Arno Smets

Working Principle of a Semiconductor Based Solar CellSemiconductor Junction II - The Solar Cell

Week 2.4.2

Semiconductor Junction – Thermal Equillibrium

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- - - -

- - - -

- - - -

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

n regionp region

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

No net current

Semiconductor Junction – Forward Bias

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+ + + +

+ + + +

+ + + +

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n regionp region

+ -Field reduced

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

Semiconductor Junction – Forward Bias

n regionp region

+ -Field reduced- - - -

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- - - -

- - - -

- - - -

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

Net current!

EF EF

driftdiffusion

driftdiffusion

EF

EF

driftdiffusion

driftdiffusion

EF

EF

driftdiffusion

driftdiffusion

EF

EF

driftdiffusion

driftdiffusion

qV

Semiconductor Junction – Reverse Bias

n regionp region

- +Field increased- - - -

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- - - -

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

Semiconductor Junction – Reverse Bias

n regionp region

- +Field increased- - - -

- - - -

- - - -

- - - -

- - - -

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

Extremely Small Net current!

Semiconductor Junction – under illumination

n regionp region

- - - -

- - - -

- - - -

- - - -

- - - -

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

Semiconductor Junction – under illumination

n regionp region

- - - -

- - - -

- - - -

- - - -

- - - -

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

Electron Diffusion Je = qDedn/dxElectron Drift Je = nqeE

Hole Drift Jh = pqhEHole Diffusion Jh = qDhdp/dx

Short Circuit

n regionp region

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+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

Open Circuit

n regionp region

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+ + + +

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+ + + +

V

E Field

p-n junction Solar Cells

Three essential steps required for the operation of a solar cell:

1. Generation of electron-hole pairs in the cell

2. Separation of electron and hole at the junction

3. Collection of electrons and holes at the terminals

Thank you for your attention!