A study of the i-layer porosity as a function of the deposition parameters by PECVD technique, is presented here. It is demonstrated in particular, that for a fixed deposition rate of 2 Å/s, increasing the plasma power tends to increase the layer density, while increasing the pressure tends to increase the layer porosity. Regarding the cells, no correlation between the layer density and the initial cell performances is observed. On the contrary, the i-layer porosity seems to influence the cell degradation: High porosity of the i-layer leads to high degradation, which gives an easy tool to investigate the layer quality. © 2003 Elsevier B.V. All rights reserved.