Cadmium Telluride
Properties
| State | Solid (crystalline) |
| Color | Dark gray to black |
| Solubility | Insoluble in water and dilute acids; soluble in concentrated oxidizing acids |
| Melting Point | 1041 °C |
About Cadmium Telluride
Cadmium telluride sits almost exactly at the Shockley-Queisser optimum for single-junction solar conversion. The direct bandgap is 1.44 eV at 300 K against a theoretical optimum of 1.34 eV; the Shockley-Queisser limit at the CdTe gap is 32%, basically tied with silicon's. What makes CdTe industrially decisive is the absorption coefficient: above the bandgap CdTe absorbs at roughly 10⁵ cm⁻¹, two orders of magnitude higher than crystalline silicon, which means a CdTe absorber 2 µm thick captures 90% of the AM1.5 photons it needs while a silicon wafer requires 200 µm — a hundredfold material difference that translates directly into manufacturing cost. CdTe crystallizes in the cubic zinc-blende structure with tetrahedral coordination of Cd and Te, melts at 1041 °C, and is grown commercially by vapor transport deposition or close-spaced sublimation at module-line speeds. First Solar produces over 10 GW of CdTe modules per year, and CdTe leads all single-junction commercial PV technologies on production-line cost per watt and on energy-payback time (under 8 months in most climates). The same CdTe is the absorber in CdTe/perovskite and CdTe/Si tandem cells now under commercial development. Outside photovoltaics, single-crystal CdTe is the workhorse material for room-temperature x-ray and gamma-ray spectroscopy detectors — it has high atomic number for stopping power, a wide bandgap for low leakage current at 300 K, and resolves photopeaks well enough that medical CT manufacturers (Siemens, Philips) build photon-counting CT detectors out of it. CdTe is also the substrate for HgCdTe (mercury cadmium telluride, "MerCadTel") infrared focal-plane arrays used in F-35 targeting pods and the James Webb Space Telescope's near-infrared instruments.
Where you'll encounter it
If you've ever walked past a utility-scale solar farm in the desert Southwest US, roughly half of those modules are CdTe — First Solar's Series 6 and Series 7 panels in particular. In a spectroscopy lab, a CdTe or CdZnTe detector mounted on a portable XRF gun is what archaeologists and conservators use for non-destructive elemental analysis on paintings, artifacts, and ore samples; the detector resolves K-α lines down to the percent level without cooling. In a hospital that's installed photon-counting CT (a technology that hit the clinic in 2021–2022), the detector array is CdTe or CdZnTe single-crystal pixels — the move from energy-integrating Si scintillator detectors to direct-conversion CdTe is the technical basis for that whole imaging upgrade.
Common Uses
- Absorber layer in thin-film CdTe photovoltaic modules (First Solar Series 6/7)
- Bottom cell in CdTe-perovskite and CdTe-silicon tandem solar architectures
- Room-temperature x-ray and gamma-ray spectroscopy detectors for portable XRF and photon-counting CT
- Substrate for HgCdTe infrared focal-plane arrays in defense and astronomy
- Electro-optic Pockels modulators for 10 µm CO2-laser systems
Safety Information
Toxic, mutagenic, and carcinogenic by virtue of its cadmium content. GHS H301+H331 (toxic if swallowed and if inhaled, Category 3), H340 (mutagenic), H350 (IARC Group 1 carcinogen, cadmium and compounds), H361 (suspected reproductive toxicity), H410 (very toxic to aquatic life). OSHA PEL 5 µg/m³ as Cd. CdTe is far less bioavailable than soluble Cd salts — the lattice energy is high, leaching rates from intact crystalline CdTe in physiological fluids are nanomolar, and life-cycle analyses show CdTe modules actually reduce atmospheric Cd emissions versus the coal-fired electricity they displace. First Solar runs a closed-loop recycling program with >90% material recovery; modules are RoHS-compliant under the finished-PV-product exemption.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.