Impact of surface ligands on the photocurrent enhancement due to multiple exciton generation in close-packed nanocrystal thin films

Semiconducting nanocrystal quantum dot (QD) films with high multiple exciton generation (MEG) efficiencies and high exciton dissociation efficiencies are appealing as solar cell materials. Here, we report the strong enhancement of the photocurrent in close-packed QD films, and discuss the importance of surface ligands on MEG and charge transport in QD films. Both exciton-recombination and charge-transport properties are influenced by the phenomenon of carrier tunnelling between neighboring QDs in thin films. These results can have important implications in the design of chemical treatments to control the electronic interactions between QDs in solution-processed solar cells. We demonstrate that the inorganic- and small sized-ligand passivation of PbS QDs by potassium thiocyanate causes a significant photocurrent enhancement.