Many people who hear about solar chargers say that it's dangerous for your cell phone to be exposed to sunbeams. They're totally right, but they miss a very important point. While using a cell phone solar charger you don't have to keep your device near the charger. You can just put the charger in a place where there is a lot of solar energy and wait until it charges itself and then take it to shade where you keep your cell phone and then transfer the electricity from the charger to your device.
The cost of such charger is relatively high, it's much more expensive than an ordinary charger, but on the other hand the technology used in it is much more sophisticated and all solar oriented equipment is expensive. A basic one will cost you around $20.