EL element and method for manufacturing EL element with a light-emitting layer including an ionic liquid, a phosphorescent material, and a fluorescent material

Patent metadata

Field	Value
Publication number	US-10693096-B2
Application number	US-201716082995-A
Country	US
Kind code	B2
Filing date	Mar 16, 2017
Priority date	Mar 18, 2016
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

Abstract

Provided is an EL element utilizing upconversion light emission involving highly efficient triplet-triplet annihilation. A blue-light-emitting layer includes an ionic liquid, a red phosphorescent material, and a blue fluorescent material. The blue fluorescent material and the red phosphorescent material are homogeneously dispersed in a liquid film of the ionic liquid.

First claim

The invention claimed is:

1. An EL element comprising:
a red-light-emitting region, a green-light-emitting region, and a blue-light-emitting region;
a first electrode and a second electrode that are in each of the red-light-emitting region, the green-light-emitting region, and the blue-light-emitting region;
EL layers provided between the first electrode and the second electrode in each of the red-light-emitting region, the green-light-emitting region, and the blue-light-emitting region;
a light-emitting layer included in each of the EL layers; and
a bank including portions provided between adjacent pairs of the light-emitting layers, wherein
the EL layers include a red-light-emitting EL layer, a green-light-emitting EL layer, and a blue-light-emitting EL layer,
distances between an upper surface of the red-light-emitting EL layer and an upper surface of the bank, between an upper surface of the green-light-emitting EL layer and the upper surface of the bank, and between an upper surface of the blue-light-emitting EL layer and the upper surface of the bank are respectively arranged in descending order of length,
each of the light-emitting layers includes an ionic liquid, a phosphorescent material, and a fluorescent material,
a lowest triplet excited state energy level of the phosphorescent material is higher than a lowest triplet excited state energy level of the fluorescent material, and a lowest singlet excited state energy level of the fluorescent material is higher than a lowest singlet excited state energy level of the phosphorescent material, and
the fluorescent material and the phosphorescent material are homogeneously dispersed in a liquid film of the ionic liquid.

2. The EL element according to claim 1 , wherein a fluorescence wavelength of the fluorescent material is in an ultraviolet range or a blue wavelength range.

3. The EL element according to claim 1 , wherein
a reflective electrode is provided to a surface of the first electrode, the surface being opposite to the light-emitting layer,
the first electrode is a transparent electrode or a semitransparent electrode, and
a distance between the reflective electrode and the second electrode is a distance forming an optical path length that is in accordance with a fluorescence wavelength of the fluorescent material.

4. The EL element according to claim 1 , wherein
a reflective electrode is provided to a surface of the first electrode, the surface being opposite to the light-emitting layer,
the second electrode is a transparent electrode or a semitransparent electrode, and
a distance between the reflective electrode and the second electrode is a distance forming an optical path length that is in accordance with a fluorescence wavelength of the fluorescent material.

5. The EL element according to claim 1 , wherein
each of the light-emitting layers includes a first light-emitting layer and a second light-emitting layer, the first light-emitting layer and the second light-emitting layer being layered between the first electrode and the second electrode,
the first light-emitting layer includes the phosphorescent material and a first fluorescent material, and
the second light-emitting layer includes the phosphorescent material and a second fluorescent material having a fluorescence wavelength different from a fluorescence wavelength of the first fluorescent material.

6. The EL element according to claim 5 , wherein a partition layer is provided between the first light-emitting layer and the second light-emitting layer, the partition layer being configured to suppress energy exchange between a material included in the first light-emitting layer and a material included in the second light-emitting layer.

7. The EL element according to claim 1 , wherein an intermolecular distance of the fluorescent material in the light-emitting layer is from 0 nm to 1 nm.

8. The EL element according to claim 1 , wherein an intermolecular distance of the phosphorescent material in the light-emitting layer is greater than 10 nm and 40 nm or less.

9. The EL element according to claim 1 , wherein the ionic liquid is hydrophobic.

10. The EL element according to claim 1 , wherein the ionic liquid is configured to produce a cation-n interaction between the fluorescent material and the phosphorescent material.

11. The EL element according to claim 1 , wherein the ionic liquid has a viscosity at 300K from 0.000001 PaS to 1 PaS.

12. The EL element according to claim 1 , wherein a melting point and a freezing point of the ionic liquid are each from −200° C. to 0° C.

13. A method for manufacturing an EL element, the EL element including:
a red-light-emitting region, a green-light-emitting region, and a blue-light-emitting region;
a first electrode and a second electrode that are in each of the red-light-emitting region, the green-light-emitting region, and the blue-light-emitting region;
EL layers provided between the first electrode and the second electrode in each of the red-light-emitting region, the green-light-emitting region, and the blue-light-emitting region; and
a light-emitting layer included in each of the EL layers, the EL layers including a red-light-emitting EL layer, a green-light-emitting EL layer, and a blue-light-emitting EL layer, wherein
each of the light-emitting layers includes a phosphorescent material and a fluorescent material, a lowest triplet excited state energy level of the phosphorescent material is higher than a lowest triplet excited state energy level of the fluorescent material, and a lowest singlet excited state energy level of the fluorescent material is higher than a lowest singlet excited state energy level of the phosphorescent material, the method comprising:
forming a bank to define each of the red-light-emitting region, the green-light-emitting region, and the blue-light-emitting region; and
forming each of the light-emitting layers by codepositing an ionic liquid, the phosphorescent material, and the fluorescent material into respective ones of the red-light-emitting region, the green-light-emitting region, and the blue-light-emitting region, wherein
distances between an upper surface of the red-light-emitting EL layer and an upper surface of the bank, between an upper surface of the green-light-emitting EL layer and the upper surface of the bank, and between an upper surface of the blue-light-emitting EL layer and the upper surface of the bank are respectively arranged in descending order of length.

14. The method for manufacturing an EL element, according to claim 13 , wherein the ionic liquid, the phosphorescent material, and the fluorescent material are codeposited in a vacuum.

Assignees

• Sharp Kk

Inventors

• ITO Asae
• Niboshi Manabu
• Tsukamoto Yuto
• Kawato Shinichi

Classifications

• H10K50/11

  characterised by the electroluminescent [EL] layers · CPC title

• H10K50/135 Primary

  comprising mobile ions · CPC title

• H10K2101/10

  Triplet emission · CPC title

• H10K71/164

  using vacuum deposition · CPC title

• H10K2101/27

  Combination of fluorescent and phosphorescent emission · CPC title