In this paper a set of one-dimensional simulations of a-Si:H p-i-n junctions under different illumination conditions and with different intrinsic layer are presented. The simulation program ASCA permits the analysis of the internal electrical behaviour of the cell allowing a comparison among the different internal configurations determined by a change in the input set. Results about the internal electric configuration will be presented and discussed outlining their influence on the current tension characteristic curve. Considerations about the drift-diffusion and the generation-recombination balance distributions, outlined by the simulation. can be used to explain the correlation between the basic device output. the i-layer characteristics (thickness and DOS). the incident radiation intensity and photon energy. (C) 2002 Elsevier Science B.V. All rights reserved.