oled ageing modelling and compensation · imola | final workshop – barcelona – 06.05.2014. | j....

IMOLA | Final Workshop – Barcelona – 06.05.2014. | J. Kundrata, D. Bandic and A. Baric

Slide 1/17

OLED ageing modelling

and compensation

J. Kundrata, D. Bandic and A. Baric

University of Zagreb

IMOLA Final Workshop


Slide 2/17

Outline

Ageing of the OLED luminance:

Exponential model

Double-exponential model

Stretched-exponential model

Coffin-Manson ageing model

OLED ageing compensation:

Time-based compensation

Alternative compensation algorithms

Conclusion


Slide 3/17

OLED ageing (I)

Emissive (A A*) to non-emissive (B) OLED molecules

at decay rate rd

Effects (while OLED current I is constant):

Luminous efficacy k reduces

OLED voltage V increases


Slide 4/17

OLED ageing (II)

Relative luminance L/L0 decreases over time t

as the OLED current I is kept constant


Slide 5/17

Exponential decay

Half-life T1/2 ≈ 8 000 h

Relatively bad fit to measured data

2/1

2ln

0

T

t

eLL


Slide 6/17

Double exponential decay

2,2/11,2/1

2ln

2

2ln

10

T

t

T

t

eAeALL

Half-life T1/2,1 ≈ 4 000 h

Half-life T1/2,2 ≈ 150 000 h

Amplitude A1 ≈ 0.14

Amplitude A2 ≈ 0.86

Effective half-life T1/2,eff ≈ 10 400 h


Slide 7/17

Stretched exponential decay

2ln

02/1

T

t

eLL

Half-life T1/2 ≈ 12 000 h

Stretch factor β ≈ 0.8

Effective half-life T1/2,eff ≈ 10 350 h


Slide 8/17

OLED ageing compensation

OLED luminary Luminance L = constant during life-cycle

Decrease in luminous efficacy k is compensated

by increasing OLED current I

No luminance feedback on the IMOLA module:

How to keep track of the luminance degradation?

IkL


Slide 9/17

Time-based compensation - Algorithm

Every ΔT hours increase current by ΔI %

Parameter ΔI is updated during algorithm due to

the stretched exponential model

1/2

ln2

1

t T t

TI t e


Slide 10/17

?)(2/12/1 ITT

Time-based compensation - Luminance

Example Period ΔT = 1000 h

Is T1/2 equal to T1/2

when current varies?

1/2

ln2

1

t T t

TI t e


Slide 11/17

Coffin-Manson fatigue model

Ageing factor n

1/2 1 .nL T c const

1/2 2 .nI T c const


Slide 12/17

Time-based compensation - Revisited

Ageing compensation fails


Slide 13/17

Time-based compensation v2

Ageing compensation fails when the current

increases with time

ΔI needs to be updated w.r.t. the ageing model

Ageing factor n > 1 exponential rise of

OLED current

ln2

( ) 1n

t T tc II t e


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Time-based compensation v2

Example n ≈ 1.5

How to determine End-of-Life?


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Alternative compensation algorithms

Voltage-based compensation:

Increase in OLED voltage is used

to keep track of the degradation

Power-based compensation:

OLED is driven with a waveform (ΔI)

ΔU = f(ΔI) and PHEAT = g(ΔU)

PLIGHT = PIN - PHEAT

NXP patents:

● US 2011/0080113 A1

LUMINANCE

FALLS

VOLTAGE

RISES

I = constant


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Conclusion

OLED luminance decays with time:

Stretched-exponential models the decay

Coffin-Manson models the decay rate

Time-based compensation needs:

Luminance decay parameters – β, T1/2

Coffin-Manson fatigue parameters – c, n

Alternative compensation algorithms:

Voltage-based

Power-based


Slide 17/17

Thanks!

oled ageing modelling and compensation · imola | final workshop – barcelona – 06.05.2014. | j....

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