Improvement of electroluminescent characteristics in quantum dot light-emitting diodes using ZnInP/ZnSe/ZnS quantum dots by mixing an electron transport material into the light-emitting layer

Abstract

Quantum dots (QDs) are expected to be applied to emitting materials used in wide-color-gamut displays. However, the development of low-toxic alternatives is necessary because QDs that exhibit high color purity and highly efficient emission contain toxic materials such as Cd. In the present study, quantum dot light-emitting diodes (QD-LEDs) prepared using ZnInP/ZnSe/ZnS QDs as InP-based QDs were fabricated, and their electroluminescence (EL) properties were investigated. The synthesized QD dispersion showed a green photoluminescence (PL) spectrum with a peak wavelength of 509 nm, a full-width at half-maximum (FWHM) of 41 nm, and a PL quantum yield of 59.8%. Tris[2,4,6-trimethyl-3-(pyridin-3-yl)phenyl]borane (3TPYMB), which is an electron-transporting material (ETM), was added to the emitting layer (EML) of the QD-LEDs. The QDs and the ETM were nonuniformly deposited, the density of QDs in the EML was reduced, and the process of injecting electrons and holes into the QDs was changed. 3TPYMB assisted in recombination in the QDs because the electron injection barrier from 3TPYMB to the QDs was sufficiently small and because the deep highest occupied molecular orbital level effectively blocked holes. As a result, the external quantum efficiency was improved from 0.24% to 1.01%, and stable EL spectra with a peak wavelength of 522 nm and an FWHM of 46 nm, similar to the PL spectrum of the QD film, were obtained without being dependent on luminance. A bright and stable green EL emission was achieved with an InP-based QD-LED blended with 3TPYMB.