Some notes on Panasonic Amorton solar cells

These are just rough notes that might help someone else in their personal electronic projects.  About Amorton’s indoor solar cell products, AM1456, AM1417, etc.

These solar cells are like what you see in calculators.  They are only a few square centimeters or larger.  Typically like pieces of glass.

For low light

These indoor products are for low light.  They are characterized for as little as 50 lux, which is not much light, typical of an indoor space with average lighting.  A room with a sun facing window, on a clear or overcast day, typically has much more light.  Even typical artificial lighting provides this much light.

The power available at these lighting levels is only a few uA.  Also, the Vope (which is the operating voltage, which really means the maximum power voltage, see MPPT) is a fraction of the Voc (voltage open circuit)  in much stronger light.  For example, if the panel has four cells which each deliver a maximum of 0.6 volts, the Voc might be 2.4V but the Vope in 50 lux might be only 1.4V.

You should design your circuits to operate around Vope, since if you design to operate at the Voc, it will take strong light, and the power delivered will be smaller than you could get at Vope.

(PowerFilm does not characterize their film solar cells at such low light levels.  But they recently started selling LL3-37, which IS targeted for low light.)

Availability

Some of the glass ones are available from Digikey and Mouser.  The film versions don’t seem to be readily available in small quantities to retail buyers.

Solderability

The models that are commonly available have pre-soldered wires, AWG 30.  I have had good success in unsoldering the wires, leaving the solder ball, and soldering on a different wire (including tinned piano wire.)

Surface Mount

I also tried unsoldering the wire, cleaning the pad with flux and desoldering braid, and trying to reflow surface mount.  With very poor results (say one success in three.)  The manufacturer said this is not a supported use.  After the failure, you see a brown surface that solder won’t stick too.  Evidently the ‘interface’ between the solder and the semiconductor is very thin and its solder ability easily destroyed.

Some of the product variations for AM1456, AM1417 have no pre-soldered wire, but only conductive paste, and they are available only in large quantities (AFAIK.)  I don’t think these are intended for reflow soldering either.

Amorton recently started selling model AM1606, which IS intended for surface mount (SMD.)  Available from Mouser.

Durability

They seem relatively robust.  I have dropped them from desktop height onto concrete and they don’t seem to break.  I have had a few, small, conchoidal chips out of the edge, seeming cosmetic, not affecting the power out.

Under extreme mechanical stress, the soldered pads occasionally detach at the ‘interface’.  See above re surface mount.

Safety

The glass edges are not sharp.  I have never cut myself on the edges.  I suppose the manufacturing process somehow rounds the edges a little, even though they appear quite square.  However, I suppose the edges are intended to be enclosed in a frame.

But since they are small and glass, they ARE a hazard for small children, and if they should break into pieces.

 

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Cutting Powerfilm thin-film solar cells

Experimental result: you can cut Powerfilm thin-film solar cells.  I wrote this blog because whenever I search for that topic, the usual results are obscure references to “follow the instructions” and the manufacturer’s website doesn’t seem to discuss it.   Maybe this is not an important use case.  But I wanted a solar cell (a panel really) smaller than the smallest one made by Powerfilm (model SP3-37, which is about 4×6 cm.

Cutting down a thin-film solar cell

Simply take a sharp scissors and cut in on a line along the direction of the fingers (the T-shapes that seem to gather charge from the top of one row of cells and carry it in series to the bottom of the next row of cells.)  In other words, each piece retains a portion of the silvery contact bars at opposite sides of the panel.

I was able to cut on SP3-37 into thirds very nicely (each piece about 1.2 cm by 6 cm.)  For some reason, there is a slight voltage drop on the pieces.  Under a certain light condition, the whole panel generated 3V open circuit, a two-thirds piece generated about 2.8V and a one-third piece generated about 2.6V.

Cutting in in thirds avoids cutting into the fingers, and gives three pieces that look about the same (with the finger down the middle.)  I don’t see why you couldn’t cut along the fingers and get six pieces.  I would guess that if you cut so that some piece has no fingers, that piece would have much reduced function.  But I haven’t tried it.

Cutting in this way leaves the pieces with edges that are not sealed by the outer covering plastic laminate of the entire panel.  I can’t say what the effect is on the lifetime, or warranty.

When I first contemplated cutting a thin-film solar cell, I worried that the shearing action would somehow short the layers of the solar cells.  Evidently not, at least in the short term.

Trimming the silvery contact bars

In my opinion, the silvery contact bars are much larger than they need to be.  Probably the manufacturer contemplates they need to be that large for ease and reliability of soldering to them, and that they will always be hidden by a bezel of the enclosing product.

Some applications, such as in RC planes, for which the manufacturer makes a lightweight model, you would also want to trim off excess silvery contact bars.

I haven’t yet tried to trim the silvery contact bars.

Simple trimming of excess

On the stock part, you can see where the outer plastic laminate seals the edges, away from any functional layers.  In other words, you can see the channels where the manufacturer has cut a strip of the parts into parts.  The stock part seems to have some excess, especially along the edge having a silvery contact bar.  Even if I don’t want a smaller panel, I usually trim this excess away just for neatness and to save weight.

Cutting non-rectangular shapes

Suppose you wanted to cut a thin-film solar panel into a decorative shape.  I suppose you could do that as long as you retained a portion of each silvery contact bar.

Cutting down the number of cells in series

I don’t think you can do that.  You are stuck with the lowest voltage panel that the manufacturer makes (3V: 5 cells of 0.6V each, in series.)  In my opinion, there will be demand for 1.5V panels.  Many electronics nowdays work at only 1.5V.

But it might be possible to cut the thin-film solar cell orthogonally to the fingers, and fabricate a new silvery contact bar to replace the one you cut away.