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OLEDs – Introductory Concepts and Current Research
C. Coward
OEM GroupSupervisors – Prof. A.P. Monkman & Dr. F.B. Dias
Talk Outline
1. OLEDs – What they are, where and why they’re used, where they came from and how they work.
2. Device Efficiency – What controls efficiency, and previously tested ways to increase it.
3. Current Research – New methods being explored to improve OLED performance.
http://community.dur.ac.uk/oem.group
What is an OLED?
An OLED is a device that emits light in response to an electric current.
http://community.dur.ac.uk/oem.group
http://en.wikipedia.org/wiki/Oled
OLED Applications
http://community.dur.ac.uk/oem.group
www.siemens.com/innovation
http://www.hashslush.com
An OLED TV display (left), and a solid-state OLED lighting setup (below).
Advantages of OLEDs
http://community.dur.ac.uk/oem.group
www.oled-info.com/oled-tv
http://www.smallhd.com/products/dp7-pro/display.html
History
C.W. Tang (left) and Steven Van Slyke (right) created the first ever OLED in 1987.
http://community.dur.ac.uk/oem.group
http://www.oled-info.com/steven-van-slykehttp://en.scut.edu.cn/
Working Principles
Anode (e.g. Indium Tin Oxide)
~ 3-5V DC
Light
Emissive Layer
Cathode (e.g. Calcium or Sodium)
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Glass
E.F. Schubert – Light-Emitting Diodes (Cambridge Univ. Press).
Material Technologies
The two competing material architectures used in OLEDs are small molecules (left), and polymers (right).
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VS.
ALQ3 PPV
Quantum Considerations
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F. Dias – Optical Spectroscopy – PG Lecture Course, Lecture 1.
Device Efficiency
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(i) Injection of electron and hole
(ii) Capture to form exciton
(iii) Radiative decay
(iv) Light emissioneff = rst q ext
Optical outcoupling.Ratio of excitons to charge injected.
Fraction of excitons that can radiatively decay (i.e. Singlets).
Efficiency of radiative decay of singlet excitons (PL efficiency).
Quantum efficiency = eff = photons out
charges flowing in circuit
The Photopic Response
http://community.dur.ac.uk/oem.group
http://www.maximintegrated.com/
http://dot-color.com/2012/08/14/color-space-confusion/
Spin-Orbit Coupling
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http://www.nature.com/srep/2013/130913/srep02653/full/srep02653.html
P-type Fluorescence (TTA)
P-type fluorescence is so called due to it first being observed in pyrene.
http://community.dur.ac.uk/oem.group
http://chemwiki.ucdavis.edu/
E-type Fluorescence (TADF)
E-type fluorescence is so called due to it first being observed in eosin.
http://community.dur.ac.uk/oem.group
http://www.nature.com/nature/journal/v492/n7428/fig_tab/nature11687_ft.html
Talk Summary
1. OLEDs are organic, light-emitting diodes that produce electroluminescence in response to current. They can be printed onto ultra-thin, flexible substrates.
2. OLEDs are currently used in many display containing devices such as TV’s and mobile phones, as well as being used in solid-state lighting systems.
3. New research hopes to increase the efficiency of OLEDs closer to its maximum theoretical limit of 100%.
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Thank you for listening.
Any questions?
http://community.dur.ac.uk/oem.group
http://ww3.oled-display.net/
http://www.ecubedventures.com/oled-lighting