Daniel Bowser Fernando Robelo Light Emitting Diodes Daniel Bowser Fernando Robelo

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

Basics of LEDs

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

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

3 Types of LEDs Current LED technology: Ultraviolet and blue Band Gap Semiconductor Ultraviolet and blue White Organic (OLEDs) Frontier Research: Quantum Dot (QdotLEDs) http://www.photonics.com/Article.aspx?AID=24915,http://www.arlty.com/faq/, http://en.wikipedia.org/wiki/Led

Current LED Technology Band Gap Semiconductor Organic Frontier Research Quantum Dot

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 http://en.wikipedia.org/wiki/Category:III-V_compounds

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

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

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

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

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

Organic LEDs http://www.circuitstoday.com/workng-of-organic-led-oled

Organic LEDs Composition of small molecule OLED semiconductors Emissive Layer Organometallic chelates Fluorescent and Phosphorescent Dyes Conductive Layer Dendrimers for charge transport http://en.wikipedia.org/wiki/Organic_light-emitting_diode

Current LED Technology Band Gap Semiconductor Organic Frontier Research Quantum Dot

Uses of Colloidal Quantum Dots Photovoltaics Photodetectors Light Emitting Diodes

Physical Structure of Qdot LED

Electronic Structure of Qdot LED

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

LED performance and interdot distance

Current density-voltage characteristic

Emission Spectra and infrared image of LEDs

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

Conclusions

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

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

References Primary paper being discussed: Other sources: Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control. http://www.nature.com/nnano/journal/v7/n6/abs/nnano.2012.63.html Other sources: http://onlinelibrary.wiley.com/doi/10.1889/1.2785443/abstract http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6248162 http://onlinelibrary.wiley.com/doi/10.1889/1.3500495/abstract http://onlinelibrary.wiley.com/doi/10.1889/1.1927730/abstract http://photonics.intec.ugent.be/education/ivpv/res_handbook/v1ch12.pdf

Questions?