Originally Posted by p008
I think solar charger cannot give enough voltage for phone. I think it just an option to make your phone battery not drain out.
Voltage isn't the issue. You'd just use a boost converter to bump it up to 5V. Every battery pack like the powerbank and similar includes such a circuit, as they either use a 3.7V li-ion (or li-poly, or similar) or a pair of alkalines (1.5Vx2).
The issue is getting enough current to charge something meaningfully.