The 4th U.S.-Korea NanoForum
April 26-27, 2007, Honolulu, USA
Improvement of Device Efficiency in
Conjugated Polymer/Fullerene NanoComposite Solar Cells
School of Semiconductor & Chemical Engineering
*
Chonbuk National University, Korea
Soo-Hyoung Lee
S
*
S
*
*
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Organic Solar Cells
All Organic solar cell
Dye-sensitized solar cell
e–
e–
LUMO
LUMO
HOMO
h+
HOMO
Electron Electron
Anode Donor Acceptor Cathode
τinj
CB
Cathode
τc
c
D*/D+
τr
Vo
surface
states
Electron Acceptor
c
Electron Donor
Anode
Substrate
I3/I
D/D
+
VB
TiO2
Dye
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
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All organic solar cells
Type of Active Layer
Material
Low Molecules
Cathode
Structure
D/A Heterojunction
Electron Acceptor
Electron Donor
Substrate
Anode
Double Active Layer
e–
e–
LUMO
Polymers
LUMO
D/A Bulk Heterojunction
HOMO
h
Anode
+
HOMO
Electron Electron
Cathode
Donor Acceptor
(p)
(n)
Single Active Layer
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Polymer-Fullerene Solar Cell
Host matrix morphology effect
Eff = 2.5 % @ 80 mW / cm2
Sean E. Shaheen, et al., Appl. Phys. Lett. 78, 841 (2001)
Toluene
Chlorobenzene
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
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Polymer-Fullerene Solar Cell
w/o Annealing
70oC
150oC
ITO / PEDOT / P3HT:PCBM / Al
Eff = 5 % @ 80 mW / cm2
(Annealing after Al deposition 150oC for 30 mins)
Heeger et al., Adv. Funct. Mater., 15, 1617 (2005)
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Polymer-Fullerene Solar Cell
™ Total thickness of active layer : < 100-150 nm
D/A Bulk Heterojunction (Single layer)
™ Maximum Efficiency: ~ 5 %
™ Nano-composited interpenentrating
network (IPN) structure
™ Photoinduced charge generation
in a 3D-network interfaces
™ D/A Bulk-heterojuction (BHJ):
¾ Electron-donor (p-type):
conjugated polymers
¾ Electron-acceptor (n-type):
Electron
fullerene (derivatives)
e–
e–
LUMO
transfer from
Polymer to C60 occurs
in a pico-second (<10-12)
LUMO
HOMO
h+
Anode
HOMO
Electron Electron
Cathode
Donor Acceptor
(p)
(n)
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
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Polymer-Fullerene Solar Cell
How to make efficiency improvements?
D/A Bulk Heterojunction
High
EFF
Materials
High
Jsc
Voc
FF
p-type
n-type
Nano-composited IPN structure
High
Absorption
Separation
Transportation
Interface control of
organic/metal
p-type
Devices
Structure
Bandgap (Eg)
HOMO & LUMO Mechanism Treatment
Additives
Crystallinity
ETC…
ETC…
n-type Cathode
Anode
Effective charge transportiation / collection
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Approach # 1
Efficient solar cells with interlayer
Interlayer (~10 nm): blocking of
electron & exciton from active layer
D/A Bulk Heterojunction
2.97
p-type
3.7
n-type
p-type
4.8
ITO
Active
4.2
5.2
PEDOT
5.33
Al
n-type
MDMO-PPV
6.1
PEDOT:PSS
Interlayer
PCBM
O
O
S
S
+
O
O
SO3-
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Approach # 1
Efficient solar cells with interlayer
1.5
1.0
Dark
2
Current( mA/cm )
0.5
0.0
-0.5
-1.0
-1.5
Photo
-2.0
without interlayer
with interlayer
-2.5
-3.0
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Bias (V)
Voc(V)
Jsc(mA/cm2)
FF
EFF(%)
without
interlayer
0.72
-1.062
0.301
0.229
with
interlayer
0.73
-1.940
0.409
0.583
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Approach # 2
Use of Triplet (Phosphorescence) Organic Materials
¾ Conventional polymer-fullerene organic solar cell (PPV-PCBM system)
+ SM Red-Dopant
MDMO – PPV : p-type material
PCBM : n-type material
Red-Dopant : absorber & ET (long lifetime)
2.97
3.7
4.2
4.8
Red-Dopant
(Phosphorescence)
ITO
Al
5.2
PEDOT
5.33
MDMO-PPV
6.1
PCBM
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Approach # 2
Use of Triplet (Phosphorescence) Organic Materials
• Power-conversion efficiency ≡ Light absorption ≡ Thickness of organic layer
∉ Exciton diffusion length (10-30 nm @ organic)
• Exciton diffusion length = Mobility × Lifetime
• Triplet (phosporescence) organic materials have “long exciton lifetime ≥ µS “
(fluorescence material: ≤ nS)
-2
w/o RD
- Singlet
- Triplet
w/ RD
-3
Al
Al
eISC
-4
hν
-5
○
ITO
MDMO-PPV
○
ITO
PCBM
Red Dopant
-6eV
ITO
MDMO Red Dopant
-PPV
PCBM
Al
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
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Approach # 2
Use of Triplet (Phosphorescence) Organic Materials
¾ Energy Transfer in PL measurement ¾ Photocurrent generation
(MDMO-PPV & Red Dopant)
(MDMO-PPV & Red Dopant)
1400
MDMO-PPV
Red Dopant
PPV + RD 5%
PPV + RD 10%
PPV + RD 15%
1000
-6
3x10
Photocurrent (arb, unit)
PL intensity (A.U.))
1200
800
600
400
2
1
MDMO-PPV:PCBM
MDMO-PPV:PCBM(1:2)
MDMO-PPV:PCBM:R-Dopant
MDMO-PPV:PCBM(1:2):TER002(10%)
200
0
550
600
650
700
Wavelength(nm)
750
800
0
400
600
800
Wavelength (nm)
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
1000
Approach # 2
Use of Triplet (Phosphorescence) Organic Materials
¾ Device Performances
ITO/ PEDT:PSS/ MDMO-PPV : PCBM/ LiF/ Al
ITO/ PEDT:PSS/ MDMO-PPV : PCBM : R-Dopant / LiF/ Al
100
40
480nm
MDMO-PPV:PCBM(1:2)
MDMO-PPV:PCBM
MDMO-PPV:PCBM(1:2):R-Dopant(10%)
MDMO-PPV:PCBM:R-Dopant
74.2mW/cm2
MDMO-PPV:PCBM(1:2)
MDMO-PPV:PCBM
MDMO-PPV:PCBM(1:2):R-Dopant(10%)
MDMO-PPV:PCBM:R-Dopant
Current (x10 A)
-6
-6
Current (x10 A)
50
20
0
-1.0
-0.5
0.0
Voltage (V)
0.5
1.0
0
-50
-1.0
-0.5
0.0
Voltage (V)
0.5
1.0
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
Approach # 2
Use of Triplet (Phosphorescence) Organic Materials
Voc (V)
Jsc(mA/cm2)
FF
EFF(%)
IPCE(%)
36.81
ITO/ PEDT:PSS/ MDMO-PPV : PCBM/ LiF/ Al
480nm(2.4mW/cm2)
0.8
0.4
0.44
4.97
74.2mW/cm2
0.85
2.62
0.42
1.28
ITO/ PEDT:PSS/ MDMO-PPV : PCBM : R-Dopant / LiF/ Al
480nm(2.4mW/cm2)
0.8
0.64
0.46
8.25
74.2mW/cm2
0.85
3.64
0.41
1.72
58.68
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University
More Questions or Discussion ?
Welcome !!
Thank you !!
Chonbuk National University
Soo-Hyoung Lee, Ph.D.
Professor
School of Semiconductor & Chemical Engineering
Chonbuk National University
664-14 Duckjin-dong, Jeonju, 561-756, Korea
063-270-2435 / 011-9960-9363 (Phone)
063-270-2306 (Fax)
[email protected]
Organic
Organic Optoelectronic
Optoelectronic Materials
Materials Lab
Lab // Chonbuk
Chonbuk National
National University
University