有機光電半導體材料及其
未來之應用
郭 宗 枋 助理教授
Institute of Electro-Optical Science and Engineering,
National Cheng Kung University, Tainan, Taiwan 701
成功大學 光電科學與工程研究所
01/16/2007
Outlines
• Semiconductors
• Organic semiconductors (energy and
delocalization of charge carriers)
• OLEDs and PLEDs 基礎原理和應用
• Organnic photovoltaic and solar cells
• Conclusions
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Fundamental science of inorganic
semiconductors
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Typical Semiconducting Materials
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Energy Band Diagram of a conductor,
semiconductor, and insulator
(a) a conductor
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(b) a semiconductor
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(c) an insulator
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Beginning of orgnaic semiconductor (π bonding)
Side-by-Side Bonding
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Conjugated (共軛): alternatively doublesingle bonds
CH CH CH CH CH CH
單鍵
雙鍵
H
C
H
C
C
H
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H
C
C
H
H
C
C
H
H
C
C
H
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H
C
C
H
H
C
C
H
C
C
H
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Bang Gap of Polyacetylene
Band Gap
………..
……
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NCKU Institite of Electro-Optical
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Conjugated polymer
Alternating single-double bonds
Sigma bond
Delocalized  electron cloud
http://www.cdtltd.co.uk
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NCKU Institite of Electro-Optical
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Creating new materials from old materials
PPP
PA
n
n
Eg = 1.4 eV
Eg = 3.0 eV
Through the structure
engineering, polymers
with different emitting
colors were synthesized.
PPV
n
Eg = 2.4 eV
R1
O
R1
n
R2
Eg = 2.4 eV
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O
R2
n
Eg = 2.1 eV
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Delocalization of Charge Carriers in
Polyacetylene
Localized! Charge cannot go anywhere!!!
Delocalized! Charge carriers can move around!!!
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NCKU Institite of Electro-Optical
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Delocalization and Transport of Charge
Carriers
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Conjugated Polymers: Basic
Materials and Chemistry
• Conduction polymers:
Polyacetylene, Polyaniline, PEDOT/PSS… etc.
• Semiconducting polymers:
Polythiophenes, Oligothiophenes… etc.
• Light-emitting/Photovoltaic Polymers:
Poly-(para-phenylene-vinylene), Poly(paraphenylene), Polyfluorene… etc.
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Scientific Interest in Organic Materials
• 1950’s – steady work on crystalline organics starts
• 1970’s – organic photoconductors (Xerography)
• 1980’s – organic non-linear optical materials
• 1987 – Kodak first published the efficient organic light-emitting
devices (OLED)
• 1990 – Cambridge groups publish the first polymer light-emitting
diodes (PLED)
• Since then, the field has dramatically expanded both
commercially and scientifically, including OLED, PLED,
transistors, potovoltaic, solar cells………
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What are the OLEDs?
• Invented by Dr. Ching W Tang （鄧青雲博士）(kodak) 1987年
• OLED 全名叫做有機發光二極體 (Organic Light-Emitting Diode)
• 部分國外又稱 OEL為有機電激光顯示 (Organic Electroluminescence
Display)
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NCKU Institite of Electro-Optical
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OLED Basic Device Configuration
Double layers structure
• 電洞傳輸層-Hole
Transport (injection)
Layer (HTL)
• 電子傳輸層– Electron
Transport Layer (ETL)
• 發光層- Emitting Layer
(EML)
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First OLED Invented by Dr. Ching W Tang
(kodak) 1987
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Absorption, Fluorescence &
Phosphorescence Process
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Photophysics process
carrier separation
e-/h+
carrier injection
dissociation
recombination
dissociation
Intersystem crossing
Singlet excitons
T-T annihilation
Triplet excitons
fluorescence
hν1
phosphorescence
hν2
non-radiation
heat
ground state
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Operation of OLEDs
_
ETL
_ _ _ _ __ _ _
+ + + + + + ++
HTL
Anode
Cathode
+
ITO
Glass or PET substrate
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Electroluminescence of O/PLED
Single layer device
PLED
Double layer device
OLED
Double layer device
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Mechanism of Electroluminescence
hole (+)
+
electron (-)
exciton (*)
3 symmetric states
Triplets
+
or
sin
gle
t
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tri
ple
t
1/
+
2
1/
-
2
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1 antisymmetric state
Singlet
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Fluorescence and Phosphorescence
Singlet exciton
Intersystem crossing (ISC)
S1
Triplet exciton
T1
Fluorescence
Phosphorescence
25%
75%
S0
Ground state
Decay from singlet allowed by symmetry: fast and often efficient.
Decay from triplet disallowed by symmetry: slow and usually inefficient.
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Device preparation
ITO/Glass substrate
Vacuum<10-5 torr
Organic materials
Lecture note of Prof. Chou, NTU Phys.
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What are PLEDs?
• Invented by Richard. H. Friend (University of Cambridge,
Cavendish Laboratory) 1990年
• PLED 全名叫做高分子發光二極體 (Polymer Light-Emitting Diode)
• Usually for single layer device configuration
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First PLED Invented by Richard. H. Friend
(Cambridge University, Cavendish Laboratory)1990
They used Al as the cathode material at that time.
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Synthetic Route to PPV
J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend,
P. L. Burns, and A. B. Holmes, Nature, 347, 539 (1990).
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Schematic Energy Level Diagram
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Processing for the fabrication of a typical PLED
Pre-cleaned ITO/glass
substrate
O
Spin coating PEDOT
layer & baking
O
O
O
O
Cathode deposition
O
S
S
S
S
+
S
O
Spin coating MEH-PPV
layer & baking
O
O
O
n
MEH-PPV
O
*
n
m
n
SO3-
SO3H
O
PEDOT:PSS
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NCKU Institite of Electro-Optical
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*
Eg=2.1eV
Orange-red
or yellow
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PLED Devices at NCKU
Biased device
Before bias
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Why they are so important?
Self-luminescent
No viewing angle limitation
Thin, Light weight
Low operation voltage
Flexible substrate application
http://www.nobel.se/chemistry/laureates/2000/illpres/7.html
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NCKU Institite of Electro-Optical
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Recent progress of EL Panels
Ink-jet printed EL display, Toshiba and Epson 2002
20 inches, amorphous Si, active matrix, full color OLED display
WXGA (1280 x 768 pixels), 25 W, 300 cd/m2, CMO 03/12/2003
Kodak digital camera, available on April 2003
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NCKU Institite of Electro-Optical
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Reasons for organic solar cells
Organic solar cells: moderate
efficiencies and very low cost
Inorganic photovoltaic cell
T.-F. Guo
S.E. Shaheen,
D.S. Ginley, G.E. Jabbour, Mrs. NCKU
Bull., 30,Institite
pp.10- of Electro-Optical
Science & Engineering
18(2005).
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Flexible Donor-acceptor type solar cells
hν
A Flexible,
high efficiency
by SIMENS AG
T.-F.
Guo printed plastic solar cell withNCKU
Institite ofmade
Electro-Optical
Science & Engineering
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Working principle of organic solar cell
A Donor - Acceptor type bulk heterojunction solar cell
Metal electrode
Donor + Acceptor
ITO
hν
S
S
S
S
n/4
ehν
e-
Donor-P3HT
e+
ITO/PEDOT h
EF
h+
OCH2
Metal electrode
h+
O
h+
(Al, Ca/Al etc.)
Acceptor-PCBM
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NCKU Institite of Electro-Optical
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J (photo-current density) – V (Bias) curves for devices with Al and
Ca/Al as the cathodes
FF 
 power
VMPP  J MPP
Voc  J sc
Pout FF  J sc Voc


Pin
Pin
•Incident power of 90mW/cm2
Cathode
material
Voc(V)
Jsc(mA/cm2)
Vmpp(V)
Jmpp(mA/cm2)
Fill Factor
ηpower
Al
0.564
-8.153
0.426
-3.691
0.423
2.142%
Ca/Al
0.544
-12.933
0.382
-10.433
0.566
4.383%
Conclusions
• Organic electronics乃是一項跨領域的學科，
涵蓋半導體元件物理、基礎物理、電機、
化學、材料…而基礎物理化學的基礎更是
為重要。
• Flexible devices (軟性電子) 將是未來科技
的一項研究重點，此乃organic electronics
之發展強項。
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NCKU Institite of Electro-Optical
Science & Engineering
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Future of Information Display
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