Boosting Open-Circuit Voltage of AgBiS₂ Quantum Dot Solar Cells through Post-treatment Passivation

Silver bismuth disulfide (AgBiS2) colloidal quantum dots (CQDs) have emerged as attractive absorbers in ecofriendly photovoltaics due to their high absorption coefficient and suitable bandgap. However, it is a significant challenge to completely eliminate the numerous defect states on the entire surface of CQDs formed in solid-state ligand exchange. Here, we propose a simple stepwise passivation approach in which AgBiS2 CQD films are subjected to halide post-treatment after conventional surface passivation with iodide. This approach can compensate for the ligand loss on the surface of AgBiS2-CQD under a protic solvent attack. It not only largely reduces the surface trap density but also enhances the dielectric-screening effect, effectively promoting charge transport. Through gradual passivation with chloride ions and optimizing the thickness of the light-absorber layer, AgBiS2-CQD-based solar cells achieved a power conversion efficiency of 10.02% with a high open-circuit voltage of 0.581 V, which is among the highest reported values for this type of photovoltaic to date.