Hydrogenated microcrystalline silicon i-layers were deposited with a fixed silane concentration on various substrates and incorporated into n-i-p solar cells. 'Average crystallinity' and detailed microstructure of layers and devices were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The role of the substrate is thereby shown to be very critical; a change in the substrate can cause a transition from amorphous to microcrystalline growth in micrometer-thick layers. When crystalline growth occurs, the layer microstructure is depth-dependent. © 2002 Elsevier Science B.V. All rights reserved.