Hybrid dual-stage flow-synthesis of eco-friendly ZnCuInSSe quantum dots for solar cells: Improvement in efficiency using inorganic ligand exchange

The large-scale synthesis of non-toxic, efficient quantum dots (QDs) is critical for expanding the practical application scope of QD-based photovoltaic (PV) devices. In this study, we synthesize ZnCuInSSe (ZCISSe) QDs on a gram scale (3.5 g) using a hybrid flow reactor method. This method is capable of producing QDs in gram quantities using solid-state chemicals. Additionally, by observing the composition, composition ratio, and reaction temperature, it is possible to produce ZCISSe QDs with highly controllable stoichiometry and a tuneable bandgap. Moreover, to improve the surface conditions of ZCISSe QDs, we propose for the first time the use of different types of surfactants with oleylamine (OAm) and S2− surface ligands via ligand-exchange techniques. Subsequently, we validate the PV quality of the manufactured ZCISSe QDs. Additionally, we develop QD-based solar cells, in which the TiO2 film functions as an n-type semiconductor. The S2--ligand-capped QD solar cell has a 25% higher power conversion efficiency than the OAm-ligand-capped QD solar cell.