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The hydrogen plasma passivation of thin film polycrystalline silicon (pc-Si) was investigated in conjunction with plasma texturing process to make efficient heterojunction solar cells. The pc-Si layers were first treated using direct and remote hydrogen plasma technologies. The heterojunction solar cells were then fabricated by subsequent deposition of i/n+ a-Si:H. Hydrogenation at high temperature (610 °C) results in enhanced dissolution and diffusion of hydrogen in pc-Si by a factor of about 3 and 4, respectively, in comparison with those at low temperature (420 °C). The hydrogen atoms in the pc-Si layer mainly bond to the silicon dangling bonds and form complexes with dopant atoms. In addition, platelets defects are generated by the hydrogen plasma in the sub-surface region of pc-Si hydrogenated at 420 °C and cause higher saturation current in the space charge region whilst they form in the region deeper than 1 μm at 610 °C. Removal of the platelets using SF6/N2O plasma post-texturing after low-temperature hydrogenation not only enhances the short circuit current but also improves the open circuit voltage and the fill factor simultaneously. Combining plasma pre-texturing with high-temperature hydrogenation, the best 2 µm-thick pc-Si heterojunction solar cell reaches an efficiency of 8.54%.

Thin-film polycrystalline silicon (pc-Si) solar cell technology tries to combine the cost benefit of thin-film technology and the quality potential of crystalline Si technology. For this type of solar cells the challenge is to fabricate high quality coarse-grained (grain size of 1–100 µm) layers on non-silicon substrates in combination with superb light management. One possible material fabrication approach is metal induced crystallization (MIC). Many metals lower the crystallization temperature of a-Si but for photovoltaic (PV) solar cell applications aluminum seems to be the most interesting. Approximately a decade after the suggestion of Nast et al. to use aluminum induced layer exchange for thin-film solar cells, this paper will discuss the aluminum induced crystallization process itself as well as the implementation into workable solar cells. The record aluminum induced crystallization (AIC) solar cell today features an energy conversion efficiency of 8.5%, too low to be competitive with other PV technologies. The main problems and limitations as encountered today will be described. We believe that an energy conversion efficiency of 8.5% is not the limit of AIC solar cells. Different possible solutions to improve the AIC process as well as the resulting solar cells will be discussed together with our vision on the direction and future of AIC solar cell research.

Crystalline Si (c-Si) technology is dominating the photovoltaics market. These modules are nonetheless still relatively expensive, in particular because of the costly silicon wafers, which require large thickness mostly to ease handling. Thin-film technologies, on the other hand, use much less active material, exhibit a much lower production cost per unit area, but achieve an efficiency still limited on module level, which increases the total system costs. A meet-in-the-middle is possible and is the object of this paper. The development of c-Si thin-foil modules is presented: first, the fabrication of the active material on a glass module and then the processing of the Si foils into solar cells, directly on module level. The activity of IMEC in this area is put into perspective with regard to worldwide research results. It appears that great opportunities are offered to this cell concept, although some challenges still need to be tackled before cost-effective and reliable industrial production can be launched. Copyright © 2012 John Wiley & Sons, Ltd.

We investigate the effects of grain size inhomogeneity on the performance of thin film polycrystalline silicon solar cells with columnar grains. We focus on cells with an exponential distribution of the grain diameter, which approximates the grain size inhomogeneity in polycrystalline silicon films made via aluminum induced crystallization (AIC) with low temperature annealing. Through equivalent circuit simulation, we demonstrate that the size inhomogeneity will only play a role when intra grain defects, which is common in AIC cells, can be avoided. We further demonstrate that the inhomogeneity itself is not a dominant factor which limits the efficiency of these cells.

Polycrystalline silicon (grain size ~ 0.1–100 μm) solar cells on foreign substrates are a promising approach for the next generation silicon solar cells. Aluminum-induced crystallization AIC in combination with epitaxy is a possible way to obtain such absorber layers. It is believed that Si islands present on the surface of AIC seed layers have a negative effect on the epitaxy. The removal of these islands could therefore lead to an increased absorber layer quality and solar cell performance. In this paper, we present a selective island removal procedure based on the Al layer already present after AIC annealing. By selecting an etchant which removes Si at least as fast as Al (in this paper plasma etching using SF 6 ), the Al layer acts as a perfectly aligned etching mask for the fully developed islands.

Polycrystalline silicon (pc-Si) thin-films with a grain size in the range of 0.1–100 μm grown on top of inexpensive substrates are economical materials for semiconductor devices such as transistors and solar cells and attract much attention nowadays. For pc-Si, grain size enlargement is thought to be an important parameter to improve material quality and therefore device performance. Aluminum-induced crystallization (AIC) of amorphous Si in combination with epitaxial growth allows achieving large-grained pc-Si layers on nonsilicon substrates. In this work, we made pc-Si layers with variable grain sizes by changing the crystallization temperature of the AIC process in order to see if larger grains indeed result in better solar cells. Solar cells based on these layers show a performance independent of the grain size. Defect etching and electron beam induced current (EBIC) measurements showed the presence of a high density of electrically active intragrain defects. We therefore consider them as the reason fo...