CH. 3 Solar Cell Basic III: Principle

Organic Materials for Electronics and Photonics II

2

Light Emitting Diodes• Electric energy to light energy

• Materials for LED

LightElectric energy

LED

3

Mechanism of p-n Junction

C. B.

V. B.

EF

C. B.

V. B.

EFEnergy

4

Mechanism of p-n Junction

Depletion Layer

Energy

5

Mechanism of p-n Junction

+ -

h

Energy

• Forward bias

6

PLEDLED

Inorganic Organic (OLED)

Small Molecules (SMOLED)

Polymer (PLED)

PLED (Polymer Light Emitting Diode) - LED used polymer not only as the semiconductor material in LEDs but also as the composition of LED (substrate, active layer, electrode, etc.).

Advantages of PLED- low cost - low operating voltage- fast response time - full color emission- large area, flat, flexible display - easy fabrication

7

Structure of PLED

ITO Sputtering

ITO Patterning - Photolithography

ITO glass cleaning

HTL coating (PEDOT:PSS) - Spin coating

Emitting layer coating - Spin coating

Aluminum evaporation

8

Aluminum

polymerITO

Glass

Mechanism of PLED

hAnode

cathode

Polymer

+ -

Evolution of Display

CRT

LCD

PDP

Organic ELFlexible display

10

Requirement for Flexible Display

Substrate⇒ Flexible !!(Glass → Plastic)

Emitting layer ⇒ Flexible Semiconducting polymer

Electrode ⇒ Flexible electrode

Flexible packaging material

11

ITO as Flexible Electrode

1 2 3 4 5 6100

101

102

103

104

20 times

10 times

5 times

Cu

rren

t (A

)

Voltage (V)

bending Before

ITO as Flexible electrode

Require a ‘genuine’ flexible & transparent electrode!!

12

Requirements for Flexible Electrode

1. Flexibility

2. Conductivity

3. Transparency

Plastic Electrode using Conducting Polymer

13

Molecular Scale DisorderReduction of

K. Lee & S.H. LeeNature 441 (2006) 65.

σdc ≥ 1,000 S/cm

“Recent Invention of New Metallic Polyaniline”

14

Metallic PANI Electrode

Molecular Scale DisorderReduction of

K. Lee et al. Nature 441 (2006) 65.

σdc ≥ 1,000 S/cm

1 2 3 4 5 610-4

10-3

10-2

10-1

100

101

102

103

104

105

w/o bending 5 times 10 times 20 times 30 times 40 times 50 times

Cur

rent

(A)

Voltage (V)

Flexible substrate using ITO

1 2 3 4 5 610-4

10-3

10-2

10-1

100

101

102

103

104

105

w/o bending 5 times 10 times 20 times 30 times 40 times 50 times

Flexible substrate using PANI

Cur

rent

(A)

Voltage (V)

15

PANI Electrode : Flexible LED

0 2 4 6 8 10 12 14 16

50

100

150

200

250

300

350

0

200

400

600

800

1000

4 6 8 10 12 14 160.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

Lum

inou

s E

ffic

ienc

y (c

d/A

)

Voltage (V)

Bri

ghtn

ess

(cd/

m2 )

Cur

rent

Den

sity

(mA

/cm

2 )

Voltage (V)

New PANI/PEDOT:PSS/MEH-PPV/Alq3/LiF/Al

16

Flexible Electrode using Metallic PANI

PES

Active layer

PEDOT:PSS

TiOx

Al

PANI

PES

Active layer

PEDOT:PSS

TiOx

Al

PANI

PES

Active layer

PEDOT:PSS

TiOx

Al

PANI

0.0 0.2 0.4 0.6-8

-6

-4

-2

0

Jsc

~ 6.72 mA/cm2

Voc

~ 0.61 V

F.F. ~ 0.44

e ~ 1.82 %

Cu

rre

nt

De

ns

ity

(m

A/c

m2 )

Bias (V)

Flexible Solar Cell

Flexible LED

0 2 4 6 8 10 12 14 160

20

40

60

80

100

120

140

0 40 80 120

0.0

0.5

1.0

1.5

2.0

mA/cm2

Efficiency (cd/A)

Voltage (V)

Cu

rren

t D

ensi

ty (

mA

/cm

2 )

0

500

1000

1500

2000

2500 Brig

htn

ess(cd

/m2)

New PANI Electrode