oleds - introductory concepts and current research - c coward

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://en.wikipedia.org/wiki/Oled

OLED Applications


www.siemens.com/innovation

http://www.hashslush.com

An OLED TV display (left), and a solid-state OLED lighting setup (below).

Advantages of OLEDs


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://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)


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).


VS.

ALQ3 PPV

Quantum Considerations


F. Dias – Optical Spectroscopy – PG Lecture Course, Lecture 1.

Device Efficiency


(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://www.maximintegrated.com/

http://dot-color.com/2012/08/14/color-space-confusion/

Spin-Orbit Coupling


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://chemwiki.ucdavis.edu/

E-type Fluorescence (TADF)

E-type fluorescence is so called due to it first being observed in eosin.


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%.


Thank you for listening.

Any questions?


http://ww3.oled-display.net/

http://www.ecubedventures.com/oled-lighting

oleds - introductory concepts and current research - c coward

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