Transcript Polymer Light Emitting Diodes

Organic Materials for Electronics and Photonics II
CH. 3 Solar Cell Basic III: Principle
Light Emitting Diodes
• Electric energy to light energy
Electric energy
LED
Light
• Materials for LED
2
Mechanism of p-n Junction
C. B.
C. B.
EF
Energy
EF
V. B.
V. B.
3
Mechanism of p-n Junction
Depletion Layer
Energy
4
Mechanism of p-n Junction
• Forward bias
+ -
Energy
h
5
PLED
LED
Small Molecules (SMOLED)
Inorganic
Organic (OLED)
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
- fast response time
- large area, flat, flexible display
- low operating voltage
- full color emission
- easy fabrication
6
Structure of PLED
ITO Sputtering
ITO Patterning - Photolithography
ITO glass cleaning
HTL coating (PEDOT:PSS)
- Spin coating
Emitting layer coating
- Spin coating
Aluminum evaporation
7
Mechanism of PLED
Aluminum
polymer
ITO
Glass
+
-
Polymer
cathode
Anode
h
8
Evolution of Display
CRT
Flexible display
LCD
PDP
Organic EL
Requirement for Flexible Display
Flexible packaging
material
Electrode
⇒ Flexible electrode
Emitting layer ⇒ Flexible
Semiconducting polymer
Substrate⇒ Flexible !!
(Glass → Plastic)
10
ITO as Flexible Electrode
ITO as Flexible electrode
4
10
Before
bending
3
Current (A)
10
5 times
2
10
10 times
20 times
1
10
0
10
1
2
3
4
5
6
Voltage (V)
Require a ‘genuine’ flexible &
transparent electrode!!
11
Requirements for Flexible Electrode
1. Flexibility
2. Conductivity
3. Transparency
Plastic Electrode using
Conducting Polymer
12
“Recent Invention of New Metallic Polyaniline”
K. Lee & S.H. Lee
Nature 441 (2006) 65.
Reduction of
Molecular Scale Disorder
σdc ≥ 1,000 S/cm
13
Metallic PANI Electrode
K. Lee et al. Nature 441 (2006) 65.
Reduction of
Molecular Scale Disorder
σdc ≥ 1,000 S/cm
5
Flexible substrate using ITO
5
10
4
4
10
10
3
Current (A)
2
10
1
10
0
10
w/o bending
5 times
10 times
20 times
30 times
40 times
50 times
-1
10
-2
10
-3
10
-4
Current (A)
3
10
10
Flexible substrate using PANI
10
10
2
10
1
10
w/o bending
5 times
10 times
20 times
30 times
40 times
50 times
0
10
-1
10
-2
10
-3
10
-4
1
2
3
4
Voltage (V)
5
6
10
1
2
3
4
Voltage (V)
5
6
14
PANI Electrode : Flexible LED
250
200
150
0.30
0.28
0.26
0.24
0.22
0.20
0.18
0.16
0.14
4
1000
2
300
800
600
14
12
10
8
Voltage (V)
6
16
400
100
200
50
0
2
Brightness (cd/m )
New PANI/PEDOT:PSS/MEH-PPV/Alq3/LiF/Al
Luminous Efficiency (cd/A)
Current Density (mA/cm 2)
350
4
6
8
10
12
14
0
16
Voltage (V)
15
Flexible Electrode using Metallic PANI
Efficiency (cd/A)
140
2500
2.0
120
2000
1.5
100
1.0
80
1500
0.5
60
mA/cm2
0.0
0
40
40
80
1000
120
0
0
2
4
6
8
10
12
14
0
16
Voltage (V)
New PANI Electrode
2
Current Density (mA/cm )
Flexible Solar Cell
Al
TiOx
Active layer
PEDOT:PSS
PANI
PES
0
Jsc ~ 6.72 mA/cm
-2
2
Voc ~ 0.61 V
F.F. ~ 0.44
e ~ 1.82 %
-4
-6
-8
0.0
0.2
0.4
0.6
Bias (V)
16
2
500
20
Brightness(cd/m )
Current Density (mA/cm2)
Flexible LED