Light emitting device

• US 7,535,440 B2
• Filed: 04/04/2003
• Issued: 05/19/2009
• Est. Priority Date: 04/09/2002
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Nishi, Takeshi, Shibata, Noriko
• Primary Examiner(s): Liang; Regina
• Application Number:
  US10/406,598
• Publication Number:
  US 20030218173A1
• Time in Patent Office: 2,237 Days
• Field of Search: 345 76- 79, 345 82- 83, 315/169.3, 313/506, 313/504
• US Class Current: 345/76
• CPC Class Codes: H10K 2102/3026 Top emission
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/122 Pixel-defining structures or layers, e.g. banks
• CPC Class Codes: H10K 59/17 Passive-matrix OLED displays
• CPC Class Codes: H10K 59/173 comprising banks or shadow masks
• CPC Class Codes: H10K 59/32 Stacked devices having two or more layers, each emitting at different wavelengths
• CPC Class Codes: H10K 71/841 Applying alternating current [AC] during manufacturing or treatment

Abstract

A light emitting element, in which voltages having different polarities are applied alternately in order to prevent the accumulation of electric charge in an organic compound layer of the light emitting element, and in which light is always emitted, no matter whether a positive polarity voltage or a negative polarity voltage is applied, is provided. An opposing electrode is formed between a first electrode and a second electrode, and a first light emitting element having a compound layer that contains a first organic substance between the first electrode and the opposing electrode, and a second light emitting element having a compound layer that contains a second organic substance between the opposing electrode and the second electrode, are formed in the present invention. Note that a constant voltage (reference voltage) is imparted to the opposing electrode, and that voltages having inverse polarities are applied simultaneously, and alternately for fixed periods of time, to the first electrode and the second electrode. A light emitting element that always emits light, even if the polarity of the applied voltage changes, can thus be formed.

Claims

1. A light emitting device comprising:

a first electrode;

a first chemical compound layer containing a first organic substance;

an opposing electrode;

a second chemical compound layer containing a second organic substance; and

a second electrode,

wherein the first chemical compound layer is disposed between the first electrode and the opposing electrode, and the second chemical compound layer is disposed between the opposing electrode and the second electrode;

wherein a fixed voltage is applied to the opposing electrode; and

wherein one of the first chemical compound layer and the second chemical compound layer emits light alternately for fixed periods by applying a voltage having one of a positive polarity and a negative polarity taking the fixed voltage as a reference alternately for the fixed periods to the first electrode and simultaneously applying a voltage which is inverse in polarity to the voltage applied to the first electrode taking the fixed voltage as a reference to the second electrode.

2. A light emitting device according to claim 1, wherein one of the first electrode and the second electrode is formed by using a light transmitting conductive material.

3. A light emitting device according to claim 1, wherein the opposing electrode has a structure in which films made from a plurality of materials are laminated.

4. A light emitting device according to claim 1, wherein the opposing electrode has a laminate structure in which a light transmitting conductive film is sandwiched between films made from a material having a work function which is equal to or less than 3.8 eV.

5. A light emitting device according to claim 1, wherein the light emitting device composes one selected from the group consisting of a digital still camera, a laptop type personal computer, a DVD reproduction apparatus, a goggle type display and a cellular phone.

6. A light emitting device comprising:

a first electrode;

a first chemical compound layer containing a first organic substance;

an opposing electrode;

a second chemical compound layer containing a second organic substance; and

a second electrode,

wherein the first chemical compound layer is disposed between the first electrode and the opposing electrode, and the second chemical compound layer is disposed between the opposing electrode and the second electrode;

wherein a fixed voltage is applied to the opposing electrode; and

wherein by applying a voltage having one of a positive polarity and a negative polarity taking the fixed voltage as a reference alternately for fixed periods to the first electrode and simultaneously applying a voltage which is inverse in polarity to the voltage applied to the first electrode taking the fixed voltage as a reference to the second electrode,

a forward bias is applied to one of the first chemical compound layer and the second chemical compound layer, and simultaneously a reverse bias is applied to the other one of the first chemical compound layer and the second chemical compound layer; and

polarities of the biases applied to the first chemical compound layer and the second chemical compound layer are changed alternately for the fixed periods.

7. A light emitting device according to claim 6, wherein one of the first electrode and the second electrode is formed by using a light transmitting conductive material.

8. A light emitting device according to claim 6, wherein the opposing electrode has a structure in which films made from a plurality of materials are laminated.

9. A light emitting device according to claim 6, wherein the opposing electrode has a laminate structure in which a light transmitting conductive film is sandwiched between films made from a material having a work function which is equal to or less than 3.8 eV.

10. A light emitting device according to claim 6, wherein the light emitting device composes one selected from the group consisting of a digital still camera, a laptop type personal computer, a DVD reproduction apparatus, a goggle type display and a cellular phone.

11. A light emitting device comprising:

a first anode electrode;

a first chemical compound layer containing a first organic substance;

a cathode electrode;

a second chemical compound layer containing a second organic substance; and

a second anode electrode,

wherein the first chemical compound layer is disposed between the first anode electrode and the cathode electrode, and the second chemical compound layer is disposed between the cathode electrode and the second anode electrode;

wherein the first anode electrode and the second anode electrode are formed by an anodic material and the cathode electrode is formed by a cathodic material;

wherein a fixed voltage is applied to the cathode electrode; and

wherein the first chemical compound layer emits light by applying a voltage having a positive polarity taking the fixed voltage as a reference to the first anode electrode, and electric charge accumulated in the second chemical compound layer is simultaneously relieved by applying a voltage having a negative polarity taking the fixed voltage as a reference to the second anode electrode.

12. A light emitting device according to claim 11, wherein one of the first anode electrode and the second anode electrode is formed by using a light transmitting conductive material.

13. A light emitting device according to claim 11, wherein the cathode electrode has a structure in which films made from a plurality of materials are laminated.

14. A light emitting device according to claim 11, wherein the cathode electrode has a laminate structure in which a light transmitting conductive film is sandwiched between films made from a material having a work function which is equal to or less than 3.8 eV.

15. A light emitting device according to claim 11, wherein the light emitting device composes one selected from the group consisting of a digital still camera, a laptop type personal computer, a DVD reproduction apparatus, a goggle type display and a cellular phone.

16. A light emitting device comprising:

a first electrode;

a first chemical compound layer containing a first organic substance;

an opposing electrode;

a second chemical compound layer containing a second organic substance; and

a second electrode,

wherein the first chemical compound layer is disposed between the first electrode and the electrode, and the second chemical compound layer is disposed between the electrode and the second electrode;

wherein the first electrode and the second electrode are formed by an anodic material and the opposing electrode is formed by a cathodic material;

wherein a fixed voltage is applied to the opposing electrode;

wherein by applying a voltage having one of the positive polarity and the negative polarity taking the voltage applied to the opposing electrode as a reference alternately for fixed periods to the first electrode, and simultaneously applying a voltage, which is inverse in polarity to the voltage applied to the first electrode taking the voltage applied to the opposing electrode as a reference, alternately for the fixed periods to the second electrode;

the first chemical compound layer emits light during applying the positive polarity voltage to the first electrode; and

the second chemical compound layer emits light during applying the positive polarity voltage to the second electrode.

17. A light emitting device according to claim 16, wherein one of the first electrode and the second electrode is formed by using a light transmitting conductive material.

18. A light emitting device according to claim 16, wherein the opposing electrode has a structure in which films made from a plurality of materials are laminated.

19. A light emitting device according to claim 16, wherein the opposing electrode has a laminate structure in which a light transmitting conductive film is sandwiched between films made from a material having a work function which is equal to or less than 3.8 eV.

20. A light emitting device according to claim 16, wherein the light emitting device composes one selected from the group consisting of a digital still camera, a laptop type personal computer, a DVD reproduction apparatus, a goggle type display and a cellular phone.

21. A light emitting device comprising:

a first anode electrode;

a first chemical compound layer containing a first organic substance;

a cathode electrode;

a second chemical compound layer containing a second organic substance; and

a second anode electrode,

wherein the first chemical compound layer is disposed between the first anode electrode and the cathode electrode, and the second chemical compound layer is disposed between the cathode electrode and the second anode electrode;

wherein a fixed voltage is applied to the cathode electrode;

wherein a voltage having one of a positive polarity and a negative polarity taking the fixed voltage as a reference is alternately for fixed periods applied to the first anode electrode and simultaneously a voltage which is inverse in polarity to the voltage applied to the first anode electrode taking the fixed voltage as a reference is applied to the second anode electrode,

wherein the first chemical compound layer emits light by applying a voltage having the positive polarity taking the fixed voltage as a reference to the first anode electrode, and electric charge accumulated in the second chemical compound layer is simultaneously relieved by applying a voltage having the negative polarity taking the fixed voltage as a reference to the second anode electrode.

22. A light emitting device according to claim 21, wherein one of the first anode electrode and the second anode electrode is formed by using a light transmitting conductive material.

23. A light emitting device according to claim 21, wherein the cathode electrode has a structure in which films made from a plurality of materials are laminated.

24. A light emitting device according to claim 21, wherein the cathode electrode has a laminate structure in which a light transmitting conductive film is sandwiched between films made from a material having a work function which is equal to or less than 3.8 eV.

25. A light emitting device according to claim 21, wherein the light emitting device composes one selected from the group consisting of a digital still camera, a laptop type personal computer, a DVD reproduction apparatus, a goggle type display and a cellular phone.