Transcript Cadmium-Telluride-Solar-Cells

Nurcihan AYDEMİR 080604046
Kürşad UYANIK 080604047
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Cadmium telluride (CdTe) is a crystalline compound formed from
cadmium and tellurium.
It is used as an infrared optical window and a solar cell material.
Cadmium telluride (CdTe) is a photovoltaic (PV) technology based on
the use of a thin film of CdTe to absorb and convert sunlight into
electricity.
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Best cell efficiency has plateaued at 16.5% since 2001 (a record
held by NREL). The opportunity to increase current has been
almost fully exploited, but more difficult challenges associated
with junction quality, with properties of CdTe and with
contacting have not been as successful.
Improved doping of CdTe and increased understanding of key
processing steps (e.g., cadmium chloride recrystallization and
contacting) are key to improving cell efficiency. Since CdTe has
the optimal band gap for single-junction devices, it may be
expected that efficiencies close to exceeding 20% (such as
already shown in CIS alloys) should be achievable in mass
produced CdTe cells.
In 2009, EMPA, the Swiss Federal Laboratories for Materials
Testing and Research, demonstrated a 12.4% efficient solar cell
on flexible plastic substrate.
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Cadmium Telluride (CdTe) has very low
solubility in water.
It is etched by many acids including
hydrocloric and hydrobromic acid, forming
(toxic) hydrogen telluride gas.
Fig. 1. Crystallographic orientation and (a1) Chemical
etching of the pure CdTe substrate.
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Available as a powder or as a crystal.
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CdTe photovoltaics is a technology that uses
the compound Cadmium Telluride (CdTe) as
the semiconductor material in photovoltaics
cell that convert sunlight into DC (direct
current) electricity.
Photovoltaic (PV) cells are an integral part of
solar electric-energy systems which are
becoming increasingly important as
alternative sources of utility power.
Fig.2. Structure of CdTe
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CdTe offers some advantages over crystalline
silicon (Si), the substance originally used in
the manufacture of PV cells.
A functional layer of CdTe can be made
extremely thin, on the order of a few
micrometers (units of 10-6 meter), far thinner
than a typical Si layer.
CdTe offers better efficiency than Si at high
temperatures and low levels of illumination.
Fig.3. Flexible CdTe Thin Film
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In addition, CdTe PV cells require less energy
to produce than Si PV cells do.
Cadmium (Cd) and Tellurium (Te) are both
products of zinc, copper and gold mining.
Fig.4. Solar panels equipped with CdTe
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Otherwise, some concern over the existance
of Cd in CdTe PV cells. Cadmium is a toxic
heay metal. However, the proponents of CdTe
technology point out that the compound does
not dissolve in water, so the elemental Cd
should not pose any hazard to aquifers.
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Cadmium is one of the top 6 deadliest and
toxic materials known. However, CdTe
appears to be less toxic than elemental
cadmium, at least in terms of acute exposure.
This is not to say it is harmless. Cadmium
telluride is toxic if ingested, if it’s dust is
inhaled, or if it is handled improperly (i.e.
without appropriate gloves and other safety
precautions).
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One study found that the highly reactive
surface of cadmium telluride quantum dots
triggers extensive reactive oxygen damage to
the cell membrane, mitochondria, and cell
nucleus. In addition, the cadmium telluride
films are typically recrystallized in a toxic
compound of cadmium chloride.
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Laboratory have found that large-scale use of
CdTe PV modules does not present any risks
to health and the environment, and recycling
the modules at the end of their useful life
resolves any environmental concerns.
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Ease of manufacturing: The necessary
electric field, which makes turning solar
energy into electricity possible, stems from
properties of two types of cadmium
molecules, cadmium sulfide and cadmium
telluride. This means a simple mixture of
molecules achieves the required properties,
simplifying manufacturing compared to the
multi-step process of joining two different
types of doped silicon in a silicon solar panel.
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Good match with sunlight: Cadmium telluride
absorbs sunlight at close to the ideal
wavelength, capturing energy at shorter
wavelengths than is possible with silicon
panels
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Cadmium is abundant: Cadmium is abundant,
produced as a by-product of other important
industrial metals such as zinc, consequently
it has not had the wider price swings that
have happened in the past two years with
silicon prices.