Small-molecule engineering of a PbS QD/ZnO nanowire interface and its impact on infrared PbS QD solar cell performance

) functional groups were strategically selected to tune the interfacial energetics based on their molecular dipoles, their electron-withdrawing abilities, and the surface coverage on ZnO, among other factors. These molecular modifications revealed the key parameters that influenced the energy levels of the conduction band minimum, the valence band maximum, and the Fermi level, thereby shaping the overall band structure of the PbS QD/ZnO NW heterojunction. Controlled interface engineering enables the transformation of spike-shaped heterojunctions, which impede carrier transport from the PbS QD region to the ZnO region, into cliff-shaped junctions, which are more favourable for carrier extraction. Solar cells with cliff-shaped heterojunctions exhibit increased short-circuit current densities and external quantum efficiencies. Importantly, the carrier-recombination frequency at the interface depended significantly on the type of functional group introduced by the modifying molecules. This study provides valuable insights into the selection and design of modifying molecules for controlling the properties of metal oxide/infrared QD heterojunction-based solar cells.