  We report on the integration of large area CVD grown single- and bilayer
graphene transparent conductive electrodes (TCEs) on amorphous silicon
multispectral photodetectors. The broadband transmission of graphene results in
440% enhancement of the detectors' spectral response in the ultraviolet (UV)
region at {\lambda} = 320 nm compared to reference devices with conventional
aluminum doped zinc oxide (ZnO:Al) electrodes. The maximum responsivity of the
multispectral photodetectors can be tuned in their wavelength from 320 nm to
510 nm by an external bias voltage, allowing single pixel detection of UV to
visible light. Graphene electrodes further enable fully flexible diodes on
polyimide substrates. Here, an upgrade from single to bilayer graphene boosts
the maximum photoresponsivity from 134 mA $W^{-1}$ to 239 mA $W^{-1}$.
Interference patterns that are present in conventional TCE devices are
suppressed as a result of the atomically thin graphene electrodes. The proposed
detectors may be of interest in fields of UV/VIS spectroscopy or for biomedical
and life science applications, where the extension to the UV range can be
essential.
