Glass/ZnO:Al/p (SixC1−x:H)/i (Si:H)/n (SixC1−x:H)/Al (0<x<1) heterojunction cells were produced by PE-CVD at low temperature. Junction properties, carrier transport and photogeneration are investigated from illuminated current- and capacitance- voltage characteristics and spectral response measurements, in dark and under different illumination conditions. For the heterojunction cells high series resistance around 106 ω and atypical J-V characteristics are observed leading to poor fill factors, also it was observed that the responsivity decreases with the increase of the light bias intensity. For the homojunction the behaviour is typical of a non optimised p-i-n cell and the responsivity varies only slightly with the light bias conditions. A numerical simulation gives insight into the transport mechanism suggesting that in the heterojunctions and in dark conditions the transport mechanism depends almost exclusively on field-aided drift while under illumination it is dependent mainly on the diffusion of free carriers.