As James points out, solar panels on phones is useless.
I have a
solar battery charger / LiPo combo designed to recharge a phone. The LiPo battery is 2Ah and can deliver 1 full charge to a phone. Positioning the solar panel in the best direction I can, it takes an entire sunny day to charge the battery. The panel has a surface area about 4x that of a typical phone.
Yesterday I left my phone outside in the sun while I dug for a broken water main. 30min later I went to my phone to check the time, and it had shut off due to the temperature being too high.
Leaving phones in the sun is not good for them.
Phones don't need quad core processors. If people didn't expect their phones to be as speedy as their PCs, the battery could last much longer.