Effusions Measurements

© Fraunhofer CSP
Effussion measuring station in the device development laboratory of the Fraunhofer CSP.
© Fraunofer CSP
Hydrogen effusion as a function of temperature, measured for SiN:H layers of different composition.

A unique measurement system for measuring the quality and properties of diffusion barriers in silicon solar cells is now available at the Fraunhofer Center for Silicon Photovoltaics CSP. This system enables the determination of the silicon solar cell coating properties.

In an industrial production of solar cells, the passivation of the silicon volume  by hydrogen is of elementary importance in order to achieve a maximum cell efficiency. During this passivation, a hydrogen-rich silicon nitride layer (SiN:H layer) is deposited to a solar cell surface in a plasma process. Subsequently, the SiN:H layer is activated in a thermal process, whereby the hydrogen from this layer can penetrate into the silicon volume. There, the hydrogen binds so-called recombination centers and thus compensates for impurities, for example. This process improves the solar cells efficiency.

However, during thermal activation of the SiN:H layer also the evaporation of hydrogen into the atmosphere (effusion) is possible. Hydrogen atoms can be lost. Thus, knowledge of hydrogen effusion may help to optimize SiN:H passivation. The effusion measuring station developed at the Fraunhofer CSP makes it possible to determine the hydrogen concentration in the SiN:H layers. The effusion and diffusion measurement of hydrogen supports the development of an optimized SiN:H volume passivation, for example by the analysis of so-called diffusion barriers.