Okay I see. Well when you do buy one, I would recommend one that is more like a box, where you phone plugs into it via the USB cable, opposed to one that is a case, with the solar panels on the back of it, requiring you to leave your phone in the sun, where the battery is baking.
At least this way, you can keep the charging box in the sun light, and your phone out of the sun light, instead of letting your phone sit in the sun with a case on it that draws heat directly to the device, if ya know what I mean.
I mean, do what you would like, that's just how I would go a out getting a solar powered charger.