doping silicone

ws9876
ws9876 Solar Expert Posts: 448 ✭✭✭
in General Solar Power Topics #1
silicone is coated with other elements to make a pn jct. are both sides of silicone doped or only one? explain...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: doping silicone

    I am not sure how deep you want to go, but this link has a high level view of the process:

    http://www.solarworld-usa.com/solar-101/making-solar-panels
    Diffusing
    Next, wafers are moved in cartridges into long, cylindrical, ovenlike chambers in which phosphorus is diffused into a thin layer of the wafer surface. The molecular-level impregnation occurs as the wafer surface is exposed to phosphorus gas at a high heat, a step that gives the surface a negative potential electrical orientation. The combination of that layer and the boron-doped layer below creates a positive-negative, or P/N, junction – a critical partition in the functioning of a PV cell.

    In this example, the silicon ingot is made with Boron--So the whole ingot (and sliced into cells) is "P type" material. The above diffusion process makes the "N type" silicon on one side of the cell. Where the diffusion "stops" is the P/N junction.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #3
    Re: doping silicone
    ws9876 wrote: »
    silicone is coated with other elements to make a pn jct. are both sides of silicone doped or only one? explain...
    In the first place, it's silicon, not silicone. There is a great deal of difference. One is a crystalline substance from which electrical devices are made, the other is what gives many pole dancers that extra jiggle.

    Doping of silicon is not a coating but an infusion. Depending on the doping concentration, the doping substance, and the layer thickness, silicon can be doped in a number of ways: adding the dopant to the melt before the ingot is pulled, ion implantation, chemical vapor deposition, and epitaxial growth are some of them.

    Both sides of a PN junction are doped; one side is with a P type dopant such as boron, the other with an N type dopant such as phosphorus. Intrinsic (undoped) silicon does not conduct electricity.
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  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    #4
    Re: doping silicone
    ggunn wrote: »
    One is a crystalline substance from which electrical devices are made, the other is what gives many pole dancers that extra jiggle.

    I'm still not sure I understand. Perhaps if you posted a PICTURE of each (of the above) it would help to show the difference from a visual perspective :)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: doping silicone
    jcheil wrote: »
    I'm still not sure I understand. Perhaps if you posted a PICTURE of each (of the above) it would help to show the difference from a visual perspective :)

    No, it wouldn't. It would just make extra work for moderators.

    The silicon isn't coated. As ggunn says it is infused (or 'modified' if you will) making it a compound rather than a pure element.
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  • ws9876
    ws9876 Solar Expert Posts: 448 ✭✭✭
    #6
    Re: doping silicone

    about the PN jct....some of the web visuals explaining it are better than others. Some make look like there are photons hitting both sides of the PN jct.
    That isnt right
    . Electrons that are bounced off of atoms are forced to go around the PN jct ,thru a load and then rejoin the panel on the other side of the pn jct where the polarity will accept them into holes.Some animations make it look like there are electrons going both ways..
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: doping silicone

    Actually, they do make Bi-Facial solar panels (glass on both sides) solar panels. The P-N Junction itself is not (completely?) direction sensitive regarding light. I believe that the construction of the contacts used to harvest the electricity affects the ability to make cells bi-facial (contacts need to allow light through to underlying Silicon.

    http://www.pv-tech.org/news/spi_2013_panasonic_displays_special_order_double_bifacial_hit_module

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: doping silicone
    BB. wrote: »
    Actually, they do make Bi-Facial solar panels (glass on both sides) solar panels. The P-N Junction itself is not (completely?) direction sensitive regarding light. I believe that the construction of the contacts used to harvest the electricity affects the ability to make cells bi-facial (contacts need to allow light through to underlying Silicon.

    http://www.pv-tech.org/news/spi_2013_panasonic_displays_special_order_double_bifacial_hit_module

    -Bill

    And this is one of the reasons panels aren't very efficient. If they could make that junction truly polarized it would improve things. Maybe someday.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Re: doping silicone
    Cariboocoot wrote: »
    And this is one of the reasons panels aren't very efficient. If they could make that junction truly polarized it would improve things. Maybe someday.
    The pn junction itself is not directionally sensitive, but typically the junction is much closer to one surface of the silicon than the other, so light has farther to travel to reach the junction from one direction than the other. A photon coming into the silicon creates an electron-hole pair, and if that happens in the junction, the built-in field produced by the junction sweeps the electron one way and the hole the other, which produces the current we harvest. If it happens in the bulk (in the silicon but not in the junction) the hole electron pair recombines very quickly and there is no net current.
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