Technical information
Crystalline silicon wafers remain the material of choice
for photovoltaic modules, accounting for 90% of the photovoltaic (PV)
market. However, the cost of the silicon remains a major barrier to reducing
the cost of crystalline silicon photovoltaics. SLIVER® uses a new
technique to produce thin single crystal silicon solar cells.
The new technology allows for large decreases in silicon usage compared to conventional
crystalline silicon wafer technologies. In addition, it allows for a large reduction
in the numbers of wafers processed per module by up to a factor of 35 compared
to standard crystalline silicon technology.
The new SLIVER cell process uses a micromachining technique to form deep narrow
grooves perpendicular to the wafer surface. The grooves are typically less than
40 microns in width after micromachining through the thickness of a 1- 2mm thick
silicon wafer. The result of this micromachining is a large number of thin (50
microns) silicon strips in the centre of the wafer, held together by the unetched
surrounds of the wafer. On 1-2mm thick, 150mm diameter wafers, these strips typically
are approximately 1000mm long, 1mm wide (wafer thickness) and 50 micron thick.
The SLIVER cells are constructed on the narrow strips of silicon formed during
the micromachining. Cell processing is completed while the silicon strips are
still supported by the silicon substrate at the edge of the wafer.
The SLIVER cells are capable of excellent performance due to their thickness
and good cell design with demonstrated efficiencies over 19% and voltages of
680mV. In addition, the cells are bifacial (accepts light from either sides)
and very flexible. With a thickness of only 50 microns, this corresponds to a
1600 Watt/Kg ratio. Unlike conventional cells, SLIVER cells have a width that
is of the order of the thickness of the module. This allows for the design of
efficient light trapping schemes.
A simple design approach is to introduce a diffuse reflector to the rear of a bi-glass module, in which the cells are positioned keeping a significant space between them. The light striking between two cells is scattered from the rear reflector and is internally refracted directed onto the rear surface of the bifacial SLIVER cells. Several prototype SLIVER modules have been fabricated with silicon coverage fraction of only 50% and were independently tested at Sandia National Labs, demonstrating a 12-14% efficiency.
Schematic of selectively etched wafer. Long thin silicon slices are supported
by the wafer frame. Please click on image to view a larger version.
1000cm2 SLIVER module. The cells are spaced with gaps equal to cell width and the module has a rear diffuse reflector.
SLIVER® is a registered trade mark of Origin Energy Solar.
Technical papers
Latest production developments in SLIVER technology
Reliability
testing of SLIVER modules and effects of partial shading on power output
High
performance characteristics of SLIVER silicon solar cells
Update
on the manufacturing of SLIVER cells and modules
Characterisation
of the thermal response of SLIVER cells and modules
Modelling
of SLIVER modules incorporating a lambertian rear reflection
Embodied energy of
SLIVER modules orientation on energy production
The
effect of bifacial SLIVER module orientation on energy production
SLIVER modules
- A crystalline silicon technology of the future
SLIVER cells for concentrator
systems