There are plenty of solar-powered device chargers out there, but you can save a few bucks (and have some fun) by hacking together your own.
Instructables user ASCAS built a multi-device charger for small change, though the solar panel used seems to be hard to find. If you can locate a similar model though, the rest of the project is pretty easy.
In essence, you’re just hooking up the solar panel to a USB power bank, and mounting that to the back of the panel. If your solar panel runs at over 5V, you’ll want to hook up a regulator to avoid damaging the external battery over time. The source link will show you how to do that.
DIY Portable USB Solar Charger ($20 – 4 Ports) [Instructables]