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

NSSC903 9/15/2011

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.

NSSC9016

References

9/15/2011

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[12] W. U. Huynh, J. J. Dittmer, W. C. Libby, G. L. Whiting, A. P. Alivisatos, Adv.Funct.Mater. 13 (2003) 73[13] J.Y.Kim, K.Lee, N.E.Coates, D.Moses, T.Nguyen,M.Dante,A.J.Heeger, Efficient tandem polymer solar cells fabricated by all-solution processing, Science 317(2007) 222.[14] C. J. Brabec, N. S. Sariciftci, J. C. Hummelen, Adv. Func. Mater. 11 (2001) 15.[15] H. Hoppe, N. Arnold, D. Meisner and N. S. Saricirtci: Modeling the optical absorption whit in conjugated polymer/fullerene-based bulk heterojunction organic solar cells, Sol. Energy Mater. Sol. Cells. 80, 105 (2003)[16] P. Kumar, S. C. Jain, V. Kumar, S. Chand, R. P. Tandon, J. Appl. Phys. 105, 104507 (2009). [17] A. B. Walker, S. J. Martin, and A. Kambili, J. Phys.: Condens. Matter 14, 9825 (2002).[18] S. J. Martin, Alison B. Walker, A. J. Campbell and D. D. C. Bradley, J. Appl. Phys. 98, 063709 (2005). [19] V. D. Mihailetchi, P. W. M. Blom, J. C. Hummelen, and M. T. Rispens, J. Appl. Phys. 94, 6849 (2003).

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