"Spray on solar panels" usually means making solar cells with a printing-like process. That's been done several times.[1][2] Works fine. But the resulting panels were not cheaper. They're flexible, which makes them popular for boats, tents, and RVs. Lifespan is shorter; you can get a 10 year warranty, but not much beyond that.

[1] http://www.pascaltechnologies.com/files/Whitepapers/Uni-Sola... [2] http://plasticphotovoltaics.org/lc/lc-fabrication/lc-r2r.htm...