Cascaded light emitting devices based on mixed conductor electroluminescence

• US 20060214570A1
• Filed: 03/28/2005
• Published: 09/28/2006
• Est. Priority Date: 03/28/2005
• Status: Active Grant

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University), Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University), Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Abruna, Hector D., Mori, Kiyotaka, Bernards, Daniel A., Slinker, Jason D., Malliaras, George M.
• Granted Patent: US 7,755,275 B2
• Time in Patent Office: Days
• US Class Current: 313/506
• CPC Class Codes: H10K 50/135 comprising mobile ions
• CPC Class Codes: H10K 50/19 Tandem OLEDs
• CPC Class Codes: H10K 50/805 Electrodes
• CPC Class Codes: H10K 50/856 comprising reflective means
• CPC Class Codes: H10K 59/32 Stacked devices having two or more layers, each emitting at different wavelengths
• CPC Class Codes: H10K 59/805 Electrodes
• CPC Class Codes: H10K 59/878 comprising reflective means
• CPC Class Codes: H10K 71/841 Applying alternating current [AC] during manufacturing or treatment

Abstract

A cascaded light emitting device. The cascaded light emitting device includes: a base electrode formed of a base electrode material and electrically coupled to a base voltage lead; a top electrode layer formed of a top electrode material and electrically coupled to a top voltage lead; a number of electroluminescent layers arranged between and electrically coupled to the base electrode and top electrode layer; and at least one middle electrode layer formed of a middle electrode material. Each of the middle electrodes is coupled between two juxtaposed electroluminescent layers. The electroluminescent layers include a mixed conductor that luminesces with a peak wavelength.

Claims

1. A cascaded light emitting device, comprising:

a base electrode formed of a base electrode material and electrically coupled to a base voltage lead;

a top electrode layer formed of a top electrode material and electrically coupled to a top voltage lead;

a plurality of electroluminescent layers arranged between and electrically coupled to the base electrode and top electrode layer, the plurality of electroluminescent layers including an mixed conductor that luminesces with a peak wavelength; and

at least one middle electrode layer formed of a middle electrode material, each middle electrode coupled between two juxtaposed electroluminescent layers of the plurality of electroluminescent layers.

2. The cascaded light emitting device according to claim 1, wherein:

at least one of the base electrode material or the top electrode material is substantially transmissive to light having the peak wavelength; and

the middle electrode material is substantially transmissive to light having the peak wavelength.

3. The cascaded light emitting device according to claim 1, wherein the base electrode is formed on a substrate formed of a substrate material that is substantially electrically insulating.

4. The cascaded light emitting device according to claim 1, wherein the base electrode material, the middle electrode material, and the substrate material are substantially transmissive to light having the peak wavelength.

5. The cascaded light emitting device according to claim 1, wherein the base electrode forms a substrate of the cascaded light emitting device.

6. The cascaded light emitting device according to claim 1, wherein:

one of the base electrode material or the top electrode material is substantially transmissive to light having the peak wavelength;

another one of the base electrode material or the top electrode material is substantially reflective to light having the peak wavelength; and

the middle electrode material is substantially transmissive to light having the peak wavelength.

7. The cascaded light emitting device according to claim 1, wherein:

the base electrode material includes at least one of a metal conductor, a metal alloy conductor, an oxide conductor, a ceramic conductor, a carbon-based conductor, a polymer conductor, an electrolyte, an ionic conductor, or a composite material formed of a conductor in a non-conducting matrix;

the top electrode material includes at least one of a metal conductor, a metal alloy conductor, an oxide conductor, a ceramic conductor, a carbon-based conductor, a polymer conductor, an electrolyte, an ionic conductor, or a composite material formed of a conductor in a non-conducting matrix; and

the middle electrode material includes at least one of a metal conductor, a metal alloy conductor, an oxide conductor, a ceramic conductor, a carbon-based conductor, a polymer conductor, an electrolyte, an ionic conductor, or a composite material formed of a conductor in a non-conducting matrix.

8. The cascaded light emitting device according to claim 1, wherein:

the plurality of electroluminescent layers include a first subset of electroluminescent layers and a second subset of electroluminescent layers, the first subset of electroluminescent layers including the mixed conductor that luminesces with the peak wavelength, and the second subset of electroluminescent layers including another mixed conductor that luminesces with another peak wavelength.

9. The cascaded light emitting device according to claim 8, wherein:

the plurality of electroluminescent layers further includes a third subset of electroluminescent layers, the third subset of electroluminescent layers including the further mixed conductor that luminesces with a further peak wavelength;

the peak wavelength at which the mixed conductor luminesces is a red visible wavelength, the other peak wavelength at which the other mixed conductor luminesces is a green visible wavelength, and the further peak wavelength at which the further mixed conductor luminesces is a blue visible wavelength;

the at least one middle electrode layer includes at least two middle layers coupled between juxtaposed electroluminescent layers from two different subsets of the plurality of electroluminescent layers; and

the middle electrode material and at least one of the base electrode material or the top electrode material is substantially transmissive to visible light.

10. The cascaded light emitting device according to claim 9, wherein each of the two middle layers coupled between juxtaposed electroluminescent layers from two different subsets of the plurality of electroluminescent layers is electrically coupled to a respective color control voltage lead.

11. The cascaded light emitting device according to claim 1, wherein the mixed conductor is at least one of a transition metal complex or an ionic liquid.

12. The cascaded light emitting device according to claim 1, wherein the at least one middle electrode layer includes at least two middle electrodes coupled between different portions of a pair of juxtaposed electroluminescent layers.

13. The cascaded light emitting device according to claim 1, wherein the at least one middle electrode layer includes a middle electrode coupled between a pair of juxtaposed electroluminescent layers such that the pair of juxtaposed electroluminescent layers are physically separated by the middle electrode.

14. The cascaded light emitting device according to claim 1, wherein the at least one middle electrode layer includes a middle electrode electrically coupled to a middle voltage lead.

15. The cascaded light emitting device according to claim 1, further comprising a cover layer formed of a cover material that is substantially electrically insulating and coupled to the top electrode.

16. A cascaded light emitting device, comprising:

a split electrode structure formed of a first electrode material, the split electrode structure includes a plurality of electrode portions, an electrical resistance between any pair of electrode portions of the split electrode structure being greater than a split resistance, the plurality of electrode portions including a first electrode portion electrically coupled to a first voltage lead and a second electrode portion electrically coupled to a second voltage lead;

an opposing electrode formed of a second electrode material; and

at least one electroluminescent layer coupled between the split electrode structure and the opposing electrode, the at least one electroluminescent layer including a mixed conductor that luminesces with a peak wavelength, a total thickness of the at least one electroluminescent layer being such that a resistance across the at least one electroluminescent layer between an electrode portion of the split electrode structure and the opposing electrode is less than half of the split resistance.

17. The cascaded light emitting device according to claim 16, wherein at least one of the first electrode material or the second electrode material is substantially transmissive to light having the peak wavelength.

18. The cascaded light emitting device according to claim 16, wherein one of the split electrode structure or the opposing electrode is formed on a substrate formed of a substrate material that is substantially electrically insulating.

19. The cascaded light emitting device according to claim 17, wherein the one of the split electrode structure or the opposing electrode formed on the substrate and the substrate material are substantially transmissive to light having the peak wavelength.

20. The cascaded light emitting device according to claim 17, wherein the substrate material is substantially reflective to light having the peak wavelength.

21. The cascaded light emitting device according to claim 17, wherein a cover layer formed of a cover material that is substantially electrically insulating is coupled to one of the split electrode structure or the opposing electrode not formed on the substrate.

22. The cascaded light emitting device according to claim 16, wherein the opposing electrode forms a substrate of the cascaded light emitting device.

23. The cascaded light emitting device according to claim 16, wherein:

one of the first electrode material or the second electrode material is substantially transmissive to light having the peak wavelength; and

another one of the first electrode material or the second electrode material is substantially reflective to light having the peak wavelength

24. The cascaded light emitting device according to claim 16, wherein:

the first electrode material includes at least one of a metal conductor, a metal alloy conductor, an oxide conductor, a ceramic conductor, a carbon-based conductor, a polymer conductor, an electrolyte, an ionic conductor, or a composite material formed of a conductor in a non-conducting matrix; and

the second electrode material includes at least one of a metal conductor, a metal alloy conductor, an oxide conductor, a ceramic conductor, a carbon-based conductor, a polymer conductor, an electrolyte, an ionic conductor, or a composite material formed of a conductor in a non-conducting matrix.

25. The cascaded light emitting device according to claim 16, wherein the opposing electrode is sized and arranged such that a section of the opposing electrode extends across each separation between the plurality of electrode portions of the split electrode structure.

26. The cascaded light emitting device according to claim 25, wherein the opposing electrode includes a plurality of opposing electrode portions, each opposing electrode portion being:

sized and arranged to extend across a separation between two of the plurality of electrode portions of the split electrode structure; and

separated from other opposing electrode portions by at least the split distance.

27. The cascaded light emitting device according to claim 16, wherein the opposing electrode is electrically coupled to at least one opposing voltage lead.

28. The cascaded light emitting device according to claim 16, wherein the mixed conductor is at least one of a transition metal complex or an ionic liquid.

29. The cascaded light emitting device according to claim 16, further comprising:

at least one middle electrode layer formed of a middle electrode material;

wherein;

the at least one electroluminescent layer is a plurality of electroluminescent layers; and

each middle electrode layer is coupled between two juxtaposed electroluminescent layers of the plurality of electroluminescent layers.

30. The cascaded light emitting device according to claim 29, wherein the middle electrode material includes at least one of a metal conductor, a metal alloy conductor, an oxide conductor, a ceramic conductor, a carbon-based conductor, a polymer conductor, an electrolyte, an ionic conductor, or a composite material formed of a conductor in a non-conducting matrix.

31. The cascaded light emitting device according to claim 29, wherein the at least one middle electrode layer includes a plurality of middle electrode portions.

32. The cascaded light emitting device according to claim 31, wherein the at least one middle electrode layer includes a middle electrode portion electrically coupled to a middle voltage lead.

33. The cascaded light emitting device according to claim 29, wherein each middle electrode layer includes at least one middle electrode portion that is sized and arranged to:

extend across a separation between two of the plurality of electrode portions of the split electrode structure;

or

substantially overlay one of the plurality of electrode portions of the split electrode structure.

34. A method for driving of an electroluminescent device with an alternating current, the electroluminescent device including a first electrode, a second electrode, and at least one electroluminescent layer coupled between the first electrode and the second electrode, the at least one electroluminescent layer including an mixed conductor, the method comprising the steps of:

a) biasing the electroluminescent device to generate a polarizing voltage across the at least one electroluminescent layer from the first electrode to the second electrode, the polarization voltage being greater than or equal to a voltage necessary to enhance charge injection into the mixed conductor;

b) maintaining a potential difference across the at least one electroluminescent layer from the first electrode to the second electrode above an operational voltage for a predetermined luminescence period, the operational voltage being less than or equal to the polarizing voltage and greater than or equal to a voltage necessary to drive electroluminescence in the polarized mixed conductor;

c) biasing the electroluminescent device to generate the polarizing voltage across the at least one electroluminescent layer from the second electrode to the first electrode;

d) maintaining the potential difference across the at least one electroluminescent layer from the second electrode to the first electrode above an operational voltage for the predetermined luminescence period; and

e) repeating steps (a), (b), (c), (d), and (e).

35. The method according to claim 34, wherein the alternating current driving method using one of a sinusoidal driving signal, a triangle wave driving signal, sawtooth driving signal, a square wave driving signal, a rectangular wave driving signal, a tangent wave driving signal, a trapezoidal wave driving signal, or a spiked square wave driving signal.

36. A method for rectifying an input electric signal having a varying voltage, the method comprising the steps of:

a) driving an electroluminescent device that includes an mixed conductor with the electric signal to generate an optical signal having an intensity proportional to an absolute value of the varying voltage of the electric signal; and

b) detecting the optical signal of the electroluminescent device to generate a rectified electric signal.

37. The method according to claim 36, wherein step (a) includes adding a DC bias voltage to the electric signal such that a range of the varying voltage is centered on about zero volts.

38. The method according to claim 37, wherein:

the electric signal is periodic and has a peak frequency; and

step (b) includes generating a periodic rectified electric signal having a rectified peak frequency equal to twice the peak frequency of the electric signal.