Harnessing the massive amounts of energy that reaches
the Earth from the Sun is a challenging but necessary step to ensure that the
future energy needs of the planet can be met. When light reaches a solar panel
or photovoltaic (PV) cell, it can either be reflected, absorbed or pass right
through it. At the heart of a solar cell is a semiconductor layer, which is
unequivocally the most important part of the cell.
Now make a solar panel by any semiconductor. The
researchers at Berkeley Lab have developed a new technology, which allows
manufacture of low-cost, high-efficiency solar cells using any semiconductor
material. This material combines the properties of metals and insulators to
yield a substance uniquely skilled at converting sunlight to electricity. When
the semiconductor absorbs light, photons transfer their energy to electrons
which flow through the material as an electrical current towards metal contacts
above and below the semiconductor layer, from where it can travel to the power
grid.
The new technology also known as Screening-engineered
field-effect photovoltaics or SFPV has opened the door for using inexpensive
semiconductors like metal oxides, sulfides and phosphides, which were
considered unsuitable some time ago. The efficiency of a PV cell is defined as
the amount of electrical power divided by the energy from sunlight in. The
amount of electricity is dependent on the quality of light offered – it’s
intensity and wavelengths – and the performance characteristics of the cell.
Physicist Alex Zettl said: “It’s time we put bad
materials to good use,” and futher Alex pointed out: “Our technology allows us
to sidestep the difficulty in chemically tailoring many earth abundant,
non-toxic semiconductors and instead tailor these materials simply by applying
an electric field.” Among the most efficient and by far the most common
semiconductor used is silicon which is found in approximately 90% of modules
sold. It was first used in solar cells in 1956 and is considered a key material
in solar energy production.
The researchers said that many abundant materials can
instead be tailored for solar power applications by applying an electric field.
A moderately screening top electrode allows the gate
electric field to amply penetrate the electrode and more uniformly modulate the
semiconductor carrier concentration and type to induce a p-n junction with SFPV
technology. “This enables the creation of high quality p-n junctions in
semiconductors that are difficult if not impossible to dope by conventional
chemical methods.”
SFPV effects in a self-gating configuration, where the
gate is powered internally by the electrical activity of the cell itself.
“The self-gating configuration eliminates the need for
an external gate power source, which will simplify the practical implementation
of SFPV devices. Additionally, the gate can serve a dual role as an
antireflection coating, a feature already common and necessary for high
efficiency photovoltaics.” Other cells focus sunlight onto PV materials using
mirrors or lenses. These concentration PVs (CPV) require less material as the
light is focused on a comparatively small area and have the highest overall
efficiency because the light becomes concentrated on one spot.
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