The photoluminescence of CuInS2nanocrystals: effect of non-stoichiometry and surface modification

Abstract

Effects of large copper deficiency and surface modification on the photoluminescence of CuInS₂ nanocrystals were explored. The large copper deficiency improved PL intensity due to the enhanced internal defect-related emission. Surface modification of copper deficient nanocrystals by simply refluxing with zinc acetate and fatty acid resulted in more than 10 times improvement in the photoluminescence intensity and a large blueshift of the photoluminescence spectra. The uniformity in size/shape distribution after surface modification was attributed to the origin of shrinkage in Stokes shift from ∼600 meV to ∼300 meV in Cu_0.2InS₂/ZnS nanocrystals. Furthermore, the contribution of lattice strain to this large blueshift in emission wavelength in Cu_0.2InS₂/ZnS nanocrystals was proposed and tested with the CdS shell layers. The electronic process underlying the large enhancement of PL intensity was studied with time-resolved and temperature-dependent photoluminescence. This drastically enhanced photoluminescence after surface modification was attributed to the efficient reduction of non-radiative recombination originated from surface trap states, the activation energy of which was estimated to be 85 meV.