Weiterentwicklung einer Durchlauf – Epitaxieanlage und Implementierung einer turbulenten Gasführung (Volume 1) (English shop)

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To secure the energy supply for the future in the face of increasingly scarce raw materials while simultaneously reducing CO2 emissions, Germany introduced the Renewable Energy Sources Act (Erneuerbare-Energien-Gesetz) in the year 2000. Photovoltaics (PV) plays an important role in this, since its potential is by far the greatest among the renewable energy sources. In order to exploit this potential, substantial investments have been made in basic research and in the development of industrial PV technology. In this way, the costs of PV electricity on German house roofs have been reduced since the year 2000 from approx. 50 ct/kWh to 11 ct/kWh. Essentially two strategies were pursued to achieve this progress. First, the development of amorphous thin-film technologies, which are characterised by an extremely low price but also by a lower efficiency. Second, the development of silicon wafers that are as pure and crystalline as possible, which are indeed expensive but achieve a high efficiency.

In order to combine the advantages of thin-film technology with those of crystalline silicon wafers, the ConCVD (Continuous Chemical Vapor Deposition) is being developed, which represents a link between laboratory equipment and industrial equipment. In order to develop this system further, its safety and reliability first had to be increased. To this end, the drive train, the sensor system, the thermal insulation and the material properties of the internal structure were optimised. Following this classical plant engineering, the quality of the grown layers had to be increased to such an extent that the efficiency can compete with that of standard wafers. For this purpose, a fundamental model was developed that can predict the gas composition at the site of deposition and the resulting crystal quality. In addition to semiconductor characterisation and process optimisation, this decisive work step also required crystallisation theory and flow simulation.

Through the interplay of subject areas from engineering technology and basic research, the performance of the ConCVD could be significantly increased. On the one hand, the layer homogeneity, the deposition rate and the system stability were raised to an industrial level. On the other hand, the crystal quality could be raised to the level of laboratory systems, which led to an increase in solar cell efficiency from 5.1% to 14.1%.