Changes

Not all of the direct sunlight incident on earth's atmosphere arrives at the earth's surface as shown below.

Not all of the direct sunlight incident on earth's atmosphere arrives at the earth's surface as shown below.

[[File:Earth energy budget.png|center|thumb|632x632px|Source: NASA Atmospheric Science Data Center.]]

[[File:Earth energy budget.png|center|thumb|632x632px|Source: NASA Atmospheric Science Data Center.]]

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]]

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]]

As previously indicated, silicon has 4 valence electrons in its outer shell, all of which are normally part of bonds in a silicon crystal. Suppose by some means we introduce an '''impurity''' into an otherwise pure silicon crystal by '''substituting for a silicon atom an atom such as phosphorus''', or antimony '''having 5 valence electrons.'''

As previously indicated, silicon has 4 valence electrons in its outer shell, all of which are normally part of bonds in a silicon crystal. Suppose by some means we introduce an '''impurity''' into an otherwise pure silicon crystal by '''substituting for a silicon atom an atom such as phosphorus''', or antimony '''having 5 valence electrons.'''

[[File:N type semiconductor.png|center|thumb|421x421px]]

[[File:N type semiconductor.png|center|thumb|421x421px]]

The second type of an appropriately altered material can be formed '''by substituting into the silicon crystal, impurity atoms with one fewer valence electron than silicon'''. An impurity atom with three valence electrons (such as boron) would sit in the position of the original silicon atom, but one of its bonds with the silicon would be missing an electron, i.e., there would be a hole.  

The second type of an appropriately altered material can be formed '''by substituting into the silicon crystal, impurity atoms with one fewer valence electron than silicon'''. An impurity atom with three valence electrons (such as boron) would sit in the position of the original silicon atom, but one of its bonds with the silicon would be missing an electron, i.e., there would be a hole.  

[[File:P type semiconductor.png|center|thumb|400x400px]]

[[File:P type semiconductor.png|center|thumb|400x400px]]

==== 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:PV effect 1.png|center|thumb]]

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

 

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 2.png|none|thumb]]

[[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|none|thumb]]

[[File:PV effect 4.png|thumb|alt=|4. Depletion zone of a PN junction]]

 

 

This process continues back and forth until the number of electrons which have crossed the junction have a large enough electrical charge to repel or prevent any more charge carriers from crossing over the junction. Eventually a state of equilibrium will occur producing a '''“potential barrier”''' zone around the area of the junction as the donor atoms repel the holes and the acceptor atoms repel the electrons.

This process continues back and forth until the number of electrons which have crossed the junction have a large enough electrical charge to repel or prevent any more charge carriers from crossing over the junction. Eventually a state of equilibrium will occur producing a '''“potential barrier”''' zone around the area of the junction as the donor atoms repel the holes and the acceptor atoms repel the electrons.

Since no free charge carriers can rest in a position where there is a potential barrier, the regions on either sides of the junction now become completely depleted of any more free carriers in comparison to the N and P type materials further away from the junction. This zone around the '''PN Junction''' is now called the '''Depletion''' Layer.

Since no free charge carriers can rest in a position where there is a potential barrier, the regions on either sides of the junction now become completely depleted of any more free carriers in comparison to the N and P type materials further away from the junction. This zone around the '''PN Junction''' is now called the '''Depletion''' Layer.

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.

[[File:PV effect 6.png|none|thumb]]

[[File:PV effect 6.png|thumb|alt=|center]]

==== Generating current with Photons. ====

==== Generating current with Photons ====

Now that we understand the concept of depletion layer and the electric field generated. We now represent this basic diode form in the normal way a PV module was created.

Now that we understand the concept of depletion layer and the electric field generated, we now represent this basic diode form in the normal way a PV module was created :

[[File:PV effect 6ok.png|center|thumb]]

[[File:PV effect current.png|thumb|alt=|306x306px]][[File:PV effect 6ok.png|center|thumb|alt=|365x365px|Structure of a PV cell]]How then is the electric current generated ?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 effect current.png|none|thumb]]

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

[[File:PV cell with photon inside.png|center|thumb|342x342px]]

[[File:PV cell with photon and electron holes.png|left|thumb]]

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 in circuit.png|left|thumb|375x375px]]

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.

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.

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.  

And that is the photo-voltaic effect, a work coined from “'''photo'''” with the Greek '''meaning light''' and “voltaic” '''meaning''' voltage.

And that is the photo-voltaic effect, a work coined from “'''photo'''” with the Greek '''meaning light''' and “voltaic” '''meaning''' voltage.

== References & Videos ==

== References & Videos ==