Texturing and Passivation

© Fraunhofer CSP

REM image of a moth-eye pattern for crystalline silicon solar cells in plan view.

Future high-quality solar-cell technologies and solar plants will have to fulfil high demands. Apart from low costs, the quality and a long service life of the products will have an essential role to play. To this end, the Coating and Passivation team works on two important applications:

  • Development of a process for plasma texturing the surface of silicon wafers with little surface damages and high light absorption: This plasma texturing should become seamlessly integrated into the current production processes and in the midterm replace Wet Bench 1.
  • Development of a charge-carrier-induced passivation of efficiency-limiting defects in mono-crystalline and multi-crystalline silicon: The intention is to avoid the light-induced degradation of the solar cells.

In addition, the Coating and Passivation team is responsible for the Instruments Development Laboratory at the Fraunhofer CSP. We support interested partners in developing and marketing of processes and instruments and have experience in defining and realizing standards.

Services

  • Plasma texturing of silicon and glass surfaces
  • Thin-film deposition by means of PECVD and characterization of the layer (thickness, refraction index, chemical composition, ...)
  • Examination of the degradation and regeneration induced by light and charge carriers; development of regeneration processes
  • Measuring the carrier life time of silicon materials including sample preparation and passivation (AlOx, SiNx)
  • Development of instruments and standards

Examples

© Fraunhofer CSP

REM image of a plasma texture after silicon-nitride deposition in plan view.

© Fraunhofer CSP

Measured global reflection, transmission and absorption of a plasma texture as a function of the wavelength.

Maskless Plasma Texturing of Solar Cells with SF6 and O2

Reducing reflections is a basic requirement to achieve a high efficiency solar cells. For this reason, a technology for the plasma texturing of solar cells is being developed at the Fraunhofer CSP in order to further improve their properties. Plasma texturing produces nanostructures on the surface of silicon which reduce the reflection of incident light to an extent that the solar cell appears to be black for the observer. The maximum power of solar modules in the field can be further improved this way. Concomitantly, plasma etching enables the texturing of so-called kerf-less wafers which will gain more significance in industrial manufacturing in the years to come because of their cost-saving production.

light induced degredation
© LayTec

The LID Scope already permits testing on cellular level how high the power losses due to LID will be.

LID Test for Silicon Solar Cells

PERC technology is the high-flyer in photovoltaics: PERC solar cells with passivated rear surface, have a transformation efficiency which is significantly higher than that of standard cells and are continually gaining more and more market shares. However, PERC modules made of multi-crystalline silicon pose a substantial challenge: power losses occur due to light-induced degradation (LID). The LayTec company in Berlin offers LID Scope, an instrument that enables an easy, fast and flexible quality control for this this defect already on cell level. The measurement technique developed at the Fraunhofer-Center for Silicon Photovoltaics CSP can also be applied to all light-induced degradation effects in silicon solar cells.