Quantum Dot Light-Emitting Diodes with High Color Purity

We are proceeding with research on the development of displays with vibrant colors using environmentally friendly materials. We have developed vibrant red, green, and blue light-emitting diodes using a light-emitting material called quantum dots.

We have achieved high color purity luminescence through improvements to the material and light-emitting diode structure using quantum dots that do not include toxic elements such as cadmium or lead. This makes it possible to reproduce around 80% of the color range defined by the Rec. ITU-R BT.2020 international standard for 4K/8K. We are working on improving the color purity and light-emitting efficiency even further.

Quantum dot materials are small particle-shaped semiconductor crystals. Their structure, as illustrated above, is composed of a ligand for coloring using and ink solution around a core and shell, which are responsible for the luminescence. The core diameter is small, and ranges from ca. 1 to 10 nanometers*. One feature of quantum dot materials is that the color of the emitted light varies depending on the size of the core, changing to red as the size becomes larger, and to green and blue as the size becomes smaller. If the sizes of the particles are kept the same for each color, luminescence of vibrant colors with high color purity can be obtained.

* one nanometer is one millionth of a millimeter

Quantum dot light-emitting diodes are devices that consist of a thin film of quantum dot material sandwiched between two electrodes. The quantum dot material emits light when a current is passed through the electrodes. In the present work, we developed red, green, and blue quantum dot light-emitting diodes. Furthermore, we improved the light-emitting efficiency using an ink containing a mixture of quantum dot material and compatible materials.

Displays that can reproduce vibrant colors can be created using quantum dot light-emitting diodes. Furthermore, since quantum dot materials can be painted on like ink, in the future it may be possible to use them in flexible displays that can be carried around, or in large-scale displays that can be fixed to a surface like wallpaper.