Coating Measurement of Solar Cells

Total Reflectance, Color and Layer Thickness of Coated and Uncoated Silicon Solar Wafers

The surface texturing of crystalline solar cells plays an important role to achieve high solar cell efficiencies. The texturing reduces reflectivity losses significantly and has a strong impact on the passivation of the cell. In addition to the texturing process step itself, the quality of the silicon material and the wafer sawing process have impact on the texture. Therefore, it is essential to gain detailed knowledge of the texturing. This knowledge and process control can be achieved by precise measurement of the total reflectance of the textured cells. Our Helios LAB-rc is the perfect tool to measure, analyze and optimize the widely used chemical texturing processes. It measures the total reflectance of bare and coated solar wafers, as well as the color and layer thickness of coated solar wafers.

Measurement of the Total Spectral Reflectance

Measurement of the total spectral reflectance is a good and accepted method for maintaining a stable texturing process. The texturing affects the average level of the Reflectance and also the amount of spread/variation of the Reflectance over the

wafer. Both, the average Reflectance level and the variation of the Reflectance over the wafer, are important and need to be controlled.

Functions of Helios LAB-rc

Helios LAB-rc is an easy to use manual measurement system that enables you to measure the total reflectance of polished and textured solar wafers. In addition it measures the color and the layer thickness of coated wafers.

  • Single-point measurement √
  • Integral total spectral reflectance measurement √
  • Wavelength and reflectance value at lowest reflectance √
  • Reflectance at user-definable wavelength √
  • Coating layer thickness √
  • User-definable quality limits √
  • Good / Bad indication √
  • Integrated fixed reference √
  • Average Reflectance within a selectable wavelength interval √
  • Color evaluation √
  • Manual single axis table √
  • Manual full wafer mapping √

Highlights of Helios LAB-rc

Measurement of bare and coated Wafers
  • Offline
  • Contactless and non-destructive
  • Static point by point measurement


Measurement Parameters
  • Total Reflectance: r (integral)
  • Color: c (Lab, xyY, …)
  • Layer Thickness: t (for coated wafer)
Works for all relevant Wafer Types
  • mc-wafers (polished, rough or textured)
  • pc-wafers (polished, rough or textured)
  • 125x125mm / 156x156mm / round / others
Works for all relevant Types of Textures
  • Isotropic chemically etched
  • Anisotropic chemically etched
  • RIE (Reactive Ion Etched)
Easy Operation
  • Integrated reference standard
  • Manual single-axis table for full wafer mapping
  • Easy line scan



Inline measurement of SiN coating thickness and refractive index on solar wafers direct after the coating process



Inline gap distance control of Silicon melt and heat shields in crystal pullers