Cadmium Telluride (CdTe)

• The manufacturing process of cadmium telluride material

1. Raw material preparation: Select high purity tellurium powder and cadmium powder as raw materials, the purity is usually required to be greater than or equal to 99.999%, mixed according to the stoichiometric ratio (1:1), to ensure the adequacy of the reaction and the uniformity of the product, which is the basis to ensure the performance of cadmium telluride materials.
2. Synthesis process:

Pressurized smelting method: Tungsten (TE) and cadmium (CD) are mixed and smelted under 450~500℃,0.4~0.6MPA pressure, and then purified by vacuum purification. This method reduces the reaction temperature by pressurization, has high utilization rate of raw materials, and the purity of product can reach 99.999%. After cooling, CDTE crystals are generated.

Fusion Reaction Method: In a sealed quartz tube, cadmium ingots and crushed tellurium materials are alternately layered and loaded. The fusion reaction is achieved through staged temperature control (600~1200℃). A carbon film is applied to the inner wall of the quartz tube to prevent cadmium from reacting with quartz, and vacuum deoxidation is used to enhance purity. This method does not require raw material grinding and is suitable for high-purity (6N grade) production

Wet precipitation method: Using cadmium salt and tellurium oxide as raw materials, the precursor is precipitated by ammonium carbonate, and then cadmium telluride powder is synthesized by heat treatment (300~550℃) in a hydrogen and argon mixed atmosphere. This method avoids high temperature and pressure and grinding pollution, is suitable for industrial continuous production, and has high safety

Laser vapor deposition: In a high vacuum environment, the substrate (500~600℃) is heated by laser, and the vapor of tellurium and cadmium is deposited to form a film under the drive of carrier gas. This process has low energy consumption and high purity, which is suitable for large-scale preparation of photovoltaic thin films, and the raw materials can be recycled

3 Follow-up:

Vacuum purification: The cadmium telluride crude product obtained by smelting is purified under vacuum to further improve its purity.

Modification: In order to improve the photoelectric performance of cadmium telluride materials, multi-walled carbon nanotubes and cadmium chloride can be used for modification.

Elements such as chlorine (CL) or copper (CU) are doped to optimize the electrical performance of CDTE; surface modification or nanostructure design is used to improve the photoelectric conversion efficiency.

Heat treatment: The precursor powder is heat treated in a mixed atmosphere to form a stable cadmium telluride target.

4. Post-treatment process

Solar cells or detectors are manufactured using lithography, etching and other processes.

Annealing treatment: eliminate crystal defects and improve material stability

• Technical index advantages

1. High photoelectric conversion efficiency

The efficiency of the small area battery in the laboratory is 22.1%, and the mass production efficiency of the module is about 19%. The theoretical limit efficiency can reach 32%.

The absorption coefficient is high (about 10⁵ CM⁻¹), and only 1~2 micron thick film is needed to absorb more than 90% of visible light, with low material consumption.

2. Excellent stability and durability

After 27 years of operation in the outdoor environment, the efficiency only decreased by 12%, which is better than the 20% attenuation rate of crystalline silicon components.

The temperature coefficient is low (-0.25%/℃), the power generation loss is small in high temperature environment, and it can adapt to extreme climate such as desert.

3. Adaptability to low light environment

It can maintain high power generation efficiency even under cloudy or low light conditions, and is suitable for cloudy areas and building shadow environment applications.

4. Environmental protection and low cost

The manufacturing process is simplified (such as gas phase deposition without high temperature sintering), and the energy consumption is reduced by 30%~40% compared with crystalline silicon cells.

The material consumption is small, the unit power generation cost is low, and the production process has no harmful waste.

5. Customization and aesthetics

The color, light transmittance and shape can be flexibly adjusted to meet the aesthetic requirements of photovoltaic building integration (BIPV), suitable for glass curtain wall and roof integration.

• Industry applications

1. Solar cells

High photoelectric conversion efficiency: the highest efficiency in the laboratory is 24.2% (2023 data), close to monocrystalline silicon (26.7%), and the theoretical limit is higher (~30%).

Broad spectral response: band gap 1.45 EV, covering visible to near infrared bands, suitable for weak light environment.

Low cost manufacturing: the film thickness is only a few microns, the material consumption is less, and the energy consumption is lower than that of crystalline silicon cells.

Flexible and lightweight: can be deposited on plastic or metal foil, suitable for wearable devices and building integrated photovoltaic (BIPV).

2. Large photovoltaic power stations

With low cost and high stability, it is suitable for the construction of desert power stations. In 2023, the global production of cadmium telluride components exceeded 11GW, with an annual growth rate of more than 10%.

3. Special device manufacturing

It is used in infrared detectors, X-ray sensors and light-emitting devices, because its wide band gap (1.45 EV) characteristics are suitable for a variety of photoelectric conversion scenarios

4. Infrared detector

High sensitivity: excellent response to medium and long wave infrared (3-14 ΜM), suitable for night vision, security and thermal imaging.

Fast response time: up to nanosecond level, better than traditional materials (such as HGCDTE).

No refrigeration: it can work at room temperature, reducing system complexity and cost.

•  Challenges and Development Trends

1. Essential problem: CD is a heavy metal, so the pollution in the production process should be strictly controlled and environmental protection recycling technology should be promoted.

2. Efficiency bottleneck: the current commercial efficiency (17-20%) is lower than the laboratory level, and interface engineering and defect management need to be optimized.

Emerging directions:

Stacked cells (such as CDTE/CIGS) improve efficiency to more than 25%.

Quantum dot technology enhances light absorption and carrier separation.

With its high efficiency, low cost and versatility, CDTE occupies an important position in photovoltaic and infrared detection fields. In the future, it will further expand its application prospects by breaking through the bottleneck of process optimization and environmental protection technology, especially in flexible electronics and clean energy fields.