Generation of electricity using renewable energy sources is becoming an integral part of the electrical energy mix. A substantial fraction of the electrical energy is foreseen to be generated by photovoltaic (PV) solar cells that directly convert light into electricity. Large scale application of building integrated PV is envisaged to aid the integration of renewable energy in our society, both from a practical and an aesthetic point of view. For implementation of large-scale PV preferably abundant and non-toxic materials are required as well as production processes for making the solar cells in large quantities [1]. For this purpose silicon is the most preferred element, because of its properties for application in solar cells and because of its abundance, despite the fact that refining and doping of Si are dependant on toxic materials [2]. @en

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