Check this out, this is the best of both worlds (but the price tag reflects it): http://www.goalzero.com/
I saw this setup in person at a festival up in Richmond. It's a solar panel that connects into a set of rechargeable batteries. Basically, you can charge the batteries off the panel OR off of a computer/the wall, and then take it with you out on the trail. When you need the juice, plug the batter pack into your phone and presto! If you wanted (or if your rechargeables ran out), you could also load regular batteries into the charger pack for more energy.
They sell several different versions of their product, including a massive solar panel array and a large battery pack big enough to power laptops or small appliances.