A series of nip-type microcrystalline silicon (μc-Si:H) single-junction solar cells has been studied by electrical characterisation, by transmission electron microscopy (TEM) and by Raman spectroscopy using 514 and 633 nm excitation light and both top- and bottom-illumination. Thereby, a Raman crystallinity factor indicative of crystalline volume fraction is introduced and applied to the interface regions, i.e. to the mixed amorphous-microcrystalline layers at the top and at the bottom of entire cells. Results are compared with TEM observations for one of the solar cells. Similar Raman and electrical investigations have been conducted also on pin-type μc-Si:H single-junction solar cells. Experimental data show that for all nip and pin μc-Si:H solar cells, the open-circuit voltage linearly decreases as the average of the Raman crystallinity factors for top and bottom interface regions increases. © 2003 Elsevier B.V. All rights reserved.