I suspect this will happen in another 5-6 years when we have PV coatings that don’t add weight or size to the phone. Right now the weight and size would make this unappealing to mass market.
soon we’ll reach the point where the back of all consumers devices, phones, ipods etc can be a very thin PV layer that adds almost zero weight and you can just place the device upsidedown in the sun to gain some charge… as well as having standard charging methods.