Simultaneous ligand and cation exchange in PbSe/CdSe nanocrystal films

Abstract

Trap states formed at the surface of colloidal semiconductor nanocrystals can have deleterious impact on performance in emerging optoelectronic applications. To mitigate surface traps in nanocrystal thin films we investigated simultaneous surface passivation and ligand exchange for PbSe nanocrystal films via treatment with a cadmium acetate solution. We show that a kinetically limited surface cation exchange produces a thin CdxPb1−xSe shell that effectively passivates the nanocrystal surface as confirmed by increased photoluminescence intensity and photoluminescence lifetime. Ligand exchange to acetate ligands is confirmed via Fourier transform infrared spectroscopy and grazing incidence small angle X-ray scattering. We studied the impact of the cadmium acetate treatment on interparticle coupling and found that the reduced interparticle spacing and limited shell thickness leads to increased Förster resonant energy transfer in nanocrystal films. Simultaneous cation/ligand exchange enables the production of heterostructured nanocrystal films with properties like Quasi-Type II nanocrystals synthesized in solution.