PLEDPLEDPolymere Light Emitting Diodey g g

Lecture: Incoherent Light SourcesLecture: Incoherent Light Sources SS 2013

Adrian Podlinski

Differentiation of OLEDsDifferentiation of OLEDs

• SMOLED (small molecule organic light‐emitting diodes)g )

PLED (P l li h i i di d )• PLED (Polymer light‐emitting diodes)

• PHOLED (Phosphorescent organic light‐itti di d )emitting diode)

Working PrincipleWorking Principle

StructureStructureSMOLED

StructureStructurePLEDPLED

LEP: Light‐emitting PolymerLEP: Light emitting PolymeriL: InterlayerHiL: Hole Injection Layer

Semiconducting PolymersSemiconducting Polymers

• Conjugated‐π‐Electron‐System• Contiguous sp2 hybridized carbon centersContiguous sp hybridized carbon centers• P‐orbitals form a one‐dimensional electronic b dband

• Higher conductivity higher degree of g y g gcrystallinity and better alignment of the chains

Conducting PolymerConducting Polymer

• Conductivity can be increased byoxidation/reduction

Light Emitting PolymersLight‐Emitting Polymers

• PPV was suggested for lighting application in 1990

• Synthesis:

Light Emitting PolymersLight‐Emitting Polymers

• By substituting a polymer different properties can be changed, like:g– StabilitySolubility– Solubility

– Conductivity– Emission spectrum

Light Emitting PolymersLight‐Emitting Polymers

FabricationFabrication

k i i• Ink‐Jet‐Printing

+ High resolution + Large area‐Uneven Emission because of different layer thicknesses 

FabricationFabrication

i i• Spin‐Coating

+ Uniform films+ Simple R&D process‐ High wastageHigh wastage‐ Not ideal for big production quantities

Phosphorescent OLEDsPhosphorescent OLEDs

• 2 types of excitons are possible – statistical ratio singlet:triplet =1:3g p

Phosphorescent OLEDsPhosphorescent OLEDs

• In order for triplet excitons to emit, spin‐orbit coupling is requiredp g q

• This effect is strong in heavy atomsT i i l did• Transition metals are common candidates to enable phosphorescence from organicmolecules

• Doping a host polymer with• Doping a host polymer with an organometallic complex

AdvantagesAdvantages

• Light weight & flexible plastic substrates• Wider viewing angles & improved brightnessWider viewing angles & improved brightness• Better power efficiency and thickness• Response time

DisadvantagesDisadvantages

• Lifespan• Color balance issuesColor balance issues• Outdoor performance• High Cost• Power consumption increases for whitePower consumption increases for whiteimages

OLED / LEDOLED / LED

ApplicationsApplications

Flexible OLEDsFlexible OLEDs

• Two major challenges are the backplane and the encapsulation.p

SourcesSources

htt // l d i f /• http://www.oled‐info.com/• http://www.cdtltd.co.uk/

// /• http://www.sigmaaldrich.com/technical‐documents/articles/material‐matters/light‐emitting polymers htmlemitting‐polymers.html

• http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2000/advanced‐ry/laureates/2000/advanced‐chemistryprize2000.pdf

• http://www nature com/nature/journal/v347/n6http://www.nature.com/nature/journal/v347/n6293/pdf/347539a0.pdf

PLEDPLEDPolymere Light Emitting Diodey g g

Incoherent Light Sources SS 2013Incoherent Light Sources SS 2013Adrian Podlinski