The spectral response and the photocurrent delivered by entirely microcrystalline p-i-n-Si:H detectors are analyzed under different applied bias and light illumination conditions. The devices consist of a ZnO covered glass substrate, followed by a p(+)/i/n(+) structure, and an Al top contact. The light is incident either through the glass or through the rear part of the device. The spectral range depends on the illumination side. Under rear illumination the spectral response is extended beyond 1000 nm and has a maximum near 700 nm with a good rejection of the blue spectrum. If the light is incident through the glass the same infrared response is observed, however, in the visible range the maximum is shifted to the blue region. Numerical modeling of the VIS/NIR detector, choosing appropriate band discontinuities near the grain boundaries and interfaces complements the study and gives insight into the internal physical processes. We suggest that transport will proceed on parallel paths along the amorphous, the crystalline, or both phases depending on the wavelength. The enhanced sensitivity to the red/infrared region is then related with the operation of the crystalline-like diode while the spectral responsivity in the 'blue' region is ascribed mainly to the amorphous-like photodiode.