates, enabling one-step-deposition suitable for roll-to-roll process. This leads to higher degree of ligand exchange, sharper bandtail, lower trap density, and resultantly higher V OC in devices compared to conventional SSLE. We also first demonstrate that the photovoltaic performance can be improved by introducing ethanedithiol-exchanged AgBiS 2 NCs on SPLE-prepared AgBiS 2 NC solids because of favorable band alignment and extended depletion width. Thus, this enables improving device performance up to a power conversion efficiency of 4.08% with the highest V OC of 0.55 V among the AgBiS 2 NC photovoltaics reported so far.