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Tellurium is rare on Earth but it apparently exists in (relative) abundance elsewhere in the Solar System.
This topic is offered for NewMars members who might wish to contribute to a store of knowledge about this remarkable element.
We'll open with a Gemini report which followed a long series of exchanges about the First Solar company, which has survived completion with China despite being a US based company, by taking the risk of making solar panels with Tellurium.
I was hoping you would cover recycling. Thank you for including that important part of the report, as well as for describing the ongoing effort to obtain the maximum possible performance from the smallest possible quantity of this resource. The chemical and physical properties of Tellurium must be unique, or some other element would have been enlisted to perform this important function.
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The physical and chemical properties of tellurium (Te) make it uniquely suited for thin-film photovoltaics. Other compounds exist—such as Copper Indium Gallium Selenide (CIGS) and emerging perovskites—but none match the balance of physics, durability, and commercial manufacturability that cadmium telluride (CdTe) provides.
First SolarThe distinct characteristics that make CdTe so difficult to replace include:
1. The Ideal Bandgap for Sunlight
In solid-state physics, the energy bandgap determines which wavelengths of light a semiconductor can absorb and convert into electricity. According to the Shockley-Queisser limit, the theoretical maximum efficiency for a single-junction solar cell occurs at a bandgap around 1.34 eV to 1.5 eV.
Silicon sits at roughly 1.1 eV, which is slightly lower than ideal.
Cadmium Telluride possesses a direct bandgap of 1.45 eV to 1.5 eV. This almost perfectly matches the energy spectrum of sunlight hitting Earth's surface.
Max-Planck-Institut für Eisenforschung (MPIE)
2. Extreme Light Absorption (Direct Bandgap)
Silicon is an indirect bandgap material, meaning a photon needs to interact with crystal lattice vibrations (phonons) to generate an electron-hole pair. Because this is less efficient, silicon wafers must be relatively thick (roughly 150 to 200 micrometers) to catch incoming light.
CdTe is a direct bandgap semiconductor with an extraordinarily high optical absorption coefficient (>10 4 cm −1 for solar wavelengths). It absorbs over 90% of photons within a layer just 1 to 2 micrometers thick—about 1/100th the thickness of a silicon cell. This microscopic layer requirement is why thin-film factories can run so fast and use so little raw material per panel.
Max-Planck-Institut für Eisenforschung (MPIE)
3. High Chemical & Thermal Stability
Unlike organic semiconductors or perovskites (which degrade rapidly when exposed to moisture, oxygen, or heat), CdTe forms a robust, resilient crystal structure. It retains high electrical performance even under elevated operating temperatures in desert environments, where crystalline silicon panels suffer significant heat-related efficiency drops.
4. Vapor Deposition Behavior
From a manufacturing engineering standpoint, CdTe is uniquely easy to deposit. It sublimes (transitions directly from solid to gas) at manageable temperatures and re-condenses uniformly onto glass superstrates. This property enables vapor transport deposition at high speeds across massive glass sheets, replacing complex cell-assembly steps with continuous processing.
What would you like to do next?
Explore Shockley-Queisser limit physics for single-junction solar cells
Compare direct vs indirect bandgap semiconductors in optoelectronics
Review electrochemically enabled recycling methods for CdTe modules
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