A Model for Electric Characteristics of P3HT:PCBM Bulk Heterojunction Solar Cells
Khadije Khalili1, Hossein Movla2, Hamed Azari Najafabadi1
1 Research Institute for Applied Physics and Astronomy (RIAPA), University of Tabriz, Tabriz, Iran
2 Department of Solid State Physics, Faculty of Physics, University of Tabriz, Tabriz, Iran
RIAPA
NSSC902
☼ A short history of solar cells
☼ Polymer Solar Cell☺ Principle and device configuration
☼ Organic Solar Cell Materials ☼ The objectives of our work
☺ Electric characteristics☺ Results
☼ References
9/15/2011
Contents
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A short history of solar cells
First Generation - Single crystal silicon wafers (c-Si)
Second Generation - Amorphous silicon (a-Si) - Polycrystalline silicon (poly-Si) - Cadmium telluride (CdTe) - Copper indium gallium diselenide (CIGS) alloy
Third Generation - Nanocrystal solar cells - Photoelectrochemical (PEC) cells • Gräetzel cells - Polymer solar cells - Dye sensitized solar cell (DSSC)
Fourth Generation - Hybrid - inorganic crystals within a polymer matrix
Medium efficiency , but
expensive
Cheap , but low efficiencies
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Polymer Solar Cell Principle and device configuration:
Absorption of light
Exciton dissociation Double-layer device Bulk-heterojunction (BHJ)
Charge transportation
Li Gui, LU GuangHao, et al. Progress in polymer solar cell, Chinese Science Bulletin (2007)
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Organic Solar Cell Materials Most important Semiconducting polymers as
1- electron donor polymers: (MEH-PPV), (MDMOPPV), poly(3-hexeylthiophene) (P3HT),
(PFO- DBT), (PCDTBT), regioregular poly(3-hexeylthiophene) (RR-P3HT)
2- hole acceptor materials:fullerene (C60) 6,6-phenyl C61 -butyric acid methyl ester (PC61BM), 6,6-phenyl C71-butyric acid methyl ester
(PC71BM)
and photovoltaic devices are fabricated on cleaned glass substrates with a patterned ITO layer. Other common materials are consist of the conducting polymer poly-wethylene dioxy thiophenex:poly-wstyrene sulfonatex (PEDOT:PSS), the active layer (P3HT:PCBM), and aluminum electrodes are thermally evaporated.
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The objectives of our work are: We choose a polymer solar cell with P3HT:PCBM composite as
photoactive layer.
Considering Shottky contacts, barrier lowering due to the image potential, Langevin recombination, and field dependent mobility, we adopt the time-independent one-dimensional drift-diffusion model.
Using the boundary conditions at x=0 and x=d and this fact that , we solve Poisson’s equation and find expressions of current density equation, charge carrier distribution, and J-V characteristics.
By using calculated equations, we plot charge carrier density and the terminal current versus cell thickness with different applied voltage, from equilibrium to built-in voltage.
Finally, we compare our calculations for two thickness 100 and 200nm.
A. B. Walker, S. J. Martin, A. Kambili, J.Phys.: Condense. Matter 14, 9825(2002)
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Electric characteristics:)exp()0( 1
kTNn c
)exp()( 2
kTNdn c
1
21 )()(
xdeV
xeU
1 1
1
1
( ) ( )(exp[ ] exp[ ])( )( ) 1 exp[ ]( )exp( ) [exp( ) 1]
( )exp
bi bic
bi
bi
bic
eV e V V e V VNe V V xkT d dN x e V V kT d
kT kTe V V xNkT d kT
01 1
1
( ) ( )( )(exp[ ] exp[ ])
( )exp( ) [1 exp( )]
( )
bi bi sc bi s
bi s
sL
p
eV e V V e V V JARe N V V JARkT d dJ e V V JARdnkT
kT kTV JAR J VAR
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Results
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Fig 1. Variation in the band edge of the semiconductor in terms of the active region distance in thermal equilibrium for different donor like (n-type) dopings.
0 20 40 60 80 100-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Distance x (nm)
-qV
(x) (
eV)
Nd=1017
Nd=1016 2
1
Nd=1014
Nd=1015
0 50 100 150 200-2.5
-2
-1.5
-1
-0.5
0
0.5
1
Distance x (nm)
-qV
(x) (
eV)
Nd=1017
Nd=1016 2
1
Nd=1014
Nd=1015
100 nm
200 nm
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0 0.2 0.4 0.6 0.8 10.8
1
1.2
1.4
1.6
1.8
2x 10
-3
voltage (V)
elec
tron
mob
ility
(cm
2 /Vs)
Fig 2. Variation of electron mobility versus cell voltage.
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Fig 3. The injected electron profile in a semiconductor with cathode on the right hand side and anode on the left hand side. In the case of V=0 is thermal equilibrium.
0 50 100 150 20010
6
108
1010
1012
1014
1016
1018
Distance x (nm)
Cha
rge
Car
rier D
ensi
ty (c
m-3
)
V=0V=0.1V=0.2V=0.3V=0.4V=0.5
0 20 40 60 80 10010
6
108
1010
1012
1014
1016
1018
Distance x (nm)
Cha
rge
Car
rier D
ensi
ty (c
m-3)
V=0V=0.1V=0.2V=0.3V=0.4V=0.5 100 nm
200 nm
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0 20 40 60 80 1000
0.5
1
1.5
2
2.5
3x 10
-9
Distance x (nm)
Cur
rent
Den
sity
(mA
/cm2 )
DriftDiffusion
Fig 4. Diffusion and drift currents at 300 K in the double Schottky barrier device at 0.5 V. Diffusion current is larger than the drift current and the two currents flow in the opposite directions.
0 20 40 60 80 100 120 140 160 180 2000
0.2
0.4
0.6
0.8
1
1.2
1.4x 10
-9
Distance x (nm)
Cur
rent
Den
sity
(mA
/cm
2 )
DriftDiffusion
100 nm
200 nm
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-0.5 0 0.5 1-8
-6
-4
-2
0
2
4
6
J (m
A/c
m2 )
Voltage (V)
jillumination (jsc=40)
jillumination (jsc=60)
jillumination (jsc=80)
Jdark
Fig 5. Calculated l J-V characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell in dark and under different illumination intensities.
-0.5 0 0.5 1-8
-6
-4
-2
0
2
4
6
J (m
A/c
m2 )
Voltage (V)
jillumination (jsc=40)
jillumination (jsc=60)
jillumination (jsc=80)
Jdark
100 nm
200 nm
40 mw/cm2
60 mw/cm2
80 mw/cm2
40 mw/cm2
60 mw/cm2
80 mw/cm2
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-0.5 0 0.5 1-14
-12
-10
-8
-6
-4
-2
0
2
4
6J
(mA
/cm
2 )
Voltage (V)
JLamp
jillumination (jsc=40)
jillumination (jsc=60)
jillumination (jsc=80)
Jdark
Fig 7. Calculated J-V characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell in dark and under different illumination intensities. The dashed blue line is the Lampert et.al. calculated dark current.
40 mw/cm2
60 mw/cm2
80 mw/cm2
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-0.5 0 0.5 1-4
-3
-2
-1
0
1
2
3
4
5
6J
(mA
/cm
2 )
Voltage (V)
Jil, d=200 nm
Jil, d=100 nm
Fig 8. Calculated J-V characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell for different thickness.
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References
9/15/2011
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Appreciate for your interest