Inorganic metal iodide mediated solution phase surface passivation for quantum dot solar cell

The recent advancements in solution phase surface passivation of quantum dots (QDs) enable the development of production compatible QD ink for their large-area deposition, of a single coating. Surface passivation and colloidal stability of the QDs in polar solvents have been achieved using inorganic-organic hybrid halometallate ligands. The inorganic halometallate anions bind to the unsaturated metal sites of the QD surface, while the organic counter cations provide the colloidal stability and charge balance to the QDs. Organic ligands is a reason for concern though for the stability of the QD solar cells processed from solution-phase ligand exchange. Here, we report a solution-phase ligand exchange strategy using alkali metal halides as a substitution for the organic counterpart to facilitate solution-phase ligand exchange using all-inorganic halometallate ligands. Considering the limited solubility of the alkali halides in organic solvents a two-stage ligand-exchanged process has been commenced to help remove the excess ligands, preserve the electronic purity and allow the formation of highly passivated QD films from solution-phase deposition. A twofold increase in solar cell performance is shown with the help of the modified ligand exchange approach. The solar cell properties are further analysed through detailed characterizations of the QD solar cells.