Nanostructured Polymer Solar Cells
D. Xi, C. Shi, Y. Yao, Y. Yang, Q. PeiMaterials Science and EngineeringCalifornia NanoSystems InstituteUniversity of California, Los Angeles [email protected]
2008 IEEE INTERNATIONAL RELIABILITY PHYSICS SYMPOSIUM
April 29, 2008
Soft Materials Research Lab
Polymer Solar Cell
Efficiency of inorganic solar cells: ~10–20%– Current Polymer Solar Cell: ~5%– Max Inorganic: ~40%
No clean room or high T steps needed (large-area, low cost) Flexible panels (form factor) Versatility of polymer structure and property via synthesis Nanostructural tailoring
Konarka
Soft Materials Research Lab
How Does It Work?
Yu, Heeger, et al, Science, 270, 1789(1995)
Soft Materials Research Lab
Mechanism and Efficiency
ηIQE = ηA × ηED × ηCT × ηCCStephen R. Forrest, MRS Bulletin, 30 (2005) p.28
VOC = LUMO – HOMO – Exiton binding )
Soft Materials Research Lab
Mechanism and Efficiency
Stephen R. Forrest, MRS Bulletin, 30 (2005) p.28-32
RSH = Shunt resistance (quality of diode)RS = Series resistance (quality of contacts & transport in bulk of film)
OC SC
in
V I FFPCE
P
Soft Materials Research Lab
Main Factors Limiting the Efficiency: Low absorption
H. Hoppe & NS Sariciftci, J. Mater. Res., Vol. 19, 1926 (2004)
Soft Materials Research Lab
Main Factors Limiting the Efficiency: Short Exiton Lifetime
A. Haugeneder, et al, Phys. Rev. B, 59(23), 15346: 1999T. Stubinger and W. Brutting, J. APPL. PHYS., 90(7), 3632: 2001
Exciton diffusion length in ordered polymers is 5-14 nm
n
p+-+-+-
n
p+-+-+-
Soft Materials Research Lab
Bulk Heterojunction in Polymer Blend
Donor/Acceptor Blend (100+ nm)
ITO
Al
hν
N.S. Sariciftci, Heeger, et al.
S. Forrest, et al.
Soft Materials Research Lab
Bulk Heterojunction
Stalmach U. et al, J. Am. Chem. Soc.,122, 5464 (2000)
Inganäs, et al, Adv. Mater., 13, 1871: 2001
Soft Materials Research Lab
Alkoxythiophene polymers?
S**
S
O
**
FETsSolar cells
??
Alkoxy PPV(MEH-PPV)
O
O
**
**
Alkyl PPV
P3HT+PCBM (200nm)
Alkoxy to alkyl:• Larger bandgap• Lower mobility• Less stable
Soft Materials Research Lab
Synthesis of regioregular polymers and copolymers
S
OC10H21
BrBrCH3MgBr
SBrBrMg
OC10H21
S
OC10H21
nreflux, THF
Ni(dppp)Cl2
1 2reflux P3DOT
S
OC10H21
BrBr
1
+S
C8H17
BrBrCH3MgBr
reflux, THF SBrBrMg
OC10H21
2
+S
BrBrMg
C8H17
4
Ni(dppp)Cl2
refluxS
OC10H21
*b
POT-co-DOT
S
C8H17
*a
3
S
OC10H21
BrMg/THF
30~50 C S
OC10H21
MgBr
NS
N
BrBr
Ni(dppp)Cl2/THF & reflux
NS
N
SS BrBr
OC10H21 OC10H21
BB+
C8H17C8H17 C8H17C8H17
NS
NS S
OC10H21OC10H21
n
Pd(Pph3)4/Toluene
K2CO3/H2O
PF-co-DTB
NS
N
SS
OC10H21 OC10H21
NS
NSS BrBr
OC10H21 OC10H21
NBS
5 67
8 7
O
OO
O
Shi, et al., J. AM. CHEM. SOC. 2006, 128, 8980-8986
Soft Materials Research Lab
UV-Vis-NIR of spin-coated films
300 400 500 600 700 800 9000.0
0.2
0.4
0.6
0.8
1.0
N
orm
aliz
ed A
bsor
banc
e
Wavelength (nm)
P3DOT POT-co-DOT PF-co-DTB P3HT P3OOT
d
X
X
X
X
X
X
X
X
X
O
OO
O
O
O
O
O
O
OO
O
X
Soft Materials Research Lab
-8
-7
-6
-5
-4
-3
-2
eV P3HT
Energy Levels of Semiconductors
Ca
PCBM
ITO
P3DOT
Al PF-co-DTB
POT-co-DOT
1.92eV1.78eV
1.64eV
P3OOT
1.91eV1.60eV
Soft Materials Research Lab
Solar Cell Structure
ITO/Glass
PEDOT:PSS (25 nm)
Polymer/PCBM (80-100 nm)
LiF (1 nm)
Al (80 nm)A
Soft Materials Research Lab
Characteristics of Bulk Heterojunction Cells
(AM 1.5G irradiation at 100 mW/cm2).
Polymer Polymer:PCBM Jsc Voc (V) FF (%) PCE (%) (w/w ratio) (mA/cm2)
P3DOT 1:1 0.14 0.02 26.5 0.0007
POT-co-DOT 1:1 0.60 0.22 41.2 0.054
PF-co-DTB 2:1 0.74 0.83 25.5 0.16
PF-co-DTB 1:1 2.92 0.78 32.8 0.74
PF-co-DTB 1:2 4.00 0.76 44.6 1.27
PF-co-DTB 1:4 4.31 0.76 48.6 1.60
Soft Materials Research Lab
IPCE plot of PF-co-DTB/PCBM (1:4) BH cells
400 500 600 700 8000
5
10
15
20
25
30
35
EQE
(%)
Wavelength (nm)
EQE (%)
Shi, et al., J. AM. CHEM. SOC. 2006, 128, 8980-8986
Soft Materials Research Lab
C60 PCBM vs C70 PCBM
300 400 500 600 700 8000.00.10.20.30.40.50.60.70.80.91.0
[60]PCBM [70]PCBM
[60]PCBM soltuion
[70]PCBM solution
Abso
rptio
n [a
.u.]
wavelength [nm]
Y. Yan, et al., APL 89, 153507 (2006)
Soft Materials Research Lab
Absorption of PF-co-DTB/[70]PCBM blends
Y. Yan, et al., APL 89, 153507 (2006)
Soft Materials Research Lab
AFM of PF-co-DTB/PCBM blends
Tapping mode Phase mode
PF-co-DTB: 1[60]PCBM: 4
PF-co-DTB: 1[70]PCBM: 4
Soft Materials Research Lab
Cell performance vs. PCBM concentration
0
1
2
3
4
5
6
7
25
30
35
40
45
50
55
60
30 40 50 60 70 80 900.0
0.5
1.0
1.5
2.0
2.5
30 40 50 60 70 80 900.72
0.74
0.76
0.78
0.80
0.82
0.84
Polymer: [60]PCBM Polymer: [70]PCBM
Jsc (
mA cm
-2 )
FF (%
)
weight percentage acceptor [wt.-%]
PCE
(%)
Voc (
V)
weight percentage acceptor [wt.-%]
Soft Materials Research Lab
IV Characteristics of polymer/PCBM BH cells
0.0 0.2 0.4 0.6 0.8 1.0-7
-6
-5
-4
-3
-2
-1
0
1Cu
rrent
Den
sity (
mA/
cm2 )
Voltage (V)
Polymer: [60] PCBM = 1:4 Polymer: [70] PCBM = 1:4
Soft Materials Research Lab
EQE of polymer/PCBM BH cells
300 400 500 600 700 8000
10
20
30
40
50
60 Polymer: [60]PCBM =1:4 Polymer: [70]PCBM =1:4
EQE
(%)
wavelength [nm]
Y. Yan, et al. APL 89, 153507 (2006)
Soft Materials Research Lab
Other Small Eg Polymers
P1 P7 P8 P5 P6 P9 P0 P2 P3 P4-5.6
-5.2
-4.8
-4.4
-4.0
-3.6
-3.2
-2.8
-5.06 -5.1-4.92
-4.64
-5.36-5.52
-5.1 -5.02
-4.47 -4.55
-3.29 -3.32-3.14
-3.3-3.1
-3.6-3.7
-3.25
-2.87 -2.91 LUMO HOMO
Ener
gy le
vel (
eV)
Polymer type
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Bulk Heterojunction in Nanorod/Polymer Blend
7nmx7nm
7nmx60nm(Huynh W.U., Science 295,2425, 2002)
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Bulk Heterojunction in Porous TiO2 / Polymer
Sintering TiO2 nanocrystals + P3HT
Quantum efficiency only 6%Due to incomplete filling and random distributed inferface
Well ordered 8nm pore TiO2 film + P3HT
Incomplete PL quench due to twist of polymer into 8nm pores;optimized infiltration depth 20nm, QE, 10%, power efficiency 0.45%
(Kevin M. Coakley, Adv. Funct. Mat 13, 301, 2003)
Soft Materials Research Lab
Bulk Heterojunction Based on CuPc Nanowires
ITO / CuPc / PTCBI / BCP / Ag
Power efficiency 2.7%
(Fan Y., Nature Materials 4, 37, 2005)
CuPc nanowires by CVD. Scale bar: 500 nm
PCE
FF
Voc
Soft Materials Research Lab
Interdigitated p-n Nanohybrid
transparent electrode
top electrode Au
p-Conjugated polymer
n-semiconductor
ITO/PEDOT
Diameter ~20nm, Height ~200nm Space between rods ~20nm
Two bicontinuous phases, effectively split exciton before recombination
Carriers have straight pathway to electrodesPrevent holes from reaching the negative
electrode and electrons from positive electrodes
Soft Materials Research Lab
Interdigitated p-n Nanohybrid: Polymer nanotube array
a
b
c
d
e
b
100 nm
1 m
500 nm
Xi et al. Nanotechnology 18 (2007) 095602
Soft Materials Research Lab
Interdigitated p-n Nanohybrid: CdS Nanorod array
CdS + PT by electropolymn CdS + P3HT by infiltration
500 nm
Soft Materials Research Lab
Summary
• Alkoxythiophene is a useful building block for highly-conjugated, low bandgap (co)polymers.
• BH solar cells based on PF-co-DTB and [70]PCBM: Jsc: 6.34mA/cm2Voc: 0.76VFF: 50.5% PCE: 2.4%
• More work is needed to improve mobility and band edge matching (PF-co-DTB: h = 2x10-5cm2/Vs)
• Interdigitated p-n nanohybrid is a good architecture but challenging to fabricate perfect nanostructure/material