Reflectance Spectroscopy

In a fraction of a second, the photovoltaic (PV) reflectometer measures the reflectance spectrum of a wafer or cell that is dimensionally within 6 in. × 6 in.

The measured reflectance plots are deconvolved to derive physical parameters, including surface roughness and texture, antireflective coating thickness, metallization area and height, and backside metallization properties.

Pair of drawings showing how direct normal incident light reflects in a scatter from a rough surface and some scattered incident light to a spot reflects directly normal.

The reflectance measurement uses a principle of reciprocity

Schematic of the PV Reflectometer system. A hollow sphere houses light sources (top), a sample stage (bottom), and sensing equipment (top). A diode array spectrometer is at the lower right, with a computer at the upper right.

A schematic of the reflectometer

PV Reflectometer graph showing reflectance vs. wavelength for silicon PV wafers at three stages: texture-etched (highest), sawed and cleaned (slightly lower), and anti-reflection coated (lowest, especially from 500–800 nm).

Reflectometer results on three groups of commercial PV-Si wafers (4.5 in. × 4.5 in.) at different stages of solar cell processing.
antireflective (AR) coating thickness: 794 to 858 Å

PV Reflectometer graph of reflectance vs. wavelength for silicon PV wafers at four stages: sawing (highest), texturing (lower), oxide coating (slightly lower), and anti-reflection coating (further reduced, especially at shorter wavelengths).

Reflectance curves (in arbitrary units) of 5-in. × 5-in. wafers taken with the PV-Reflectometer. These data yield information on the surface roughness, texture height, and oxide and AR coating thicknesses.
AR coating thickness: ˜600 Å

Andrew Ferguson

Group Manager, Spectroscopy And Photoscience

[email protected]
303-384-6637