Thin-film poly-crystalline silicon (poly c-Si) on glass obtained by crystallization of an amorphous silicon (a-Si) film is a promising material for low cost, high efficiency solar cells. Our approach to obtain this material is to crystallize a-Si films on glass by solid phase crystallization (SPC). As the grain size of SPC poly c-Si films will be smaller than that of multi-crystalline wafers, lower solar cell efficiencies are expected for this technology. Despite the smaller grain size, a 2-micron-thick polycrystalline silicon solar cell with light trapping was shown to have a conversion efficiency of more than 10% [1]. Obtainable efficiencies up to 15% are expected for solar cells made using SPC of a-Si:H films. Expanding thermal plasma chemical vapor deposition (ETP-CVD) was used to prepare hydrogenated a-Si films; this technique is chosen because the deposition rates are much higher than with plasma enhanced CVD. A-Si:H films with different hydrogen contents were annealed using temperatures ranging from 500 °C to 700 °C. The evaluation of the films after annealing treatments revealed that the hydrogen content and bonding configuration did not influence the structural properties of the crystallized films significantly. The average crystallite size in the fully crystallized films was between 100 and 150 nm. Full crystallization of 1 micrometer thick films was achieved within 20 minutes for annealing at 625 °C and 650 °C. During annealing at 600 °C crystallization is much slower, and no crystallization is observed at 500 °C. The relation between the annealing temperature and the rate with which the films are fully crystallized is of great importance to develop a solar cell technology, to limit the thermal budget and processing time.@en

A systematic and detailed analysis of the influence of hydrogen (H2) dilution of silane (SiH4) on the structural properties of thin hydrogenated silicon (Si:H) films was carried out. The Si:H films were prepared by plasma enhanced chemical vapour deposition method at different H2 to SiH4 flow ratios (R) ranging from R¿=¿0 to 40. A detailed structural analysis was carried out by X-ray diffraction (XRD). In order to suppress the XRD intensity from the substrate, Si:H films were deposited onto a [100]-oriented single-crystalline silicon substrate and XRD was carried out with a thin-film attachment. The XRD analysis demonstrated that the first diffraction peak in the Si:H films corresponded to the signal from silicon hydride (Si4H) ordered domains having tetragonal lattice structure. The full width of half maximum (FWHM) of the peak was decreasing with increasing H2 dilution, and remained nearly constant for R¿¿¿20. The FWHM values confirmed that the Si:H films grown at R¿¿¿20 are more ordered than films deposited at lower R. This trend was confirmed by the Raman spectroscopy from the analysis of the shift of the Raman amorphous peak.@en