Solar module imaged with the Andor Luca-R Electron Multiplying CCD (EMCCD) camera.

With demand for
photovoltaic panels more than doubling year on year, manufacturers are under
pressure to increase solar cell efficiency, improve production yields, and
build capacity. Now, a joint team from the Department of Electrical and
Computer Engineering at the National University of Singapore has demonstrated a
novel technique to non-destructively test silicon wafer solar cells.

In their research, PhD
student Matthew Peloso and his colleagues are developing methods of
characterizing solar cells based on luminescence detection and relating this to
the electrical properties of the devices. They use an Andor Luca-R Electron
Multiplying CCD (EMCCD) camera to image the solar cells and believe the process
may be integrated into the production process, helping manufacturers to improve
yields and ramp up volume.

“We have shown that by
controlling the applied voltage inducing electroluminescence in solar cells,
the observed spectrum of emitted radiation may be used to identify particular
performance-reducing defects,” says Peloso. “Detection of these changes can be
used to understand the electrical properties of defects in the wafers and,
potentially, to study their origin, which may lead to lower-cost,
higher-quality materials for production. Moreover, the method has proven useful
at the module as well as the cell level. We demonstrated that breakdown
luminescence—which we believe is associated with metallic impurities—does not
show a one-to-one relationship with other defect related luminescence signals
detected at energies below the silicon bandgap. Interestingly, certain defects
did not lead to electrical shunts, which may cause irreversible destruction of
PV modules and cells.”

“We chose the Andor Luca-R
EMCCD camera because of its high red to NIR sensitivity and linear response to
intensities, which allows more quantitative data acquisition. The electron
multiplying (EM) gain control allowed us to enhance signal to noise when
necessary, although we operated much of the time in non-EM gain mode. The
Luca-R also provides a good balance of attractive features, including the
ability to achieve high integration times and binning, at a lower price
compared to other available scientific cameras, such as deep depletion CCD
cameras,” he adds.

Colin Coates, Imaging
Product Manager at Andor, comments that “Andor’s Luca R makes ultrasensitive
EMCCD technology available to this price sensitive application. The megapixel
format, enhanced red sensitivity and ability to apply EM gain as required
renders Luca R an extremely attractive and versatile camera for
characterisation and in-line testing of photovoltaics by electro and
photoluminescence.”

Andor,
www.andor.com