In the 1980s, while still at the Fraunhofer Callab, we have been involved in the design and development of the cell housing for the World Photovoltaic Scale (WPVS), which is a result of several measurement round robins among the major calibration laboratories for solar cells and modules.
In this tradition, Optosolar offers a variety of reference cells for measurement of light, be it for IV characteristics of solar cells and PV modules, or for spectral Response measurements.
Reference cells for IV calibrations:
For easy use, they come in their standard configuration with a shunt resistor. So their measurement signal is mV/ (1000 W/m2), and they can directly be used on any voltage measuring input. We can also equip these cells with Kelvin (4 Point) contacts, so that their full IV can be measured.
Reference cell size: 2cm/1 inch 2 inch 6 inch.
The 2cm cells are mounted in a WPVS (World Photovoltaic Scale) - like housing which enables cooling of the cell. They are typically chosen for indoor laboratory measurements.
(K. Buecher has co-authored the investigation and publication for the WPVS, see e.g World Photovoltaic Scale ).
The 6 inch cells are encapsulated module like. They are good references for indoor and outdoor module measurements, as their encapsulation has similiar properties to an encapsulated module.
The reference cells come with a PT 100 for temperature measurement.
All reference cells calibrations can be certified to ISO 17025.
Spectral Filtering of Reference cells
The cells can come with filtering to adapt to a variety of new solar cell materials. Whereas some manufacturers offer 'super' reference cells with a spectral mismatch correction of nearly 0, we do not advertise this.
The true reason is, that, according to the Standard IEC 60904-7, a spectral mismatch correction needs to be applied to any measurement. It can be omitted if the mismatch correction is near 0. But now, the mismatch correction is a function of sun spectrum, simulator spectrum, reference cell spectral response and sample spectral response. Even if you order a reference cell with mismatch correction 0, this will be true for only one spectral response shape in your solar simulator. But, your cell development lives from varying your cells to optimise them from your starting point. So it will be your intention to vary the cells as much as possile for optimisation, and you might move away from the optimal spectral response shape that had been advertised for mismatch 0. Then, you will need a spectral mismatch correction. We can give special training how this is done and when it is necessary.
To be more clear about this: we offer reference cells with very good spectral matching. We also give trainings how to use these to obtain highest measurement precision.
Quality test of equipment
Using a spectrally mismatched cell is a really good test to verify the precision of all your testing Equipment.
Did you ever calibrate a Silicon cell, using a GaAs reference cell? Maybe even to a precision of 1-2%?
Those two cells are probably as badly spectrally matched as it could be: the Silicon cell sees light from 300nm to 1100nm, the GaAs cell is 'blind' for the solar simulator light above 900nm.
Doing that type of calibration is an indication of the quality of your spectral response measurement, your solar simulator spectrum measurement and the overall measurement technology and bias. If you have very good control and quality measurement of all these quantities, you may even reach a precision of 1% in short circuit current with the mismatched reference cell. -To achieve such a precision needs very good control of all your measurements - we can train you to obtain that.
To be clear about it: we recommend to use a well matched reference cell for any measurement.
The method described above, in contrast, can be used as an audit and a qualification of your measurement processes in general.
Reference Cells for Spectral Response, ICPE, IQE, EQE and DSR
We offer reference cells for all measurements in monochromatic light. This covers the full spectral range between 200nm and 3000nm.
Typical configurations are:
Silicon reference cell, 300nm - 1160nm
Germanium reference cell, 800nm - 1800nm
IR reference cell, up to 2200nm / 2600nm / 3000nm
UV reference cell, starting at 200nm.
We use special detectors with highest stability, linearity and uniformity to the best of currently available technical performance.
Our Silicon detectors have high responsivity in the UV, they are linear and uniform over nearly all their area to ca. 1%.
For Research Systems, we offer detectors with 10mm (square/circular) area.
For Budget applications, we can offer 5mm and 3mm variations.
The detector housings come with a PT 100 for temperature measurement.
for more information, please see pdf: Reference Cells
for data logging of reference cells, pyranometers, PV modules, please see pdf: Photovoltaic Dataloggers