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photovoltaic cell spectral sensitivity?

Discussion in 'Electronic Design' started by Mark Fergerson, Oct 18, 2004.

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  1. I'm wondering what part of the spectrum most solar cells
    (frinst those I salvage from cheapos calculators) are best
    able to convert to current.

    So I Google myself silly to little avail; most cells on
    hand appear to be the single-crystal type, and near as I can
    tell they digest near-IR best which is discouraging. I'm
    assuming their visible appearance (many different colors) is
    due to antireflection coatings rather than indicative of
    their particular absorptive properties.

    Anybody got a better set of Google terms that what I
    thought were obvious, or maybe a decent website preferably
    with some damn numbers?


    Mark L. Fergerson
  2. I don't, right off the bat. But I would anticipate that the sensitivity would
    be poorly controlled (in other words, some batches will behave differently than
    other batches) in order to keep the whole process as cheap as reasonable and
    that the overall response would be otherwise similar to the usual Si based lower
    cost detectors you might find in a Hamamatsu catalog. Roughly speaking.

    But I'll be interested to hear what you discover here.

  3. See, you found the data already.
    You would be best off adjusting your needs and expectations,
    you most likely aren't going to be able to change the properties
    of Si.
    They have no antireflection coatings. Most are coated for humidity
    protection. The color is part of the processing. The most efficient
    cells are bright blue: that sort of says what color light they absorb,
    ne'est ce pas?
  4. rob

    rob Guest

    try the group
  5. Well, poop.
    That's not really the problem. In the fine tradition of
    this group, I stated part of my needs without saying what
    I'm trying to do. See, I plan to hide said scavenged cells
    under simulated gemstones (don't ask why), and now I get to
    find suitable fake stones that will pass enough NIR to be
    I've seen info that claims they are indeed AR coated, but
    I see your point.


    Mark L. Fergerson
  6. Some minerals should pass IR very well. I know quartz does,
    that should open up a whole range of colored quartzs. I have
    a suspicion that garnet is also IR transparent. And diamond
    certainly is.
    I'll be darned. It's a coating of TiO2 --

    I had always thought of titanium oxide as the
    'white pigment' in paints, etc.
  7. Rich Grise

    Rich Grise Guest

    Oh, he didn't say anything about doing any discovery - he just posted to
    the group to get the answer without doing any of his own homework, like we
    all do! ;-)

    But I'm really, really intrigued by the app here.

    Is quartz really IR transparent? I know it's one of very few items
    transparent to UV.

    How hard would it be to make some fake gems out of acrylic? Do they have
    to have realistic heft? And, is acrylic IR transparent? What plastic do
    they use for the windows on remotes?

  8. Clarence

    Clarence Guest

    There are lenses made of Germanium! They look gray in visible light, but work
    as lenses for IR.
  9. A couple of things to keep in mind. Glass, the common form, is a combination of
    quartz, soda (lowers melting point) and lime. Earlier, soda was hydrated sodium
    carbonate with and lime and magnesia as mixed impurities. Today, it's sodium
    oxide. Lime (quicklime) is calcium oxide and adding it keeps the resulting
    glass from being water soluble, a problem that adding the soda creates. Fused
    quartz (or silica) is a non-crystalline glass without the soda and lime stuff
    added in. It's nice, pure SiO2, except it's the non-crystalline glass form.
    (Ceria or titania (oxides) are also added to glasses and this reduces the short
    wavelength side of the passband.)

    Glass starts blocking around 380-400nm, I think, and (from actual measurements I
    made some years ago) is pretty much opaque by the time you get to 310nm. But
    there are differences in this, even in the garden variety 'green', 'brown' and
    'clear' glasses used for various bottling needs. Much of the clear stuff, if
    memory serves, passes some even at 320-330nm.

    Even the better fused quartz (no impurities) has dropped to some 70%
    transmission by 200nm and I don't think it goes much past 150nm. Often,
    titanium dioxide is added to cut sharply anything shorter than 220nm or so. And
    I think it starts dropping down on the long side at about 3.5 micron and is
    quite dead before 5 microns.

    Since UV contains wavelengths shorter than 100nm, I don't consider quartz to
    really be a good, overall UV window -- unless all you like is the longer
    wavelengths of it. For more UV transparency, sapphire works much, much better
    and is available as windows, lightpipes, etc. (Diamond is just plain stunning
    -- but then, diamond always seems to have a one-upsmanship going for it [best
    heat conduction, best transparency bandpass, hardest, etc.])

    Sapphire also has a much wider acceptance angle for lightpipes, about twice that
    of quartz. That can be good or bad, depending on need, but it's almost
    worthless if you couple the sapphire lightpipe with an optical fiber, since the
    fiber is quartz and immediately strips the wide NA off and you lose the view
    unless you use some kind of diffuser between them.

    Keep in mind, this is all from memory so I could be wrong on several
    particulars. But it's what my poor memory tells me.

  10. Fabulous stuff.
    This TiO2 can also be baked into glass to make it conductive.

  11. Ken Smith

    Ken Smith Guest

    Yes, acrylic is IR transparent (mostly)
    They make lenses for IR work out of the stuff.
  12. Ken Smith

    Ken Smith Guest

    In this case the white is because it total-internal reflects the light
    back. A solid chunk would let the light through.
  13. Now Rich, that's unfair. I said I Googled myself silly.
    Apparently I simply lacked some appropriate search terms.
    Heft would be nice as would durability, and yes, quartz
    is good deep into the IR. I'm leaning toward clear quartz (I
    have plenty of old-fashioned radio crystals on hand)
    roughened on the back side to act as a diffuser.

    Mark L. Fergerson
  14. boB

    boB Guest

    Yes, germanium. We (at work) had a $50,000 IR camera for a week and
    the salesman told us the lens was made of gerrmanium. expensive
    lenses too....

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