Organic Light Emitting Diode OLED - Télécom ParisTech€¦ · • 1987 Organic light-emitting diode OLED ... 5.7-inch HD Super AMOLED display 1920 x 1080 resolution ... rollable

Yvan BONNASSIEUX 06/02/2014

OLED: Organic Light Emitting Diode

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Organic Light Emitting Diode OLED

[email protected]



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SUMMARY

ØIntroduction !

ØOrganic material !

ØOLED: Organic Light Emitting Diode !

ØOLEDs today !

ØOLED futur ?



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Introduction



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Introduction (I)Organic materials

•  Organic:)Rela-ng)or)belonging)to)the)class)of)chemical)compounds)having)a)carbon)basis)

•  Include)polymers)and)small)molecules)

•  Polymer:*Large*molecule*composed*of*a*repea4ng*structural*unit*(monomer)*

•  Small*molecules*M<800

•  Until recently, polymers were known as electrical insulators •  In 1977, discovery of electrical conductivity in doped polyacetylene

•  Nobel prize in chemistry in 2000 to Alan Heeger, Alan McDiarmid and Hideki Shirakawa •  Organic electronic devices came out ten years later

•  1986. Organic photovoltaic cell OPV (Ching W Tang, Kodak) •  1986. Organic field-effect transistor OFET (H Koezuka, Mitsubishi) •  1987 Organic light-emitting diode OLED (Ching W Tang, Kodak)

Conducting polymers



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Introduction (II)Why organic?

•  Organic(materials(

•  Large'diversity'

•  Low'cost,'large'area,'flexible'substrates'

•  Manufacturable'via'prin;ng'techniques'

•  �Green��technology'

•  Drawbacks(

•  Low'performance'

•  Poor'stability'

•  Small'market'(except'OLEDs)'

Organic electronic devices

Organic field-effect transistors (OFET)

Organic light-emitting diode (OLED)

Organic light-emitting diode (OLED)



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Organic material



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Conjugated molecules (I)Benzene Conjugated = alternation of simple and double bond

benzene: C6H6

6 delocalize electrons on all the molecule

Frontier orbitals •  HOMO:%Highest%Occupied%Molecular%Orbital%

•  LUMO:%Lowest%Unoccupied%Molecular%Orbital



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C CH H

HH

*

*

σ bond ⇒ ensure the maintenance of the molecule

π bond ⇒ electrical properties

Double bond: hybridization sp2 (superposition orbitals s et pz)

Ethylene

Conjugated molecules (II)



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•  HOMO:%Highest%Occupied%Molecular%Orbital%

•  LUMO:%Lowest%Unoccupied%Molecular%Orbital

n Ethylène Octatétraène Butadiène Polyacéthylène

Energy

π* (LUMO)

π (HOMO)

π* (LUMO)

π (HOMO)

π* (LUMO)

π (HOMO)

Number of motif

π* (LUMO)

π (HOMO)

Gap

Frontier orbitals: energy bands (I)



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Frontier orbitals: energy bands (II)



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Main properties (I)

Organic(solids! Inorganic(solids!

Binding(energy! weak((Van(der(Walls)! strong((covalent)!

Mechanical(strength! weak! strong!

Charge(carriers! localised! delocalised!

Polarisa=on! strong! weak!

Charge(transport! hopping! band!

Charge(mobility! ~(1(cm2/Vs! ~(1000(cm2/Vs!

Exciton! FrenkelItype! WannierItype!



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Low mobility: 10-4 to 1 cm2.V-1.s-1

Doping is a complexe process No free charge (~1010) in intrinsic material Always in full depleted mode Current: electrode injection or photo-generation P and N type only defined by electrode WF (Work function) Gaussian DOS (Density of states) Transport mechanism GVRH (Gaussian Variable Range Hopping)

Main properties (II)



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OLEDs



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W. Helfrich et al. Phys. Rev. Lett. 14, 229 (1965)

Electroluminescence was observed from single crystals of anthracene.

5 mm thick crystalEl quantum efficiency ~ 1-5% High driving voltage

Good understanding of the basic physical processes involded in electroluminescence like double injection, charge carrier migration, electron-hole capture (exciton formation),and light emission (fluorescence)

History



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OLEDS principle (I)



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Multilayers interest

OLEDS principle (II)



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Metallic electrodes

OLEDS principle (III)



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OLEDs conduct in forward bias and do not conduct under reverse bias. The impedance drops exponentially with V for V>Vth.

Brightness is proportional to the current flowDiode behavior

Electrical and optical characteristic

OLEDS principle (IV)



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Pope (1963) Helfrich (1965)

Thick crystals

Efficiency & stability

Heterostructures

1985 20021965

HBL Hole Blocking layer: Exciton confinementPLED

Doped transport layers K. Leo, U. Dresden

Cathode

Anode

EML

Monolayer

~~~~

2-layers

EK US patent #4539507

Cathode

Anode

EML

HTL

Cathode

AnodeHTL

EML

Doped-EML

EK US patent #4769292

Cathode

Anode

EML/dopedHTL

ETL

HIL

HBL

Multilayers

Cathode

Anode

EML/dopedHTL

ETL

P-doped

N-doped

PIN

OLEDS principle (V)



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Color



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Encapsulation (I)



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No really standardized measurement method (DC vs pulsed constant current, brightness level …)

Device lifetime usually defined as : Mean time to half-brightness

Degradation of OLED devices is one of the main issues. Degradation phenomena occur both under operating condition as well as under storage.

Encapsulation (II)



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Source : Vitex

Substrate

OLED

Barrier coating

Encapsulation (III)



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Oled deposition: evaporation



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Oled deposition: printing



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OLEDs today



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OLED display (I)

!  Very thin !  Light weight !  Fast response time !  High brightness !  Large viewing angle !  Low power consumption

OLEDs display strengths

Active matrix pixel



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OLED display (II)



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OLED display (III)

Samsung Galaxy Note 3. 5.7-inch HD Super AMOLED display 1920 x 1080 resolution

LG G Flex 6 inch HD AMOLED display 1280 x 720 resolution thickness 0.44 mm, 7.2g



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OLED display (IV)

55-inch class WRGB OLED TV Only 4 millimeters (0.16 inches) thin and weighing less than 10 kilograms (22 pounds) near 8.000 €



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OLED ligthing (I)



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OLED display (II)



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OLEDs future?



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Conformable display



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Flexible display



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Pliable display

rollable displays



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Stretchable electronics



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Wearable display



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Micro & transparents displaysMicro écrans (lunettes)

Lens electronics



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Micro & transparents displays



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Conclusion

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Organic Light Emitting Diode OLED - Télécom ParisTech€¦ · • 1987 Organic light-emitting diode OLED ... 5.7-inch HD Super AMOLED display 1920 x 1080 resolution ... rollable