1. Daniel Bowser Fernando Robelo
Light Emitting Diodes
Daniel Bowser
Fernando Robelo

2. Contents Basics of LEDs Current LED technology Band Gap Semiconductor
Organic
Frontier LED technology
Quantum Dot
Conclusions

3. Basics of LEDs

4. Light Emitting Diodes (LEDs)
Semiconductor based radiation source
photons emitted when electrons recombine with holes
Visible, Infrared, and Ultraviolet Emission

5. Applications of LEDs Indicators and Signs Lighting Fiber optics
street lights, aviation, display background, color changing, small durable devices, infrared emission, vehicle lighting
Fiber optics
Sustainable lighting
energy, economical

6. 3 Types of LEDs Current LED technology: Ultraviolet and blue
Band Gap Semiconductor
Ultraviolet and blue
White
Organic (OLEDs)
Frontier Research:
Quantum Dot (QdotLEDs)

7. Current LED Technology Band Gap Semiconductor
Organic Frontier Research
Quantum Dot

8. Band Gap Semiconductor Based LEDs
First LED to be developed (1927)
Most widely used
Most economical to produce
p/n junction semiconductor
typically made of III/V compounds

9. Band Gap Semiconductor Based LEDs
p-n junction
no voltage applied

10. Band Gap Semiconductor Based LEDs
p-n junction
forward voltage bias

11. Band Gap Semiconductor Based LEDs
Unfortunately its not that simple...
-modern LEDs do not use just one p-n junction composed of two materials
-hundreds of p-n junctions between highly complex crystal structures
-band gaps must be carefully engineered to produce light of the desired color

12. Current LED Technology:
Band Gap Semiconductor
Organic
Frontier Research
Quantum Dot

13. Organic LEDs
LED that uses an organic semiconductor as the luminescent layer
Thin, flexible, with some transparent components
Broad applications in displays and mobile devices
Magnified OLED phone display

14. Organic LEDs

15. Organic LEDs Composition of small molecule OLED semiconductors
Emissive Layer
Organometallic chelates
Fluorescent and
Phosphorescent Dyes
Conductive Layer
Dendrimers for charge transport

16. Current LED Technology
Band Gap Semiconductor
Organic
Frontier Research
Quantum Dot

17. Uses of Colloidal Quantum Dots
Photovoltaics
Photodetectors
Light Emitting Diodes

18. Physical Structure of Qdot LED

19. Electronic Structure of Qdot LED

20. Purpose of Research
To determine the ability to dramatically enhance quantum efficiency of exciton recombination by tuning distance between PbS quantum dots in active layer LED

21. LED performance and interdot distance

22. Current density-voltage characteristic

23. Emission Spectra and infrared image of LEDs

24. Qdot LED Advantages and Disadvantages
Low cost and may be directly integrated
Difficult to control exciton dissociation and recombination (unstable)
Greater color range, as well as color accuracy
100 times brighter than LCD displays
Greater flexibility and improve lifetime

25. Conclusions

26. Current LEDs compared to current lighting alternatives
Advantages:
more energy efficient
longer lifetime
wider range of applications
Disadvantages:
high initial price
quality of light produced

27. Future Research
Competition between exciton dissociation an radiative recombination dominates the variation of EQE with different linker molecules
Performance improvement are possible based on the understanding of the limitations of charge transport and injection rates can optimize LED efficiency and radiance

28. References Primary paper being discussed: Other sources:
Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control.
Other sources:

29. Questions?