Yan Us-china 2009
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Heterojunction effects in OPV cells Categories of heterojunctions OPV cells using WEG films Optimization towards smart cells
Donghang Yan ( 闫东航 ) State key laboratory of polymer physics and chemistry, Changchun Institute of Applied Chemistry, CAS, Renmin Str. 5625, Changchun 130022, China
H.B. Wang, D.H. Yan, Science in China B39, 1 (2009).
Categories of heterojunctions
Typical organic systems ZnPc/C60 CuPc/F16 CuPc, BP2T/F16 CuPc, P3HT/C60 F16 CuPc/SnCl2Pc p-6P/VOPc, p-6P/CuPc, 3PTh/VOPc
FET
-6
1.0x10
Gate-source voltage =0,-10V
Au
F16 CuPc CuPc
Au Au
+++
Ta2O5 Heavily doped silicon wafer
Normally-on OFET
Drain current (A)
0.0
-30V -50V
-6
-1.0x10
-6
-2.0x10
-6
-3.0x10
-6
-4.0x10
0V -10V -30V -50V
-50
CuPc/F16CuPc heterojunction CuPc single layer
-40 -30 -20 -10 Drain-source voltage (V)
Free holes accumulated at CuPc films
0
Semiconductor-Device Electronics, 1991 Oxford University Press
PN Junctions doping
n-type Si
Free e
p-type Si
Ion residual
Free h
No free e or h
E
Space charge region
- Diffusion theory
Organic PN Junctions
n-type Si
p-type Si E
- Diffusion theory
n-type F16 CuPc
E
p-type CuPc
- NEW theory ? !
D.H. Yan, H.B. Wang, B.X. Du, Introduction to Organic Semiconductor Heterojunctions, 2008
Thermal equilibrium conditions – a theoretical view 3.0
3.12
Energy (eV)
3. 5 4.0
6.0
3. 6
EFp 4.82
5.0
According to thermal equilibrium conditions, the electrons prefer to flow from the high energy work function position to low energy work function position when two semiconductors are brought into contact.
4.6 4.8
5.0 5.2
5.16
p-CuPc
6.1
EFn
p-Si
n-Si
6.3 6.66 n-F16 CuPc
C. Shen, A. Kahn, JAP90,4549,2001 H. Peisert et al, JAP 93, 9683 (2003). K.M. Lau et al, APL 88, 173513 (2006). A.Kahn, JAP. 86,4515,1999
Depletion HJ
HJ effects in typical OPV systems
Molecular model
Band model Working mechanism
OPV cells using WEG films Weak epitaxy growth
(Accumulation HJ) Mismatch of charge and exiton transport, is an intrinsic problem for OPV cells ?
Of MPc WEG films
• Depletion heterojunction with C60 Al EBL C60
WEG ZnPc Inducing layer ITO
• Space charge thickness ~ 40 nm • Charge carrier mobility as single crystal - No effective deep traps at RT - Shallow traps of 0.056 eV at low T • Exciton diffusion length should be longer
Glass
WEG films may over come the mismatch of charge/exiton transport in OPV cells
p-6P(2nm)
p-6P(2nm)/ZnPc(3nm)
N N N
N
N
p-6P
10µ mx10µ m p-6P(2nm)/ZnPc(30nm)
SiO2/ZnPc(30nm)
pp
RMS=0.8nm
RMS=2.4nm
N
Cu N N
CuPc
TFT transfer curves
Quality of WEG films is good as single crystal.
High quality of WEG films
No effective deep traps observed
VTFL
eNd 2 = 2ε
Density of deep traps is about 2.6× 1016 /cm3.
Deep traps dominates electrical behaviors of organic crystalline films.
Hall effect Lakeshore 7707, van der Pauw
delocalized transport
10:1
At the room temperature, the ratio of thermal activated charges to charges located at conductive band is ∼ 10 to 1 for WEG films.
Advanced Materials, adma.200903023, in press
OPV cells using WEG films •Planar heterojunction (PHJ) device
+
AM 1.5G
Cell structure
Voc (V)
Jsc
FF
PCE (%)
Saturation factor
(mA/cm2)
Ref PHJ
0.52
4.16
0.55
1.19
1.27
WEG PHJ
0.56
5.76
0.65
2.10
1.07
Free electrons and holes can be collected efficiently.
Exciton diffusion length of MPc WEG films
20nm<λ E< 40nm
Space charge field ~ 40nm
ZnPc WEG films
C60 films
Exciton diffusion length of WEG films is not longer enough.
• Planar-mixed heterojunction (PM-HJ) device
SF
High efficient cells are in optimization.
Optimization toward smart cells Larger VOC cell
(PCE 10%)
NIR cell
Performance ： Double Voc Tunnel junction
WEG sub cell 2
Connecting unit (Accumulation OHJ)
Connecting unit WEG sub cell 1
Outlooks • OHJ supplies a view angle to understand and develop OPV cells. • We realized WEG ZnPc films, and applied to OPV cells. - high charge carrier mobility, low deep traps - exciton diffusion length is comparable to the absorption - moderate efficiency • Potential space for improving efficiency of OPV cells, - NIR absorbing materials, and - smart tandem cells
Donghang Yan ( 闫东航 ) State key laboratory of polymer physics and chemistry, Changchun Institute of Applied Chemistry, CAS, Renmin Str. 5625, Changchun 130022, China
H.B. Wang, D.H. Yan, Science in China B39, 1 (2009).
Categories of heterojunctions
Typical organic systems ZnPc/C60 CuPc/F16 CuPc, BP2T/F16 CuPc, P3HT/C60 F16 CuPc/SnCl2Pc p-6P/VOPc, p-6P/CuPc, 3PTh/VOPc
FET
-6
1.0x10
Gate-source voltage =0,-10V
Au
F16 CuPc CuPc
Au Au
+++
Ta2O5 Heavily doped silicon wafer
Normally-on OFET
Drain current (A)
0.0
-30V -50V
-6
-1.0x10
-6
-2.0x10
-6
-3.0x10
-6
-4.0x10
0V -10V -30V -50V
-50
CuPc/F16CuPc heterojunction CuPc single layer
-40 -30 -20 -10 Drain-source voltage (V)
Free holes accumulated at CuPc films
0
Semiconductor-Device Electronics, 1991 Oxford University Press
PN Junctions doping
n-type Si
Free e
p-type Si
Ion residual
Free h
No free e or h
E
Space charge region
- Diffusion theory
Organic PN Junctions
n-type Si
p-type Si E
- Diffusion theory
n-type F16 CuPc
E
p-type CuPc
- NEW theory ? !
D.H. Yan, H.B. Wang, B.X. Du, Introduction to Organic Semiconductor Heterojunctions, 2008
Thermal equilibrium conditions – a theoretical view 3.0
3.12
Energy (eV)
3. 5 4.0
6.0
3. 6
EFp 4.82
5.0
According to thermal equilibrium conditions, the electrons prefer to flow from the high energy work function position to low energy work function position when two semiconductors are brought into contact.
4.6 4.8
5.0 5.2
5.16
p-CuPc
6.1
EFn
p-Si
n-Si
6.3 6.66 n-F16 CuPc
C. Shen, A. Kahn, JAP90,4549,2001 H. Peisert et al, JAP 93, 9683 (2003). K.M. Lau et al, APL 88, 173513 (2006). A.Kahn, JAP. 86,4515,1999
Depletion HJ
HJ effects in typical OPV systems
Molecular model
Band model Working mechanism
OPV cells using WEG films Weak epitaxy growth
(Accumulation HJ) Mismatch of charge and exiton transport, is an intrinsic problem for OPV cells ?
Of MPc WEG films
• Depletion heterojunction with C60 Al EBL C60
WEG ZnPc Inducing layer ITO
• Space charge thickness ~ 40 nm • Charge carrier mobility as single crystal - No effective deep traps at RT - Shallow traps of 0.056 eV at low T • Exciton diffusion length should be longer
Glass
WEG films may over come the mismatch of charge/exiton transport in OPV cells
p-6P(2nm)
p-6P(2nm)/ZnPc(3nm)
N N N
N
N
p-6P
10µ mx10µ m p-6P(2nm)/ZnPc(30nm)
SiO2/ZnPc(30nm)
pp
RMS=0.8nm
RMS=2.4nm
N
Cu N N
CuPc
TFT transfer curves
Quality of WEG films is good as single crystal.
High quality of WEG films
No effective deep traps observed
VTFL
eNd 2 = 2ε
Density of deep traps is about 2.6× 1016 /cm3.
Deep traps dominates electrical behaviors of organic crystalline films.
Hall effect Lakeshore 7707, van der Pauw
delocalized transport
10:1
At the room temperature, the ratio of thermal activated charges to charges located at conductive band is ∼ 10 to 1 for WEG films.
Advanced Materials, adma.200903023, in press
OPV cells using WEG films •Planar heterojunction (PHJ) device
+
AM 1.5G
Cell structure
Voc (V)
Jsc
FF
PCE (%)
Saturation factor
(mA/cm2)
Ref PHJ
0.52
4.16
0.55
1.19
1.27
WEG PHJ
0.56
5.76
0.65
2.10
1.07
Free electrons and holes can be collected efficiently.
Exciton diffusion length of MPc WEG films
20nm<λ E< 40nm
Space charge field ~ 40nm
ZnPc WEG films
C60 films
Exciton diffusion length of WEG films is not longer enough.
• Planar-mixed heterojunction (PM-HJ) device
SF
High efficient cells are in optimization.
Optimization toward smart cells Larger VOC cell
(PCE 10%)
NIR cell
Performance ： Double Voc Tunnel junction
WEG sub cell 2
Connecting unit (Accumulation OHJ)
Connecting unit WEG sub cell 1
Outlooks • OHJ supplies a view angle to understand and develop OPV cells. • We realized WEG ZnPc films, and applied to OPV cells. - high charge carrier mobility, low deep traps - exciton diffusion length is comparable to the absorption - moderate efficiency • Potential space for improving efficiency of OPV cells, - NIR absorbing materials, and - smart tandem cells
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