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Office building of Bosch in Wetzlar with a photovoltaic curtain façade
Office building of Bosch in Wetzlar with a photovoltaic curtain façade

New layer systems increase the efficiency of thin-film photovoltaics

Photovoltaics as a relatively young technology is far from being fully developed. Great development potential is attributable to the so-called thin film, because this technology needs a much smaller use of semiconductor material and has more specific advantages. Thus, the semiconductor layers can be applied to the carrier surface cost-effectively on an industrial scale. Thin-film modules can also be architecturally integrated in many ways.

A promising thin-film variant is the CIGS technology, which has been intensively researched in recent years. The window layer (TCO – transparent conductive oxide), which is now in mass production, is based on the ZnO network projects at the beginning of the 2000s. However, the coating process used so far – the “sputtering” of aluminum-doped zinc oxide (ZnO:Al) – reaches its limits. The loss analyzes of components and modules show that this ZnO:Al technology brings about an efficiency limitation and makes it difficult to break down to the modulus effects of the widespread polycrystalline silicon technology.

The research project TCO4CIGS starts at this point. Using optimized TCO layers, the efficiency can be increased noticeably by one to two percentage points at the same or lower production costs, as optical and electrical simulations show. The industry-led consortium has the goal, in a first phase, of identifying the identified potential for innovation. The focus is on model-based shift and process development. The following topics are addressed:

  • Excite the boundaries of the ZnO:Al material system of ceramic targets
  • Alternative doping for ZnO (ZnO:Ga, ZnO:B)
  • Gradient doping in ZnO and seed layer concepts
  • Amorphous TCOs with superior material properties based on a-InO:H,
    A-InZnO and a-ZnSnO

According to benchmark investigations with regard to maximum band gap, transmission, mobility and charge carrier concentration on glass, investigations are carried out on absorber layers. Innovative process technologies are used here. The most promising TCO layer systems of the research group are to be scaled to large module areas in the second half of the project and tested accordingly.