# Photovoltaic effect

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## Main Question or Discussion Point

Photons cause electrons to move to excited state.
In excited state in the conduction band, electrons are free to move through the material.
This motion of the electron creates an electric current in the cell.
But how far can electrons move? And because electrons are free to move in photovoltaic
cell ( panel), does it mean that mass of the photovoltaic cell ( panel) changes?

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ZapperZ
Staff Emeritus
Photons cause electrons to move to excited state.
In excited state in the conduction band, electrons are free to move through the material.
This motion of the electron creates an electric current in the cell.
But how far can electrons move? And because electrons are free to move in photovoltaic
cell ( panel), does it mean that mass of the photovoltaic cell ( panel) changes?
I am not sure you understand the physics of photovoltaic.

Please note that it isn't just about putting an electron in the conduction band of a semiconductor. That does nothing other than increasing its conductivity. There must be a potential difference being built up, because a "cell" is a battery that is a source of potential difference. This is why a photovoltaic cell usually consists of a pn-junction.

The question of "how far can electrons move" is puzzling, because this is no different than the usual electric current. Do you also wondered how far electrons move in a typical conductor when it is conducting electricity? It is NOT VERY FAR (ref: the Drude model). In fact the mean free path of electrons in a metal is typically LESS than the mean free path of electrons in the conduction band of a semiconductor mainly because the electron-electron scattering rate in a semiconductor is significantly less (there are fewer conduction electrons).

Other than that, I don't understand what you are trying to get at with your question.

Zz.

Thanks for answering. Can you please recommend a book/website where I can study more about the physics of photovoltaic ?

My favorite book about semiconductors is by Simon Sze, called "Physics of Semiconductor Devices".