BY Mohammad Wahiduzzaman Khan

Tanmoy Das GuptaAnd

Samia Subrina

p-i-n Solar Cell Modeling with Graphene as

Electrode

OUTLINE

• Theory of Solar Cell• Graphene • Graphene as Electrode• Model of Solar Cell with

Graphene as Electrode• J-V Characteristics• Comparative Study

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Theory of Solar Cell• Converts the incident solar

radiation energy into electrical energy

• Incident photons are absorbed to photo-generate charge carriers

• Illumination is given through the thin n-side

• The built-in field separates EHPs photo-generated in the depletion region

• EHPs further away from depletion region by minority carrier diffusion length are lost by recombination

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Theory of Solar Cell

PN Semiconductor Solar Cell PIN Semiconductor Solar Cell

PIN Solar Cell is more efficient as the depletion region here is wider and more

carriers are generated and drifted

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Theory of Solar Cell¿

Jph= Photo-current DensityJo= Reverse Saturation Current DensityV= Bias Voltagen= Ideality factork= Boltzman ConstantT= Absolute Temperate

h𝐽𝑝 =𝑞𝐺𝑜𝛼

¿

J-V Characteristic of Solar Cell5

ln & lp are minority carrier diffusion length for electrons and holes Go= Carrier generation at the top surface= Absorption Coefficientq= Charge of Electron

Solar Cell Electrode• The back electrode can be metallic

(opaque)• But the front electrode must be transparent

in order to let the incident photons pass through it

• Electrodes must present with minimum series resistance

• Previously metallic finger electrodes were used

• Now Indium-Tin-Oxide (ITO) is used widely as transparent electrode

• Graphene is a material with the potential to replace ITO as the solar front electrode

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Graphene

2D Carbon Sheet (only one atom thick = 0.35nm) Hexagonal Crystal Structure Zero bandgap Semiconductor or zero overlap Metal (tunable 0-

0.25eV) High metallic strength (few hundred times stronger than steel) Flexible High Thermal Conductivity (K= 5,000 W / m.K ) Excellent Electron Mobility (as high as 20,000 sq cm / V.s) High Intrinsic Carrier Concentration (1012 cm-2 sheet density) High Transparency (upto 98%)

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Graphene vs ITO• ITO is more costly and the

world supply is expected to be depleted by 2017

• The production process of Graphene has been improving and becoming cheaper

• ITO is rigid and fragile • Graphene is flexible and

mechanically strong. So it can be incorporated with flexible solar cell

• Transparency of ITO is around 85%

• Graphene shows more transparency than ITO

• ITO has a mobility of upto 70 cm2/V.s

• Graphene has a mobility of upto 20,000 cm2/V.s

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• Another material with the potential of being used as

the electrode of solar cell is Carbon Nanotube (CNT)

• It is a one dimensional (1D) material ;

Graphene can be rolled in to make CNT

• It has a transparency of around 90%

• Its mobility is also very high (as high as 79,000cm2/V.s)

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CNT

Graphene as Electrode

All the properties of Graphene makes it extremely suitable for its use as the front

electrode of solar cell.

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Physics

. v Dn nD n n

q

nJ

E

p pD p pq

pJ

E

Drift-Diffusion EquationPoisson’s Equation11

Where, D = Electrical Displacement Field

= Free Charge Density

Where, n & p are concentration

are current density

Dn and Dp are diffusion coefficient, µn and µp are mobility

of electrons and holes respectively

Geometry

(47nm)p-Si

(30nm)n-Si

i-Si (250nm)

ContactGraphene

(1nm)

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Sample Doping Profile

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0.0 0.1 0.2 0.3 0.4 0.5-450-400-350-300-250-200-150-100-50

050

100

Current Density (A/m

2)

Voltage (V)

J-V Characteristic of PIN Solar Cell with Graphene

Jph 378.5 A/m^2

Voc 0.4147 V

FF 76.45%

Eff 12 %

0.00 0.25 0.50

-400

-300

-200

-100

0

100

cSi aSi

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J-V Characteristic with Intrinsic Layer Variation

0.0 0.1 0.2 0.3 0.4 0.5-500-450-400-350-300-250-200-150-100-50

050

Current Density (A/m2)

Voltage (V)

0.25m

0.19m

0.09m PN

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J-V Characteristic with Intensity Variation

0.0 0.1 0.2 0.3 0.4 0.5

-4000-3500-3000-2500-2000-1500-1000-500

0500

100015002000

Current Density (A/m

2)

Voltage (V)

100 W/m2

1,000 W/m2

10,000 W/m2

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J-V Characteristic with Wavelength Variation

0.0 0.1 0.2 0.3 0.4 0.5-500-450-400-350-300-250-200-150-100-50

050

Current Density (A/m2 )

Voltage (V)

400nm 470nm 530nm 600nm

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Ref: Reporting solar cell efficiencies in Solar Energy Materialsand Solar Cells; Solar Energy Materials & Solar Cells 92 (2008) 371–373

Theoretical MeasurementIn our base design:

• The incident optical power, Pin = 1000 W/m2

• Wavelength of photon, = 530nm• Absorption Coefficient, = 1.58x 107m-1

• Generation, G = :: Beer-Lambart Equation• Photo-current density, = 415 A/m2

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Graphene vs ITO vs CNT

0.0 0.1 0.2 0.3 0.4 0.5-450

-400

-350

-300

-250

-200

-150

-100

-50

0

50

Current Density (A/m2)

Voltage (V)

ITO CNT Graphene

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Graphene vs ITO vs CNT

Performance indices Graphene CNT ITO

Jph (A/m2) 378.5 349.5 339.3

Voc (V) 0.4147 0.4135 0.4076

FF 76.45% 75.72% 68.23%

Eff 12% 10.9% 9.4%

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THANKYOU

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