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Georges ZISSIS

LAPLACE, Univ. de Toulouse 3

georges.zissis@laplace.univ-tlse.fr

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Electroluminescence from semiconductors 1907 1st coloured LED 1962 1st white LED 1995 Application in Lighting 2000

Electroluminescence from organics 1963 1st multi-layer OLED 1987 Lighting applications 2010

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H.J. Round, Electrical World 49, 309 (1907)

A currious phenomenon observed…

Cpt Henry Joseph Round (Marconi Co)

Carborundum (SiC)

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5 mm LED High Brightness LED

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High luminance Excellent saturated colors High luminous efficacy High conversion efficacy Small dimensions & light weight Robust Long life span Low voltage power supply Easy to supply and dim

Point Sources

Robust

Multi-chip modules

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Energy saving High Luminous Efficacy High Energy Conversion Capacity

Long Lifespan

Direct retrofitting of other lamps & Usable in any luminaire

Stable Light No flickering nor blinking Constant along lifespan

Avoid any risks and pollution Heat UV & blue light EMC Hazardous substances Electrical Shock Hazard

Compact et light weight

Cheep & rapid return on investment

Instantaneous switch-on & Dimming capacity

Recyclable

Good Light Quality Color Rendering Index Color Temperature Spatial beam Uniformity Spatial color Uniformity

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(a)

(b)

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DEFWHM = 1,8kBT

nmax = Eg

h +

kBT

2h =

c

lmax

An LED is nearly monochromatic Spectral width is very small The colour changes with junction

temperature

Wave vector k

Ene

rgy

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1. Colour mixing (RGB or more)

Limited gamut Unacceptable colour temperature Low Colour Rendering Index (CRI) Important optical losses Non-intuitive control

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2. Mixing Blue + Yellow

Low conversion efficacy Yellow “Hallo” effect Bad CRI (at least with B-Y mixing) Unpleasant colour temperature

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3. UV-LED + Phosphors

Colour is depending on phosphor Nice CRI Moderate efficacy

UV solarisation of plastic parts Low UV power

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Record LED

(faible puissance)

Record LED

(forte puissance)

Laboratory Records: 249 lm/W (cold white low power LEDs) 180 lm/W (cold white high power LEDs)

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Wav

ela

ngth

Wavelenght (nm)

WP

E (

%)

Effic

acy (

lm/W

)

Flu

x (

lm)

Current

Junction Temperature

Temperature (°C)

Re

lative

lig

ht

(%)

Chip

are

a

Area (mm2)

Effic

acy (

%)

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LED magazine, 51 week news letter, November 2007

Age (h)

Rel

ativ

e F

lux (

%)

Closed Semi-closed Open

26 W LED spot

Postulate

Lifespan of LED is 50 000h

That’s is depending on the used

extrapolation scheme

JELMA journal No.495

Age (h)

Rela

tive F

lux (

%)

JE

LM

A jo

urn

al N

o.4

95

(Ap

ril 20

08

)

Linear

Log

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Spe

ctru

m

Current (mA)

Rela

tive inte

nsity (

a.u

.)

20 °C

40 °C

Int

ens

ity

Lifespan

Junction temperature(°C)

Lif

esp

an (

h)

Electric parameters

Voltage (V)

Cur

rent

(m

A)

LED A LED C

LED B

Tc is modified

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For evacuating conducted heat a sink in need

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Professional Consumer

©ADEME-CitaDEL project, 2010

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100 W Inc. lamp (14 lm/W): 1400 lm

12 W LED (83

lm/W): 996 lm

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Did-you have yet install LED systems?

NO

YES

NO

YES

NO

YES

More than 4 on 5 installers had yet used LEDs

Only 10% had experienced problems !!!

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Lifetime increases

Lifetime decreases

Light is warmer

Light is colder

More lumens

Less lumens

Lifetime increases Lifetime decreases Light is warmer Light is colder More lumens Less lumens

What will happen when LED temperature increases?

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The Electrical Safety Office (ESO) is conscious of increasing safety concerns as new technology LED tubes are used to replace fluorescent lamp tubes in both commercial and household environments. The ESO has raised awareness of the danger of working with LED tubes… ESO investigations indicate there is currently no specific electrical safety product standard for these new LED technology products.…

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Some remarks after deconstruction

Bad manual soldiering

Unreliable wiring

Low quality components

Low quality chemical capacitors

“Hot” points

Low mechanical quality

©ADEME-CitaDEL project

10 products on 20 demonstrated more than 80% Harmonic Distortion! (EMC European directive EN 61000-3-2/A2: THD<15%)

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Recognized Flickering negative effects (typical frequency from 3 Hz to 70 Hz) o Neurological problems, including

epileptic seizure o Headaches, nausea fatigue, blurred

vision, eyestrain o Apparent slowing or stopping of motion, o Reduced visual task performance o Distraction o Autistic vision problem

Invisible Flickering may have also some effects (not really known) o ambient flicker at imperceptibly high

frequencies can penetrate to the neural site for flicker adaptation, which is presumed to be in primary visual cortex

Fast movement causes flicker to become more obvious – The stroboscopic effect, Phantom arrays, Ghost images… Women more sensitive to flicker than men, younger people more than older. Two of the most important parameters influencing indirect perception of stroboscopic effects are frequency and amount of modulation

Possible positive effects of flickering o Remediation of Intermittent Central

Suppression o 10 Hz flicker could improve recognition

memory in older people o Flicker may induce Brightness

Enhancement

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Impact on Retina after prolongated exposure

Glare

Eye Glare response

[Bullough, 2009]

Some LEDs have high luminance 106 cd/m2…

(Sun: 1,6×109 cd/m2)

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Cycle analysis (LCA) is primarily a method to measure the environmental impacts of various economic activities and, throughout the life cycle of the product or process.

LCA can identify the points on which a product can be improved and designed to prevent impacts from human activities.

LCA does not include economic aspects.

Raw material

acquisition

• Refining

• Transport

Productio

n

Packing Distributio

n Sales

Installation

Use

End-of-life

• Collection

• Transport

• Treatmen

t

Wastes

(Solid, liquid,

gaseous,

heat,

radioactivity…

)

Energy

recoverin

g

Component

Recovering

Material

Recovering

Repairing

Conception, R&D,

Industrialization,

Marketing

Inputs

(Energy,

Materials,

Water,

land-use)

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An lamp absorbs electrical power in watts and produces a luminous flux expressed in lumens

A lamp has an economic lifespan expressed in thousands of hours

In a lighting system a lamp is associated with a luminaire and / or a power supply.

Each component of the system to his own lifespan and his own production lines.

To compare different technologies, the usual choice of functional unit is the amount of light generated during its economic life,

expressed in million lumen-hours (Mlm.h)

Incandescent Lampe 60 W

900 lm 1 000 h

~22 lamps (GLS)

Compact Fluorescent Lamp 15 W

900 lm 8 500 h

~3 lamps (CFL)

LED Lamp 12,5 W 800 lm

25 000 h

~1 lamp (LED)

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Semiconductor industry uses solvents, toxic substance LED productin requires more « gray » energy Transport is more impacting

ISO 14040 LCA – from cradle–to-grave

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2011: 16 LEDs/lamp, 64 lm/W, 25 kh 2015: 5 LEDs/lamp, 138 lm/W, 40 kh

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Quantité

(tn

)

Primary

production

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Energy saving High Luminous Efficacy High Energy Conversion Capacity

Long Lifespan

Direct retrofitting of other lamps & Usable in any luminaire

Stable Light No flickering nor blinking Constant along lifespan

Avoid any risks and pollution Heat UV & blue light EMC Hazardous substances Electrical Shock Hazard

Compact et light weight

Cheep & rapid investment return

Instantaneous switch-on & Dimming capacity

Recyclable

Good Light Quality Color Rendering Index Color Temperature Spatial beam Uniformity Spatial color Uniformity

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Markers

Signs

Decorative Lighting

200

3

2005

General Lighting

2020-…

70 – 100 lm/W

15 - 40

lm/W

Architectural Lighting

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First commercial LED

Electroluminescence from anthracene

Discovering electrical conduction of poly-acethylene films (π-conjugated materials)

2000 Nobel

A. Hegger

A. McDiarmid

H. Shirakawa

First multi-layer OLED (C.Tang et S. Van Slyke, Eastman Kodak)

1997

1962

1963

Crystals 1977

Thin films

1987

Heterojunctions

Applications

1990

Polymers

2002 2003 2009 2010

1907 Electroluminescence Discovering (SiC)

Electroluminescence from polymers (Cambridge)

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Luminous efficacy is rapidly increasing First announcement by Kodak (1987)

General Electric: 15 lm/W (January 2005) Philips-Novaled: 32 lm/W (June 2006) Osram: 40 lm/W (September 2006) Univ. Displ. Co: 63 lm/W (October 2006) Univ. Displ. Co: 102 lm/W (July 2008)

To be follow…

May 2004: 1,000 cd/m2 - Uniformity: 1.1

(obtained from 2,2” panel).

UDC

March 2004: 61 x 61 cm

OLED

GE

June 2006: 32 lm/W and 20,000h life

span @ 1,000 cd/m2

Philips-Novaled

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An OLED is a Light Emitting Diode based on organic semi-conductors

Inorganic semi-conductor junction AC rectifier character due to PN junction Excitons (e--holes) are delocalised in the crystal: Energy bands Electrical mobility decreases with temperature Doping is necessary for getting free carriers Hetero-structures are limited due to crystal mesh mismatch Almost monochromatic emission linked to the energy gap

Organic semi-conductor stack AC rectifier character due to work function difference between the two electrodes used for the carrier injection Excitons (e--holes) are localized to single molecule Electrical mobility increases with temperature but stays very low Doping is not necessary for getting free carriers: they are injected from electrodes Structures choices are almost unlimited Large emission covering visible spectrum (molecular bands, mixing…)

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Polymers

An OLED is based on a stack of organic semi-conductors

Tw

o T

ech

nolo

gies Small molecules Cathode

(metal)

Anode (ITO)

Substrate

Organic layer(s)

Light

PPV Polyfluorene

Organic layer thickness ~100 nm Applied voltage ~10 V Electric field ~1010 V/cm

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pz π

π* Conduction “band”

π

π*

Valence “band”

GA

P +

LUMO

HOMO

The central wavelength, λ0, is proportional to the molecular

chain length

We get a unique molecular band centred around λ0

Blue O-LED produced at LAPLACE

LUMO (Lowest Unoccupied Molecular Orbital) HOMO (Highest Occupied Molecular Orbital)

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Transparent

Cathode

Organic

Layer

Transparent

Anode

Transparent

Substrate

Classic configurations

Transparent Configuration

Bottom emitting Top emitting

The Journal of the International Association of Physics Students

Univ

ers

al D

isp

lay C

orp

ora

tion

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G. Gu et al., J. Appl. Phys. 86,4076

(1999)

Sandwich Flat dot/stripe

A.R. Duggal et al.,

Appl. Phys. Lett. 80,3470

(2002)

Down conversion & Colour mixing

RGB mix YB mix

Stripe J. Jacobs et al.,

IEEE IAS (2007)

Host/Donor system

Large spectrum issued from "molecular

engineering”

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All colours are possible (no green gap) High colour quality (saturation) High CRI (molecular bands) High luminous efficacy Lambertian intensity distribution Long lifespan Low temperature drift Excellent mechanical behaviour (Flexible, bendable…) Extremely light and thin Easy to produce at low cost (R2R) Low carbon footprint Dimmable

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Aircrafts

Trains

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OLE

D C

hri

stm

as t

ree

(G

ener

al E

lect

ric)

O

LE

D w

edding d

ress

(Alison L

ewis e

-Tex

tile)

OLE

D p

illo

w

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15

NEC Lighting

582 x 582 x 18

Koizumi Lighting

Technology

1050 x 250 x 10

Matsushita Electric

Works

213 x 139 x 26

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15cm

15cm

Lighting Fair 2007

Luminance 5000 cd/m2

Yonezawa City (Japon) OLED Café !

Courtesy J. Kido, 2009

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Courtesy J. Kido, 2009

Ligh

ting Fair 2

007

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Those gathered at the recent Optic & Photonics Conference in San Diego: Life span of more than 12,000 hours and a system efficacy of 71 lm/W.

In addition, these OLED lights are completely cool to the touch

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LG Chem Targets US DoE Targets

Source: Solid-State Lighting Research and Development

Multi-Year Program Plan, DoE Report, 2013 and 2011.

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Understanding aging Enhance light extraction Increase power Discover new molecules Enhance lifespan Enhance encapsulation Increase uniformity Lower production costs Optimise power supplies

1350cd/m2

1610cd/m2

2010cd/m2

1730cd/m2

1800cd/m2

Point de

rupture

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Yole Développement says that it will be difficult for OLED panels to make any major inroads into the lighting industry, but the technology should benefit

from process improvements in 2014. By 2020, it believes that the market could be worth $1.7 billion - though that would be tiny in comparison to the OLED

display market.