Short answer, no.
Long answer. Unless you have solar panels there is no way to convert the energy, yet if you did have a solar panel, there would be no need for an app as the panel converts the energy for you, but at the rate which it would convert the energy it would be so slow since the panel would be very small to fit on the phone itself, that the benefit would not be enough to be worthwhile. Solar charging a phone with such a small panel would take days from zero to reach a hundred percent charge.