is there any method of cutting mono cells?

Skyko

I am having a hard time locating a source of small monocrystalline cells (I gave up on trying to get the triple junction space satellite cells...you just about have to be NASA to get your hands on them). I was sampled a very very cool panel by Sharp, which is about 3/4 the size of a business card, about twice as thick, and is 3.6 grams. It has a Voc of just over 6 volts and will produce 0.4 watts in full sun (maybe a bit more than this, as I was getting 4.6 volts at 75mA in hazy Seattle conditions yesterday). Interestingly, it also produced far more power from indoor artificial lighting than the amorphous panel of similar size and a polycrystalline panel of double the size. Under a single 60 watt bulb at a distance of 8 feet I was getting 2.9 volts into a 10K load, which is 290uW. This is actually enough to harvest over time to power the rf transmitter and microcontroller in my design (the microcontroller only consumes 2uW in sleep with the watchdog running, and less than 50uW while running off a 32khz watch crystal. I was told these were monocrystalline panels, but they really look like no other type of panel I have seen before.

The problem is these are prototype panels out of Japan (even the data sheet was only in Japanese) and will not be in production until next year, at which time I would need to order a minimum of 800 at what knows price.

So...I am trying to find information on the web or from someone about cutting up monocrystalline cells to make a similar panel. There are several types of 6x6 cells on ebay for $1 a watt or less, but I am not sure of a process that can neatly cut them into little 1" x 1/2" rectangles, or even if the bus bars would still connect enough to maintain the efficiency when cut like this.

Any suggestions? I doubt the Sharp guys will send me 40 more samples (that is about how many units I need to produce).

RCinFLA

Re: is there any method of cutting mono cells?

Monocrystaline cells are cut with a di-ionized water cooled diamond saw but that is on wafers that have been processed knowing the cut position in advance.

Cutting through the metalization will likely damage the cell and make it vunerable to future corrosion.

AntronX

Re: is there any method of cutting mono cells?

RCinFLA wrote: »

...Cutting through the metalization will likely damage the cell and make it vunerable to future corrosion.

Are you sure? How about snapping the cell while it being held between flat metal sheets to control the location of snap. I was just thinking about cutting many small 2x1 inch cells from one 6x6 cell to make a solar panel that follows curvature of car's roof. The corrosion would not be an issue after the cell is encapsulated in resin.

BB.

Re: is there any method of cutting mono cells?

Exposing the edge of the copper/tin(?) at the cut line may expose you to tin whiskers and metal migration (don't know--but could be a problem). We had those problems with printed circuit boards...

-Bill

AntronX

Re: is there any method of cutting mono cells?

Wouldn't tin whiskers simply burn off due to currents involved? 1x2 inch cell would have 0.44 Amps. Do tin whiskers grow trough solid epoxy resin?

BB.

Re: is there any method of cutting mono cells?

Whiskers and Dendrites grew very nicely in our Printed Circuit boards (Between layers of FR4 epoxy and fiberglass). Believe me, you don't want to burn those off--carbon trail, lots of nice new chemicals (products of heat and possible combustion) to do wild and wonderful things to the metal that is left.

-Bill

PS: I am not saying I know this to be a problem with fab and cut solar cells--It is just a concern I have that would need to be investigated if this was intended to be a high reliability project.