UnwiredView.com noticed that USPTO published Nokia patent application US20120205518:
"Sensing of Photons" by Martti Voutilainen, Markku Rouvala, and Pirjo Pasanen.
The sensor consists of multiple light-sensitive layers of graphene connected to the gates of graphene amplifying FET 106 and 107 and to source of graphene reset transistor 108. Fig. 1 shows a horizontal structure of the pixel, while Fig. 2 shows the vertical cross-section together with RGB color filters 221-223: