Light Emitting Element and Light Emitting Device Using the Same

• US 20080241586A1
• Filed: 11/04/2005
• Published: 10/02/2008
• Est. Priority Date: 11/05/2004
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Seo, Satoshi, Kumaki, Daisuke
• Granted Patent: US 8,202,630 B2
• Time in Patent Office: Days
• US Class Current: 428/690
• CPC Class Codes: H10K 2102/351 Thickness
• CPC Class Codes: H10K 50/00 Organic light-emitting devices integrated devices or assemblies of multiple devices H10K59/00, H10K65/00; organic semiconductor lasers H01S5/36
• CPC Class Codes: H10K 50/17 Carrier injection layers
• CPC Class Codes: H10K 50/171 Electron injection layers
• CPC Class Codes: H10K 50/85 Arrangements for extracting light from the devices
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/17 Passive-matrix OLED displays
• CPC Class Codes: H10K 85/633 comprising polycyclic condensed aromatic hydrocarbons as substituents on the nitrogen atom
• CPC Class Codes: H10K 85/636 comprising heteroaromatic hydrocarbons as substituents on the nitrogen atom
• CPC Class Codes: Y10S 428/917 Electroluminescent

Abstract

An object of the prevent invention is to provide a light emitting element having slight increase in driving voltage with accumulation of light emitting time. Another object of the invention is to provide a light emitting element having slight increase in resistance with increase in film thickness. In an aspect of the invention, a light emitting element includes first, second and layers between mutually-facing first and second electrodes. The first layer is provided to be closer to the first electrode than the second layer. The third layer is provided to be closer to the second electrode than the second layer. The first layer contains a bipolar substance and a substance exhibiting an electron accepting ability with respect to the bipolar substance. The second layer contains a bipolar substance and a substance exhibiting an electron donating ability with respect to the bipolar substance. The third layer contains a light emitting substance.

Claims

1. A light emitting element comprising:

a first layer;

a second layer, and

a third layer,

wherein the first, second and third layers are interposed between mutually-facing first and second electrodes,

wherein the first layer contains a first substance of which a ratio of any one of an electron mobility and a hole mobility to the other one is 100 or less, and a second substance exhibiting an electron accepting ability with respect to the first substance,

wherein the second layer contains a third substance of which a ratio of any one of an electron mobility and a hole mobility to the other one is 100 or less, and a fourth substance exhibiting an electron donating ability with respect to the third substance,

wherein the third layer contains a light emitting substance,

wherein the first, second and third layers are sequentially laminated,

wherein the first layer is in contact with the first electrode,

wherein the third layer is in contact with the second electrode, and

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light.

3. The light emitting element according to claim 1 or claim 2, wherein the first layer contains the second substance such that a molar ratio of the second substance to the first substance is 0.5 or more and 2 or less.

11. A light emitting device, wherein a pixel portion includes the light emitting element according to any one of claim 1 through claim 10.

12. An electronic appliance, wherein a display portion includes the light emitting element according to claim 11.

2. A light emitting element comprising:

a first layer;

a second layer; and

a third layer,

wherein the first, second and third layers are interposed between mutually-facing first and second electrodes,

wherein the first layer contains a first substance of which a ratio of any one of an electron mobility and a hole mobility to the other one is 100 or less, and a second substance exhibiting an electron accepting ability with respect to the first substance,

wherein the second layer contains a third substance of which a ratio of any one of an electron mobility and a hole mobility to the other one is 100 or less, and a fourth substance exhibiting an electron donating ability with respect to the third substance,

wherein the third layer contains a light emitting substance,

wherein the first layer is provided to be closer to the first electrode than the second layer,

wherein the third layer is provided to be closer to the second electrode than the second layer, and

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light.

4. A light emitting element comprising:

a first layer,

a second layer; and

a third layer,

wherein the first, second and third layers are interposed between mutually-facing first and second electrodes,

wherein the first layer contains a first substance expressed by either a general formula 1 or a general formula 2, and a second substance exhibiting an electron accepting ability with respect to the first substance,

wherein the second layer contains a third substance expressed by either the general formula 1 or the general formula 2, and a fourth substance exhibiting an electron donating ability with respect to the third substance,

wherein the third layer contains a light emitting substance,

wherein the first, second and third layers are sequentially laminated,

wherein the first layer is in contact with the first electrode,

wherein the third layer is in contact with the second electrode, and

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light.

6. The light emitting element according to claim 4 or claim 5, wherein the first substance is identical to the third substance.

5. A light emitting element comprising:

a first layer;

a second layer; and

a third layer,

wherein the first, second and third layers are interposed between mutually-facing first and second electrodes,

wherein the first layer contains a first substance expressed by either a general formula 1 or a general formula 2, and a second substance exhibiting an electron accepting ability with respect to the first substance,

wherein the second layer contains a third substance expressed by either the general formula 1 or the general formula 2, and a fourth substance exhibiting an electron donating ability with respect to the third substance,

wherein the third layer contains a light emitting substance,

wherein the first layer is provided to be closer to the first electrode than the second layer,

wherein the third layer is provided to be closer to the second electrode than the second layer, and

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light.

7. A light emitting element comprising:

a first layer containing a first substance of which a ratio of any one of an electron mobility and a hole mobility to the other one is 100 or less; and

a second layer containing a light emitting substance,

wherein the first and second layers are interposed between mutually-facing first and second electrodes,

wherein the first layer includes a first region containing a second substance that exhibits an electron accepting ability with respect to the first substance, and a second region containing a third substance that exhibits an electron donating ability with respect to the first substance,

wherein the first region is provided to be closer to the first electrode than the second region, and

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light.

9. The light emitting element according to claim 7 or claim 8, wherein the first layer contains the second substance or the third substance such that a molar ratio of the second substance or the third substance to the first substance is 0.5 to 2.

8. A light emitting element comprising:

a first layer containing a first substance expressed by either a general formula 1 or a general formula 2; and

a second layer containing a light emitting substance,

wherein the first and second layers are interposed between mutually-facing first and second electrodes,

wherein the first layer includes a first region containing a second substance that exhibits an electron accepting ability with respect to the first substance, and a second region containing a third substance that exhibits an electron donating ability with respect to the first substance,

wherein the first region is provided to be closer to the first electrode than the second region, and

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light.

10. A light emitting element comprising:

a first layer;

a second layer; and

a third layer,

wherein the first, second and third layers are interposed between mutually-facing first and second electrodes,

wherein the first electrode is formed using a conductive material having a reflectance of 50% or more and 100% or less,

wherein the second electrode is formed using a conductive material that can transmit visible light,

wherein the first layer contains a first substance of which a ratio of any one of an electron mobility and a hole mobility to the other one is 100 or less, and a second substance exhibiting an electron accepting ability with respect to the first substance,

wherein the second layer contains a third substance of which any one of an electron mobility and a hole mobility to the other one is 100 or less, and a fourth substance exhibiting an electron donating ability with respect to the third substance,

wherein the third layer contains a light emitting layer and includes x pieces of layers (x is an arbitral positive integer),

wherein the first, second and third layers are sequentially laminated,

wherein the first layer is in contact with the first electrode,

wherein one layer included in the third layer is in contact with the second layer,

wherein the x-th layer included in the third layer is in contact with the second electrode,

wherein y pieces of layers (y<

x, y is a positive integer) are interposed between the light emitting layer and the second layer,

wherein when a voltage is applied to the light emitting element such that a potential of the second electrode is higher than that of the first electrode, the light emitting element emits light, and

wherein a thickness of the first layer and a thickness of the second layer are adjusted to satisfy an expression 1, an expression 2 and an expression 3;