Changes

== The Sun ==

== The Sun ==

The [[wikipedia:Sun|sun]] is the star at the center of the solar system, it has been shinning for more than 4-billion years. It is a nearly perfect sphere of hot plasma with internal convective motion that generates a magnetic field via a [[wikipedia:Solar_dynamo|dynamo]] process.  

{{#seo:|title=Photovoltaic Effect - Wikisolar|description=WikiSolar explain the Photovoltaic Effect|keywords=PV, photovoltaic, how does solar panels work,}}The [[wikipedia:Sun|sun]] is the star at the center of the solar system, it has been shinning for more than 4-billion years. It is a nearly perfect sphere of hot plasma with internal convective motion that generates a magnetic field via a [[wikipedia:Solar_dynamo|dynamo]] process.  

Some stars are enormous sources of X-rays; others mostly generate radio signals. The sun, while producing these and other energies, releases 95% of its output energy as light, some of which cannot be seen by the human eye.  

Some stars are enormous sources of X-rays; others mostly generate radio signals. The sun, while producing these and other energies, releases 95% of its output energy as light, some of which cannot be seen by the human eye.  

Different types of semiconductor have slightly different properties and lend themselves to different applications in various forms of semiconductor devices.

Different types of semiconductor have slightly different properties and lend themselves to different applications in various forms of semiconductor devices.

[[File:Semiconductor.png|center|thumb|508x508px]]

[[File:Semiconductor.png|center|thumb|508x508px|Example of semiconductor]]

=== The Silicon atom ===

=== The Silicon atom ===

The silicon atom has fourteen electrons arranged in such a way that the outer four can be given to, accepted from, or shared with another atom. These 4 outer electrons are called valence electrons, they have the highest energy state.  

The silicon atom has fourteen electrons arranged in such a way that the outer four can be given to, accepted from, or shared with another atom. These 4 outer electrons are called valence electrons, they have the highest energy state.  

[[File:Silicon atom.png|center|thumb|421x421px]]

[[File:Silicon atom.png|center|thumb|421x421px|Silicon atom structure]]

==== Merging the P-type semiconductor and the N-type semiconductor ====

==== Merging the P-type semiconductor and the N-type semiconductor ====

Now that we understand the concept of P and N type semiconductors, the concept of holes and electrons. Let us go one step further to merge the P-type and N-type and understand how electric fields are created.

Now that we understand the concept of P and N type semiconductors, the concept of holes and electrons. Let us go one step further to merge the P-type and N-type and understand how electric fields are created.

[[File:Diode PN junction.png|center|thumb]]

[[File:Diode PN junction.png|center|thumb]].[[File:PV effect 1.png|thumb|alt=|left|1. Electrons of N-type start to fill holes of the P-type]]

 

When the n and p materials are in contact, free electrons in the n-type material adjacent to the many holes in the p-type material at the junction will jump into the p-type material, filling the holes. This charge transference process happens rapidly along the dividing line (junction), sending huge numbers of electrons to 'the p-type side and holes to the n-type side.

When the n and p materials are in contact, free electrons in the n-type material adjacent to the many holes in the p-type material at the junction will jump into the p-type material, filling the holes. This charge transference process happens rapidly along the dividing line (junction), sending huge numbers of electrons to 'the p-type side and holes to the n-type side.

[[File:PV effect 3.png|thumb|alt=|left|3. Potential barriers when all electrons have filled holes and are now electrically stable]]

[[File:PV effect 3.png|thumb|alt=|left|3. Potential barriers when all electrons have filled holes and are now electrically stable]]

In other words, charged carriers that have already crossed the junction set up an electric force (field) that acts as a barrier opposing the further flow of free carriers. As more carriers cross the junction, the barrier enlarges, making it increasingly difficult for other carriers to cross. Eventually, an equilibrium is established where (statistically speaking) no more electrons or holes switch sides.

In other words, charged carriers that have already crossed the junction set up an electric force (field) that acts as a barrier opposing the further flow of free carriers. As more carriers cross the junction, the barrier enlarges, making it increasingly difficult for other carriers to cross. Eventually, an equilibrium is established where (statistically speaking) no more electrons or holes switch sides.

As the N-type material has lost electrons and the P-type has lost holes, the N-type material has become positive with respect to the P-type which has also turned negative.

As the N-type material has lost electrons and the P-type has lost holes, the N-type material has become positive with respect to the P-type which has also turned negative.

How then is the electric current generated ?

How then is the electric current generated ?

[[File:PV cell with photon.png|left|thumb|314x314px]]

[[File:PV cell with photon.png|left|thumb|314x314px]]

[[File:PV cell with photon inside.png|thumb|352x352px|alt=]]When sunlight or energy from the light (Photons, that has enough energy to free an electron from a bond in the silicon crystal) strikes the PV cell, and is absorbed by the semiconductor in the depletion zone.[[File:PV cell with photon and electron holes.png|left|thumb]]

[[File:PV cell with photon inside.png|thumb|352x352px|alt=]]

An electron hole pair is created, i.e a free electron and a free hole.  Because of the existing electric field at the depletion Zone, this freed electron is attracted to the n-type side, being repelled by the barrier. Likewise, the holes encounter is attracted to the p-type side.

.

Now what? The electrons and holes are free and excited with nowhere to go. The continual incident rays of the photons continue to generate electron hole pairs and charge separation causes the presence of uncombined excess negative charges on the n-type side and excess holes on the p-type side, a charge imbalance exists in the cell.

Now what? The electrons and holes are free and excited with nowhere to go. The continual incident rays of the photons continue to generate electron hole pairs and charge separation causes the presence of uncombined excess negative charges on the n-type side and excess holes on the p-type side, a charge imbalance exists in the cell.

          [[File:PV cell in circuit.png|left|thumb|350x350px]]  

 

 

Negative charges flow out of the electrode on the n-type side, through a load (such as a light bulb}, and perform useful work on that load (such as heating the light bulb's filament to incandescence}. The electrons then flow into the p-type side, where they recombine with holes near the electrode.[[File:PV cell in circuit.png|left|thumb|350x350px]]

If we then connect the n-type side to the p-type side of the cell by means of an external electric circuit, current flows through the circuit (which responds just as if powered by a battery} because this reduces the light induced charge imbalance in the cell.  

[[File:PV cell in circuit 3.png|thumb|350x350px|alt=]][[File:PV cell in circuit 2.png|thumb|351x351px|alt=|center]] 

Negative charges flow out of the electrode on the n-type side, through a load (such as a light bulb}, and perform useful work on that load (such as heating the light bulb's filament to incandescence}. The electrons then flow into the p-type side, where they recombine with holes near the electrode.

.  

[[File:PV cell in circuit 3.png|thumb|350x350px|alt=]][[File:PV cell in circuit 2.png|thumb|351x351px|alt=|center]]The light energy originally absorbed by the electrons is used up while the electrons power the external circuit. Thus, an equilibrium is maintained.  

The light energy originally absorbed by the electrons is used up while the electrons power the external circuit. Thus, an equilibrium is maintained.  

The incident light continually creates more electron-hole pairs and, thereby, more charge imbalance; the charge imbalance is relieved by the current, which gives up energy in performing work. The amount of light incident on the cell creates a near proportional amount of current.  

The incident light continually creates more electron-hole pairs and, thereby, more charge imbalance; the charge imbalance is relieved by the current, which gives up energy in performing work. The amount of light incident on the cell creates a near proportional amount of current.