A technique comprising: forming on a support film a first stack of layers defining an array of photodiodes; forming over the first stack of layers in situ on the support film a second stack of layers defining electrical circuitry by which the photoresponse of each photodiode is independently detectable via an array of conductors outside the array of photodiodes; wherein forming the first stack of layers comprises depositing an organic semiconductor material over a first electrode, and depositing a second electrode over the organic semiconductor material, wherein the electrical circuitry comprises transistors including photosensitive semiconductor channels, and the second electrode also functions to substantially block the incidence of light on the photosensitive semiconductor channels from the direction of the support film.