Cell characterisation:
For process engineers and managers in depth understanding of quality control and optimization through cell characterisation is a key competence.
The courses offered by the Solar Academy include practical instructions on the following characterization equipment and techniques:
Sherescan:
The resistance, uniformity and reproducibility of the emitter layer plays a major role in achieving high solar cell efficiencies.
Determination of the emitter sheet resistance across the surface of a wafer, and studying the reproducibility from wafer to wafer is essential in optimizing
the emitter diffusion process. The Sherescan measures the resistance by means of a four point probe contact. It allows for mapping of the entire wafer surface.
Trainees will study wafers with different sheet resistances and learn the relation between the resistance and diffusion parameters.
Corescan:
Corescan is used for surface mapping of contact resistance between the emitter and the metallization grid of solar cells.
It is also possible to map the shunt resistance, short circuit current (LBIC) and open circuit voltage (Voc):
- Corescan
Map the contact resistance to optimise the metallisation process.
- Shuntscan
Locate shunts on solar cells.
- Voc scan
Find the locations of increased recombination.
- LBIC scan
Find the regions on a solar cell with lower bulk lifetime, optimise gettering and hydrogen passivation.
During these measurements, the trainees will practice operating the corescan machine and learn how the contact resistance, local shunts and current values can be related to the cell processing.
FT-IR:
The FTIR allows for determination of the carbon and oxygen concentrations in the wafers, and for the quality of the anti-reflection coating.
Trainees will be taught the relation between the silicon:nitrogen ratio and the properties of the ant-reflection coating.
Spectral response:
The home built spectral response unit measures SR in the spectral range of 300-1100 nm. White bias light (near 0.5 Sun, with varying intensity) can also be applied.
Trainees will study the external quantum efficiency (EQE) of solar cells as a function of wavelength, and learn how this effects the performance of solar cells and how cells might be improved. Spectral response measurements combined with reflectance will also yield the internal quantum efficiency (IQE).
Reflectance:
Reflectance measurements are performed using an integrating sphere set-up, also in the wavelength range 300-1100 nm.
This data is combined with spectral response to yield the IQE. Trainees will also study cells with different type of texturing and different thickness of the anti-reflection coating to determine the effect on the reflectance minimum.
I/V curves and Suns Voc:
With I/V curve measurements, the efficiency of solar cells can be determined.
Trainees learn how the I/V curve also yields information on series resistance and how this effects cell performance. These measurements are complimented by measurements of the Suns Voc to determine how this series resistance affects the measured Voc values.
Lifetime:
The lifetime of free carriers is determined by the amount of defects such as contaminations and microcracks.
Trainees will learn how these are related, and how the cell processing and wafer quality influence the amount of defects.
Contact quality:
Besides measurements of the contact resistance on the Corescan, the contacts are visually inspected by a microscope.
This way, width, height and the smoothness of the printed contacts are determined. The resistance of the finger contacts is measured by a bus bar to bus bar set up
and related to the width and height of the contacts.