1. Chapter 4: Electroluminescence

2. ZnS
/Cu/Cl/I/ Mn
Sylvania

3. 100V cd/m2

6. Fluorescence and Phosphorescence

8. Excimer Formation

11. Exciplex Formation

12. History of Organic Electroluminescence
1963 Pope V um anthracene
1965 Helfrich V 5 % efficiency
1970 Williams
1982 Vincett V nm low efficiency
1983 Partridge Polymeric materials

15. Basic Principle of Organic EL
Metal (eV) Ca Mg In Al Ag Cu Au
ITO eV
Charge recombination leads to emission of fluorescence

16. Fowler-Nordheim Equation: I = AF2exp(-kf3/2/F)
F: field strength, A: material constant, f: energy difference across the interface

17. Efficiency:
= Number of photons emitted/Number of electrons injected
I/V relationship and B/V relationship

18. Tang etal, Kodak

19. ETL
Electron Transporting
Layer
HTL
Hole Transporting

20. Hole Transporting
Layer

21. Electron Transporting Materials

22. Criteria for the Materials of Emitting Layer

23. Matching of Energy Levels
TPD

24. ITO Surface Modification Layer for Hole Injection

25. Addition of
Hole Injection Layer
TPD

28. Fluorescence Dye as Dopant:
A Yellowish Light Emitting Device
Rubene

31. Red light
emitting materials

32. Dopant amounts and
Performance of the EL device

33. Rubrene as a medium for energy transfer

36. Green emitters

38. Blue Light Emitting Device
nm, 4000 cd/m2

39. White Light OLED
White = Blue + Red
Blue
Red

40. Device 1 Undoped; Device 2 Doped with 5% of red DCM2

41. Highly-bright white organic light-emitting diodes based on a single emission layer
C. H. Chuen and Y. T. Tao

42. Trilayer Device Structure

45. Recent advances on the Interfacial Problems
X. Zhou, M. Pfeiffer, J. Blochwitz, A. Werner, A. Nollau, T. Fritz, and K. Leo APL

46. They demonstrated the use of a p-doped amorphous starburst amine, 4, 48, 49-tris(N, N-diphenylamino triphenylamine )(TDATA), doped with a very strong acceptor, tetrafluorotetracyanoquinodimethane by controlled coevaporation as an excellent hole injection material for organic light-emitting diodes (OLEDs). Multilayered OLEDs consisting of double hole transport layers of p-doped TDATA and triphenyldiamine, and an emitting layer of pure 8-tris-hydroxyquinoline aluminum exhibit a very low operating voltage (3.4 V) for obtaining 100 cd/m2 even for a comparatively large (110 nm) total hole transport layer thickness.

47. Low voltage organic light emitting diodes featuring doped phthalocyanine as hole transport material
J. Blochwitz, M. Pfeiffer, T. Fritz, and K. Leo

48. Rough estimates lead to values of about 0
Rough estimates lead to values of about 0.2% luminescence efficiency for the highest doped case. However, those devices use sophisticated multi-layer designs and low-work function contacts. We believe that the major reason for the lower efficiency of our diodes is that the simple two-layer design does not prevent negative carriers injected from the Al electrode from reaching the opposite electrode due to the missing energy barrier for electrons at the Alq3–VOPc interface. This limits the probability of exciton formation and their radiative decay.

49. Graded mixed-layer organic light-emitting devices
Anna B. Chwang,a) Raymond C. Kwong, and Julie J. Brown

51. Improved efficiency by a graded emissive region in organic light-emitting diodes
Dongge Ma, C. S. Lee, S. T. Lee, and L. S. Hung

54. Metal Complexes

55. Al Complexes

56. Organic light-emitting diodes using a gallium complex

64. 210 cd/m2 with Al
2500 cd/m2 with LiF

66. Red Light Emitting Device
Based on Eu Complexes
7-137 cd/m2

67. Thickness Effect
Better ET, 820 cd/m2

68. Hole Blocking Layer

69. Phosphorescent Devices
100000cd/m2

70. Shizuo Tokito APL

74. Controlling Exciton Diffusion in Multilayer White Phosphorescent Organic Light Emitting Devices
Brian W. D'Andrade, Mark E. Thompson, Stephen R. Forrest* Adv. Mater. 2002

78. The color balance (particularly enhancement of blue emission) can be improved by inserting a thin BCP, hole/excitonblocking layer between the FIrpic and Btp2Ir(acac) doped layers in Device 2. Thislayer retards the flow of holes from the FIrpicdoped layer towards the cathode and thereby forces more excitons to form in the FIrpic layer, and it prevents excitons from diffusing towards the cathode after forming in the FIrpic doped layer. These two effects increase FIrpic emission relative to Btp2Ir-(acac).
Device 2 is useful for flat-panel displays since the human perception of white from the display will be unaffected by the lack of emission in the yellow region of the spectrum.

81. Electroluminescence in conjugated polymers
R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N. Marks, C. Taliani, D. D. C. Bradley,
D. A. Dos Santos, J. L. Bre¬ das, M. Lo» gdlund & W. R. Salaneck Nature
Wessling Approach

82. Solubilizing Groups
Red
Red
Blue
Green

84. Figure 6 Energy levels for electroluminescent diodes
Figure 6 Energy levels for electroluminescent diodes. a±c, An ITO-PPV-Ca diode before contact between the three layers, illustrating the energies expected, a, from the metal Fermi energies, assuming no chemical interactions at the interface, b, after some `doping' of the interfacial layer of PPV by Ca, setting up bipolaron' bands within the PPV semiconductor gap (note that the Fermi energy for the `doped' PPV lies between the upper bipolaron level and the conduction band), and c, after interfacial chemistry which sets up a blocking layer at the interface (as expected in the presence of oxygen). d, Energy levels for the components of a two-layer heterojunction diode fabricated with PPVand CN-PPV.

85. Unexpectedly high efficiency