What is Cadmium Telluride? Definition, Advantages & Disadvantages

Cadmium Telluride (CdTe) is a stable crystalline compound utilized in thin-film solar technology to convert sunlight into electricity. This material is known for its good optical absorption and simplicity in manufacturing, allowing it to serve as an efficient semi-conducting layer in various solar cells.

The main advantages of Cadmium Telluride include its lower production costs compared to silicon-based panels, due to simpler manufacturing processes and the use of less raw material. Additionally, CdTe cells are lighter and offer greater flexibility, making them suitable for a range of applications beyond solar panels, such as building materials or vehicles. CdTe cells demonstrate efficient sunlight absorption thanks to their direct bandgap, which is closely aligned with the optimal range for converting solar energy, allowing for thinner layers and material savings.

However, Cadmium Telluride presents a few disadvantages. Among the main drawbacks of CdTe cells are the lower efficiency levels compared to traditional silicon cells and concerns regarding the environmental impact due to the toxicity of cadmium. Additionally, the limited availability of tellurium, a less common element, affects the production of CdTe panels.

In terms of efficiency, CdTe solar cells have demonstrated conversion rates beyond 22% under lab conditions, with commercial modules averaging around 18-19%. While this is lower than the highest efficiencies seen in silicon cells, it remains competitive within the thin-film solar cell market. Continued improvements in cadmium telluride technology are pushing closer to CdTe’s theoretical efficiency of above 30%.

Regarding costs, CdTe solar cells are generally cheaper to produce than silicon-based cells, with prices around $0.46 per watt. This is significantly less than the cost of crystalline silicon panels, making CdTe an attractive option for large-scale solar energy production despite its lower efficiency.

What is Cadmium Telluride?

Cadmium telluride (CdTe) is a stable crystalline compound formed from the elements cadmium (atomic number 48 on the periodic table) and tellurium (52 on the table). Cadmium telluride is used in thin-film technology in the solar power industry to form a semiconducting layer that acts to convert sunlight into electricity. CdTe uses one or more layers of photovoltaic (PV) cells arranged on a substrate, which is metal, plastic, or glass. Solar or photovoltaic cells (“photo” meaning light, “volt” meaning electricity) are made up of semiconductor material such as CdTe that absorbs the photons, or particles of solar energy found in sunlight and then converts this energy into electricity. There are different types of thin-film PV cells.

Most thin-film solar cells, including those made from CdTe, belong to the "second generation" of solar technologies, which depart from traditional silicon-based cells like monocrystalline and polycrystalline. These second-generation “thin film” cells use alternative materials that aim to reduce manufacturing costs and improve the versatility of solar cells. Second-generation cells like CdTe are made using thinner layers of materials and are less expensive to produce than their silicon counterparts. Though less efficient than monocrystalline cells, thin-film cells offer a compelling alternative due to their lower cost, lighter weight, and greater flexibility.

What is Cadmium Telluride made of?

The compound cadmium telluride is made of two elements, which are cadmium and tellurium. Cadmium is a soft, silvery-white metal that shares similarities in chemical properties with mercury and zinc. Tellurium is a metalloid that combines metallic and non-metallic properties, presenting as a brittle, rare, and slightly toxic element.

Typically, cadmium is sourced from the byproducts of zinc, lead, and copper ore mining and processing. A notable characteristic of cadmium is its malleability and ductility, allowing it to be easily shaped. This metal belongs to the transition metals category, indicative of its propensity to form various compounds.

Tellurium is chemically related to sulfur and selenium, reflecting varied elemental behavior. In the Earth's crust, tellurium's abundance is quite low, akin to that of platinum, making it one of the less common elements. This rarity extends to its natural occurrence, predominantly found within specific mineral ores like sylvanite and calaverite.

The combination of cadmium and tellurium forms cadmium telluride (CdTe), a crystalline compound extensively used in photovoltaic cells for transforming solar energy into electricity. The efficiency of CdTe in this conversion process is largely due to the specific, inherent characteristics of its components. Cadmium offers high electrical conductivity, while tellurium contributes to the material's ability to absorb light and convert it into electricity – a property essential for photovoltaic function.

In the structure of solar cells, cadmium telluride is applied in thin layers. These layers are crucial as they create the junction where sunlight is converted into electrical energy. The layering within cDTe cells is significant because it allows for the precise control of electrical and optical properties, ensuring that photons from sunlight are efficiently absorbed and converted into electrons, which then generate electricity.

How does Cadmium Telluride work?

Cadmium telluride (CdTe) works by forming an electric field that converts light absorbed in the CdTe layer into current and voltage. Cadmium telluride (CdTe) functions as the primary photoconversion layer in various applications, notably in photovoltaic (PV) or solar cells. The main purpose of CdTe within these cells is to convert sunlight into electrical energy efficiently. This process begins when the CdTe film, applied as a thin layer to a substrate like glass, absorbs visible light. The absorption occurs primarily within the first micron of the material, highlighting the efficiency of CdTe in capturing solar energy.

Once the CdTe layer absorbs sunlight, it generates electron-hole pairs. These are crucial for electricity production as they contribute to the creation of an electric field within the solar cell. This electric field is formed when the CdTe layer is sandwiched between layers of different materials, typically including a layer of cadmium sulfide (CdS) and a back contact, which vary in composition depending on the specific cell design.

The thickness of the CdTe thin film in a solar cell is notably thin, roughly comparable to the thickness of ten sheets of paper. Despite its slimness, this layer is remarkably effective at photoconversion. The electric field generated across the CdTe layer separates the electron-hole pairs: electrons are driven towards one side, while holes (the absence of electrons) move towards the opposite side. This movement creates current, and when the circuit is completed, for instance, through busbars and wires attached to the layers, this current can be captured and used as electricity.

In contrast to traditional solar panel technologies, which rely on silicon wafers connected together, CdTe solar cells incorporate this semiconductor layer directly onto a pane of glass or another substrate, streamlining the structure and potentially reducing costs. Besides their significant role in solar energy conversion, cadmium telluride's properties make it useful in other applications, such as infrared detectors, X-ray detectors, and other semiconductor devices like transistors and diodes. Each application exploits the unique ability of CdTe to absorb and convert different forms of energy, whether it is sunlight, infrared light, or X-ray radiation, into usable signals or power.

Is Cadmium Telluride effective for solar panels?

Yes, cadmium telluride (CdTe) is an effective material for thin-film solar panels. However, its commercial efficiency, typically around 16-19%, is lower than that of monocrystalline panels, which currently approaches 25%. The lower efficiency of CdTE cells currently limits their commercial viability compared to traditional silicon panel types like monocrystalline. The current efficiency of commercially available CdTe solar panels is 18.6%, while lab-based efficiency rates exceed 22%, according to a paper published in 2023 in “Solar Energy Materials and Solar Cells.” The paper, entitled “CdTe-based thin film photovoltaics: Recent advances, current challenges and future prospects”, was written by Michael A. Scarpulla, Brian McCandless, Adam B. Phillips, Yanfa Yan, Michael J. Heben, Colin Wolden, et al.

A major milestone was achieved by First Solar in 2016 when a world-record 22.1% efficiency was achieved in the lab for their CdTe solar cells. CdTe cells have a theoretical efficiency of above 30%. With continual improvements, the efficiency of commercially available CdTe solar panels continues to bridge the gap between theoretical and actual.

The lower efficiency of CdTe means that solar panels made from this material will convert less sunlight into electricity than their silicon counterparts, which is a critical metric in evaluating the performance of solar technologies. Despite their relatively low efficiency, CdTe solar panels present several advantages. First, they have the benefit of much lower production costs compared to silicon-based panels. This cost-effectiveness is derived from simpler manufacturing processes and the use of less expensive materials, making solar energy more accessible and affordable, especially for large-scale installations. Second, CdTe panels have a significant advantage in terms of the speed and energy required for manufacturing. They are produced more quickly and with less energy than traditional silicon panels, contributing to a lower overall carbon footprint and making them a more sustainable option in the long run.

What are the advantages and disadvantages of Cadmium Telluride?

Cadmium telluride solar cells offer distinct advantages, including lower manufacturing costs, efficient absorption of specific wavelengths of sunlight, and the abundant availability of cadmium.

More information on the three main advantages of Cadmium Telluride is given below.

• Lower Manufacturing Costs: The production of cadmium telluride (CdTe) solar cells is simpler and more cost-effective compared to silicon-based solar panels. This simplicity arises from the process of combining cadmium sulfide and cadmium telluride to form the solar cell's active layers, which naturally establish the electric field essential for the conversion of solar energy into electricity. In contrast, manufacturing silicon solar panels involves a more intricate procedure. This includes creating silicon wafers, doping them with different impurities to form p-type and n-type silicon layers, and then carefully joining these layers to form a p-n junction. The doping and layering process in silicon manufacturing requires precise control and high temperatures, making it more complex and energy-intensive than the method used for CdTe solar cells.
• Efficient Absorption of Sunlight: Cadmium telluride (CdTe) solar cells possess a natural advantage as a material for solar panels in their efficient absorption of shorter wavelengths of sunlight. This characteristic enables CdTe panels to utilize a significant portion of the solar spectrum efficiently. However, silicon solar cells generally have higher conversion efficiencies than CdTe because they are better at converting the absorbed light into electricity. While CdTe cells excel in capturing energy from specific parts of the spectrum (notably, the shorter wavelengths), silicon cells perform consistently across a wider range, including both shorter and longer wavelengths.
• Cadmium is Abundant: The cadmium used in CdTe cells is a by-product of mining metals like zinc, which means it's more readily available and less subject to market fluctuations than silicon, which has experienced significant price swings.

The primary disadvantages of cadmium telluride solar cells include their lower efficiency in converting sunlight to electricity compared to silicon-based cells, the limited availability of the critical component tellurium, and the significant environmental and health risks associated with the toxicity of cadmium.

More information on the three main disadvantages of Cadmium Telluride is given below.

• Lower Efficiency Level: CdTe solar panels have an average efficiency of about 10.6%, lower than the typical efficiencies of 15-20% found in silicon solar cells. This lower efficiency means they convert less sunlight into electricity, requiring more panels for the same amount of power, which impacts the overall cost-effectiveness and land usage.
• Tellurium Supply: While cadmium is abundant, tellurium, the other critical component, is much rarer, found only in select parts of the world and primarily as a by-product of copper mining. The limited availability of tellurium could constrain the production of CdTe panels, impacting the scalability of this technology.
• Toxicity of Cadmium: Cadmium is a highly toxic material that poses environmental and health risks. The toxicity of cadmium poses risks of kidney, bone, and respiratory system damage, along with soil and water contamination if not properly handled and disposed of, especially when considering its use in large-scale solar installations. As a result, cadmium requires strict handling and recycling measures to mitigate these health and environmental risks.

What are the benefits of using Cadmium Telluride Solar Cells?

The main benefits of using cadmium telluride solar cells are related to their cost-efficiency and their versatility, which makes them suitable for a variety of substrates and surfaces. Further advantages of cadmium telluride solar cells are their efficiency in sunlight absorption and their low environmental impact. The four main benefits of cadmium telluride solar cells are explained in more detailed below.

• Cost-Efficiency: Cadmium Telluride (CdTe) solar cells are recognized for their cost-effectiveness, as they feature the lowest cost per watt among photovoltaic technologies. This affordability arises from lower production costs due to simpler manufacturing processes and less expensive materials. Additionally, CdTe panels have the shortest energy payback time, meaning they generate the energy used in their production faster than other types of solar cells, enhancing their overall economic value.
• Versatility: The versatility of CdTe solar cells is another significant advantage. They can be applied to a variety of substrates, including rigid glass and flexible materials like metal or plastic. This flexibility allows for a wide range of applications, from traditional solar panels to innovative uses such as integrating photovoltaic cells into building materials, vehicles, and portable devices. The ability to adapt to different surfaces and environments makes CdTe technology suitable for diverse installation scenarios.
• Efficient Sunlight Absorption: CdTe solar cells exhibit efficient sunlight absorption due to their direct bandgap, which is closely aligned with the optimal range for converting solar energy into electricity. Their strong absorption characteristics permit thinner photovoltaic layers, leading to savings on materials and further reducing production costs. Although they may have lower efficiency rates compared to silicon-based solar cells, CdTe cells maintain substantial performance under varying real-world conditions, such as fluctuating temperatures and low-light environments.
• Low Environmental Impact: The environmental impact of CdTe solar cells, while a concern due to cadmium's toxicity, is mitigated by several factors. On the one hand, CdTe cells have one of the lowest carbon footprints in solar cell production, contributing less to greenhouse gas emissions. On the other hand, advances in recycling techniques and strict waste management protocols have improved the sustainability of CdTe technology. Efforts to manage and recycle materials used in CdTe solar cells effectively reduce environmental risks and enhance their green credentials.

How Efficient are Cadmium Telluride Solar Cells?

The efficiency of Cadmium Telluride (CdTe) solar cells ranges from 8% to 22%, although their average efficiency is around 18%. The efficiency of CdTe solar cells is crucial as it directly impacts the energy conversion rate: how effectively sunlight can be converted into electrical energy. Higher efficiency rates mean more electricity can be generated from the same amount of sunlight, leading to more cost-effective and space-efficient solar energy systems.

The 8% lower threshold is generally associated with less optimized cells, earlier stages of technology development, or cells that are produced with less stringent quality control measures. The maximum efficiency recorded for laboratory CdTe solar cells has reached 22.1%, as achieved by First Solar. This represents the pinnacle of current CdTe technology under controlled conditions, demonstrating the potential of CdTe materials when optimized for peak performance.

Furthermore, First Solar, a leading manufacturer in the CdTe solar panel industry, reported that its average commercial module efficiency was approximately 18% at the end of 2020. This figure is notably high for commercial products and indicates that high-efficiency CdTe solar cells are not just theoretical but are being produced and used at scale. This level of efficiency in commercial modules is significant because it brings closer the gap between laboratory efficiencies and real-world application, highlighting improvements in manufacturing processes, material quality, and cell design.

How much is the Average price of Cadmium Telluride Solar Cells?

Solar panels made from Cadmium Telluride solar cells cost about $0.46 per watt, which is approximately 70% cheaper than crystalline panels, which range from $0.70 to $1.50 per watt. The lower cost of CdTe panels is largely due to the simpler and less expensive manufacturing process. Unlike silicon-based panels that require high-purity silicon and energy-intensive production methods, CdTe panels utilize a thin-film technology that requires less material and less energy to manufacture. Additionally, cadmium and tellurium, the primary materials used in CdTe panels, are by-products of mining operations, further reducing material costs.

Are Cadmium Telluride Solar Cells effective for high solar energy production?

Yes, Cadmium Telluride (CdTe) solar cells are effective for high solar energy production due to their significant light absorptivity and optimal bandgap, which enable high efficiency and low manufacturing costs. Although they are not the most efficient compared to some silicon-based cells, CdTe cells remain competitive due to their lower production costs, reduced material usage, and simpler manufacturing processes. These factors make CdTe solar cells a viable option for large-scale solar energy applications, offering a balanced solution between performance and cost-effectiveness. Despite their lower maximum efficiency, the economic and practical advantages they offer keep them at the forefront of renewable energy solutions.

Is Cadmium Telluride Solar Cell Better than Amorphous Silicon?

Yes, Cadmium Telluride (CdTe) solar cells are more efficient than amorphous silicon panels. CdTe stands out due to its higher efficiency in converting sunlight to electricity compared to amorphous silicon panels. The primary reason for the higher efficiency of CdTe lies in its material properties. CdTe has a direct bandgap that is well-suited to the solar spectrum, enabling it to absorb sunlight more effectively and convert it into electrical energy more efficiently. This direct bandgap allows CdTe cells to produce a higher amount of electrical current from the same amount of sunlight. In contrast, amorphous silicon has an indirect bandgap and typically exhibits lower light absorption and conversion efficiency.

Is Cadmium Telluride Solar Cell Better than Copper indium gallium selenide?

No, Cadmium Telluride (CdTe) is generally considered inferior to Copper Indium Gallium Selenide (CIGS), particularly due to the lower efficiency and higher production costs of CdTe cells.

In terms of efficiency, CIGS solar cells have achieved laboratory efficiencies of up to 22.8%, which is comparable to traditional crystalline silicon (c-Si) cells and higher than typical CdTe efficiencies. In comparison, the maximum efficiency recorded for laboratory CdTe solar cells has reached 22.1%, as achieved by First Solar. When it comes to costs, Copper Indium Gallium Selenide cells are produced with a cost expectation of $0.34/Watt for large-scale production, while Cadmium Telluride solar cells cost about $0.46 per watt. These factors contribute to the preference for CIGS over CdTe in solar power applications.