Giant Photoconductivity of Annealed CdSe/CdS Nanoplatelet Films

In this paper, we experimentally investigate the effect of annealing and ligand removal on the electrical and photovoltaic properties of polycrystalline films formed from a colloidal solution of heterostructured CdSe/CdS nanoparticles in chlorobenzene using the drop-casting method. Annealing leads to a significant increase in photoconductivity, up to 4 orders of magnitude, while the band gap of the CdSe/CdS nanoplatelet film remains unchanged. Moreover, it was shown that the annealing causes a change in the dominant recombination mechanism from monomolecular to bimolecular due to an increase in charge carrier mobility. These findings directly demonstrate the possibility of creating highly photoconductive nanocrystalline films with tunable optical and electrical properties. Moreover, annealing also provides the growth of photosensitivity from approximately 0.87 to 2.75 A/W for photons with 2.12 eV energy, which is a record value for such nanocrystalline films. Considered films have the potential to significantly enhance the sensitivity of photodetectors and solar cell efficiency.