Here is an interesting article (in french, sorry), about a phone made with the sunpartner technology.
http://www.frandroid.com/smartphone/...aique#comments
google translate, in english:
https://translate.google.fr/translat...photovoltaique
Among other things, it speaks of a 10% loos of luminosity. (Don't apply as is to e-ink screen, because of frontlight.)