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Making solar cells more efficient and cheaper layer by layer

The efficiency of solar cells can be increased with the so-called PERC technology (Passivated Emitter Rear Cell). The current yield increases because the back of the solar cell is passivated. However, additional process steps with high passivating and at the same time cost-effective layer systems are required for the production process. Special passivation layers such as aluminum oxide (Al2O3) or silicon nitride (SiNx), which are deposited on the cell by means of plasma technologies, play an important role here.

A goal of the SIMPLEX research project is the comparison of Al2O3 deposition by means of different plasma-enhanced gas-phase deposition (PECVD) methods with regard to layer quality and cost structure. Experiments are performed and compared in different process modules. Compared to the current state of the art, the processes are to be optimized and the use of the material reduced. In addition, further Al-based layers are being investigated and developed for their suitability in crystalline silicon solar cells.

To achieve these objectives, in-situ characterization methods are used and further developed in SIMPLEX. This relates on the one hand to electrical and spectroscopic measurement methods for characterizing the plasma reactors used in the coating process and, on the other hand, to optical and chemical methods for analyzing the layers produced. The ex-situ characterization methods used as a supplement should allow an additional analysis of the process results. The work is carried out partially on already existing plasma reactors and for additional measurements of the plasma parameters and investigations of the layer formation process on new model reactors. The experimental work is supported by modeling of the plasma process, gas supply and disposal and the conversion of the gases in the plasma and on the walls into layer forming molecular fragments.

The developed coating processes are applied to crystalline silicon solar cells, which are partly integrated into solar modules. In particular, the long-term stability of the solar cell performance is investigated.


Circular inductively coupled plasma (ICP)
Calculated electron energy distribution for circular ICP plasma
Induced electric field strength calculated from ICP coil current