Bright and Stable Quantum Dot Structures and Their Application to Display

Abstract

The synthetic methods to prepare high quality quantum dots (QDs) in the colloidal phase have been developed, and it has been proposed that the advantages of the QDs can be practically realized in various optoelectronic devices in the near future. In particular, red light emitting CdSe-based QDs have been significantly optimized in terms of the emission wavelengths, quantum efficiency, and the tolerance against fabrication conditions such as high temperature curing or chemical treatments. However, QE and stability diminish rapidly as the size of QDs are reduced, because the density of the surface defects are more easily generated by the large ratio of surface to volume and the steric hindrance of capping ligands. Here, we present the novel structure of QD consisting of the alloy core and multi shells (AC/MS) of which the emission could be tuned especially in green region (502 nm ~ 563 nm). For the alloy core, the previously reported CdSe//ZnS interfused gradient alloy structure was used as a blue core (PL=458 nm). And, additional crystalline layer was grown on the surface of the blue light emitting alloy core to build CdSZnS multi shells. Since the CdS has smaller energy band gap than the alloy core and excitons can be delocalized all over the CdSe//ZnS/CdS crystalline structure, the emission of the CdSe//ZnS/CdSZnS QDs shifts to lower energy depending on the thickness of the CdS layer. The CdSe//ZnS/CdSZnS AC/MS QDs showed 100% of quantum efficiency and narrow spectrum width. The AC/MS QDs also have strong stability against intense radiation and thermal process so that they showed 70 % of external quantum efficiency as a green color converter on a blue light emitting diode. A white LED made with optimized red and green QDs showed high efficacy of 45lm/W and about 96 % of color reproducibility compared to the NTSC color space.