Photovoltaic (aka ‘solar’) cells have been around almost since the invention of semi-conductor technology.
At each advance in semi-conductore technology it has been touted that they would become really chaep, and while they have dropped considerably in cost, but have never reached the ‘pennies each’ level.
When Integrated Circuits (‘chips’) came along they grew from pin-head to thumb-nail size, when wafer-scale fabrication arrived they got as big a large coins, as wafer size grew they got to be several inches across.
Then came poly-crystaline, bit larger, somewhat cheaper.
Amophous silicone (basically semi-conductor ‘glass’) they got to be the size of small saucers and quite a bit cheaper.
Now there is organic photovoltaics, currently only about 3% efficient, projected to get to 6% efficient by the time commercial exploitation is reached. (Most ‘solar’ cells are at about the12% level).
The great thing with these is, as it is basically a dye technology they can be printed onto surfaces.
So your mobile phone could still have a design on the back cover, but it would be providing power to top-up the batteries.
It is even reckoned that virtually clear (at visible light frequencies) one could be developed with only slight loss of transmittance, so where you now have a coating in double-glazing to reflect heat back-in and excess sunlight back-out, you would have a photovoltaic one instead.
Being able to basically turn the outside and windows of a house into one giant solar-cell, but could you run a house on DC?