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The next generation of stacked solar cells is here

Thin-film silicon solar modules are a relatively inexpensive alternative to conventional solar cells made of crystalline silicon. EU-funded researchers have increased the efficiency of these next-generation solar cells and brought them one step closer to the market.

Industrial Technologies

In thin-film solar modules, the silicon is applied to a substrate as a layer about 3 μm thick, which does not need to be cut out from expensive wafers with high precision. These thin-film silicon solar modules made of two layers one on top of the other that absorb different fractions of light are particularly efficient. However, high efficiencies are gained at the cost of increased complexity. Each layer is divided into several sublayers that influence each other in a complex manner. Because these interactions are difficult to predict, industrial thin-film silicon solar cells are based on proven combinations of components and substrates. In the EU-funded project FAST TRACK (Accelerated development and prototyping of nano-technology-based high-efficiency thin-film silicon solar modules), scientists pooled their expertise to combine the best possible components. By harmonising different approaches for light management and optimising light absorber materials, a new generation of thin-film silicon solar modules was designed with an efficiency of 12 %. The corresponding costs should be below EUR 0.5 per watt nominal power. To achieve this high efficiency, the scientists experimented with various nanomaterials and optical functional layers, but also redefined the entire process chain. They focused on improving the fill factor and open-circuit voltage to boost the final energy conversion efficiency of the thin-film silicon solar modules. Both the optical and electronic properties of the various layers were effectively influenced by making use of new nanomaterials such as nanocrystalline silicon oxide. The solid structure of this multiphase material displays greater degrees of freedom than pure silicon. The surface conditions of the upper and lower layers were also scrutinised. Structures on a nanometre scale helped to improve light trapping. The texturisation was accomplished by nano-imprinting on glass and new equipment for wet-chemical etching of transparent conductive zinc oxide layers. As a result of the close cooperation between research and industry partners, the FAST TRACK project has resulted in improving the energy conversion efficiency while reducing the production costs. These advancements in the front line of thin-film silicon technology have already been implemented in production.

Keywords

Solar cells, thin-film silicon solar modules, crystalline silicon, nano-imprinting

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