help! any source for multijunction solar cells? (small quantity)

[KTP]

I have been playing around with the low power modes of the MSP430 (0.7 uA running my program at 12khz!) and have found that I can power the little fellow off of a 1 inch by 2 inch amorphous solar cell in a room lit by a single 60 watt bulb.  There is even a bit of power left over, such that I have the MSP430  monitor the voltage of a separate solar charging capacitor, and when it reaches 4V I activate a 2n2222 to dump it into a led for a brief bright flash.  It takes a few minutes for the cap to reach 4V because of the low room light and the fact that the cap is not particularly low leakage type.

Anyway, I would like to make a better solar source for playing around with this, but I want to use a solar cell adapted for all light situations (the amorphous cells work better for indoor scattered light situations, and the mono or polycrystalline cells work better for outdoor sunlight).  The new multijunction cells that work super well in all light conditions (30% to 40% efficient) have been announced for a few years, and are probably used in most space applications, but I cannot find a source for one or two of these.  I don't really care if they are $100 or even $500 a watt, since I only want a very tiny cell, of maybe 50mW maximum.  Any suggestions?  I would like to keep everything as small as possible too.

[davidf2281]

Hi KTP,

Did you ever get a solution to this? I'm in a similar boat at the moment, powering a uController so I only need a tiny dribble of current (about 50uA average), but enough voltage in ambient light to get 3V+, so I'm thinking probably a cell with nominal 9-12V but very low current rating. Can't find anything in the size range I need (couple of inches by couple of inches), even when browsing alibaba etc.

If you've managed to find anything I'd love to hear about it (or from anyone else with a magic source of very small, 9-12V panels...).

David.

[LukeW]

You can get the Boeing/Spectrolab/Sensormetrix "TASC"s (Triangular Advanced Solar Cells), which are small triangular offcuts from the multijunction space-rated PV wafers they're making for space/military big-budget customers, and they're sold relatively cheaply to users working in education and building CubeSats and what not.

http://www.spectrolab.com/faqs-space.htm