Solar cells have always seemed a little magical to me. I don't really understand how they are made except for that is is a big industrial process. I have asked people who seem to know and been told there is no way to build one yourself(the cell not just the housing). However I just happened to find this video that shows you how to build one using using donut powder (little scary to think huh?) and tea:
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Also see: http://www.wired.co.uk/magazine/archive/2010/03/how-to/how-to-make-your-own-solar-cell and http://www.solideas.com/solrcell/english.html
Now we are not talking about lots of electricity or high efficiency but it still seems like a very cool project. Only issue is they just pass over this whole conductive glass thing like you can pick it up at the corner store. Luckily there is another video on how to make conductive glass using toothpaste (maybe it counteracts the donut powder?).
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Seems like it would be a fun project to build one, just to see how much power we get from it.