I looked into this because it sounded far-fetched.
The power available in sunlight in perfect conditions (at the equator at midday, oriented perfectly, is around 1KW per square meter. Scaled down to iPhone 5 size gives 7.22W. The iPhone charger can provide 5W.
So maybe with extremely efficient photovoltaics you might be onto something, but unless you leave your phone flat in the sun in Ecuador over lunch, this is probably not practical. Mine lives in my pocket.
Wild thinking: this uses infrared. Your body irradiaties infrared. So, Put it on or in your clothing (could be the inside of your t-shirt, or even your underwear), and you're all set :-)
The power available in sunlight in perfect conditions (at the equator at midday, oriented perfectly, is around 1KW per square meter. Scaled down to iPhone 5 size gives 7.22W. The iPhone charger can provide 5W.
So maybe with extremely efficient photovoltaics you might be onto something, but unless you leave your phone flat in the sun in Ecuador over lunch, this is probably not practical. Mine lives in my pocket.