The Cadmium Telluride (CdTe) solar technology was first introduced in 1972 when Bonnet and Rabenhorst designed the CdS/CdTe heterojunction that allowed the manufacturing of CdTe solar cells. At first, CdTe panels achieved a 6% efficiency, but the efficiency has tripled to this day.
Companies like Kodak, Monosolar, AMETEK, and many others have researched CdTe technology. Nowadays, CdTe technology is the most popular thin-film solar panel technology and it is the preferred option by the top 10 manufacturers of thin-film solar panels in the world.
In this article, we will do a deep dive on CdTe solar panels and everything related to this technology. We will explain the materials and manufacturing process for these thin-film solar panels, possible applications, and compare them to other technologies.
What is a Cadmium Telluride (CdTe) solar panel?
Cadmium Telluride solar panels are the most popular thin-film solar panels available in the market. These represent around 5% of the solar panels in the world market and come only second to crystalline silicon panels.
CdTe thin-film solar panels are so popular because they are easy and not expensive to manufacture, making them ideal for investors. CdTe panels have an average efficiency of 19%, but laboratory tests performed by First Solar, have achieved record efficiencies of 22.1% for CdTe solar cells.
Understanding CdTe thin-film solar panels, is vital to know the true advantages and possible applications for these thin-film solar panels. In this section, we will explain the materials, manufacturing process, and other interesting details about CdTe solar panels.
Materials used in CdTe thin-film solar cells and panels
CdTe cells are made by using semiconductors that optimize the efficiency of transforming solar radiation into electricity. CdTe solar cells are made by using p–n heterojunctions containing a p-doped Cadmium Telluride layer and an n-doped Cadmium Sulfide (CdS) layer, which may also be made out of magnesium zinc oxide (MZO).
While these materials are cheap, they can also be toxic and pollutant when improperly disposed of. Greenpeace has warned about the toxicity and contamination levels of these materials, stating that CdTe panels contain 6g/m2 of toxic metals and they produce cadmium emissions equivalent to 0.5g/GWh. There are also several health concerns attached to these materials.
Aside from materials used for CdTe cells, there are other materials required to make CdTe thin-film solar panels. These materials are:
- Fluorine-doped tin oxide (SnO2:F)
- Zinc telluride (ZnTe)
- Copper (Cu)
The manufacturing process of CdTe thin-film solar panels
CdTe thin-film solar panels are comprised of three main parts, having a layer for the semiconductor, one for the protection, and one for the conduction. These parts are:
- Photovoltaic material
- Conductive sheet
- Protective layer
Each of these sections is vital for CdTe thin-film solar panels. The manufacturing process is made through a different set of methods called deposition techniques. The different types of techniques used are sputtering, chemical spray pyrolysis, electrodeposition, or close vapor transport (CVT). The materials used in each of these parts of the CdTe thin-film solar panels are the following:
The photovoltaic material is the part of the CdTe thin-film solar panel that converts solar radiation into DC energy. This is manufactured by creating a p–n heterojunction, this semiconductor requires the deposition of a layer of CdTe for the p-doped section and one of CdS or MZO for the n-doped section.
The conductive sheet allows the DC energy to flow between solar cells, increasing the voltage and allowing for the connection of CdTe panels into photovoltaic (PV) systems. These layers require the deposition of a metal layer or carbon paste, introducing copper (Cu) to create conduction in the panel.
Photovoltaic layers tend to be very fragile, which is why thin-film solar panels require a protective layer. Instead of using an aluminum frame and tempered glass, this layer known as the Transparent Conductive Oxide (TCO) layer, is made by depositing SnO2:F or a similar material. The TCO layer is where the CdTe absorber is deposited, allowing the solar cell to be fully protected.
CdTe solar panels vs. Other types of thin-film panels
CdTe solar panels are not the only thin-film panels in the market. Aside from these, there are three main options available:
- Amorphous silicon (a-Si) solar panels
- Copper indium gallium selenide (CIGS) solar panels
- Gallium arsenide (GaAs) solar panels
These thin-film solar panels and CdTe have many differences. For a better understanding of these, we will compare each thin-film solar panel against CdTe panels, considering materials, efficiency, application, and other aspects.
Amorphous silicon (a-Si) vs. CdTe solar panels
A-Si thin-film solar panels are less efficient than CdTe panels, achieving a 6-7% efficiency. Since a-Si solar panels are cheaper and less toxic than other options, they have become the second most popular option for thin-film solar panels.
The a-Si solar panels are regularly used in small-scale applications. Recent developments show promising results for these panels in the future since they have the potential to be integrated into clothing.
Producing a-Si solar panels is cheaper and easier than CdTe panels because they only require a fraction of the silicon that other panels do. These are manufactured through an evaporation method, allowing for the fabrication of a thin semiconductor layer that is placed on glass or stainless steel.
Copper indium gallium selenide (CIGS) vs. CdTe solar panels
CIGS solar panels are less toxic than CdTe, but they still represent moderate toxicity for respiratory tracks in humans. These thin-film solar panels are less efficient than CdTe, achieving a 12-14% efficiency, but laboratory studies have recorded excellent efficiency results of 20.4%.
While production costs for CIGS thin-film solar panels are not as cheap as CdTe, new manufacturing processes with lower costs are being developed. These panels are usually manufactured through sputtering, evaporation, electrochemical depositions, and several other processes.
CIGS thin-film solar panels are usually used in facades and windows since they are very easy to install and have a pretty decent efficiency. These thin-film solar panels are considered for space applications.
Gallium arsenide (GaAs) vs. CdTe solar panels
GaAs thin-film solar panels can achieve an efficiency of 28.8%, making them the most efficient and durable thin-film solar panels available, but they are also the most expensive. GaAs is slightly less toxic than CdTe, but it is still the second most toxic semiconductor in the list.
The manufacturing process for GaAs is more expensive and complex than CdTe. These panels require a growing process on a doped substrate, afterwards, they are coated with anti-reflecting and metallization materials. In the future GaAs thin-film, solar panels could end up costing much less.
GaAs solar panels are rarely sold in the market. These thin-film panels are more frequently used for spacecraft, military vehicles, space missions, and other specialized applications.
CdTe solar panels vs. Crystalline silicon solar panels (Pros and cons)
CdTe solar panels and crystalline silicon solar panels are very different technologies. To know which one is the best technology, we will compare them, highlighting and considering the pros and cons of each one for analysis.
|Crystalline Silicon Solar Panels||CdTe Solar Panels|
|Type of Technology||Cadmium Telluride (CdTe)|
|Temperature Coefficient||-0.446%/ºC to -0.387%/ºC||-0.172%/ºC|
|Compatibility With Inverters||Most inverters in the market are designed for the low-temperature coefficient of these panels||Installers have to consider temperatures at the installation place concerning temperature coefficient|
|Required Space||Standard requirements||Require up to 31% more space per kW installed|
One main advantage of CdTe technology is the low cost of manufacturing. CdTe panels can be found at low prices of $0.46/Watt, which is 70% cheaper than the cost for crystalline panels. Another strong advantage of CdTe technology is that it is less affected by strong changes in temperatures, delivering a constantly higher voltage in PV systems.
While crystalline solar panels are more efficient than CdTe (making them better for residential markets), this does not mean that they are more suitable for all types of installations. In some industrial applications in hot weather, solar farms with CdTe panels can have the potential of delivering a higher power output than crystalline silicon solar panels.
CdTe panel application: When to use CdTe solar panels?
Even though CdTe panels are not always the best option for residential applications, these panels are quite versatile for commercial and industrial applications.
CdTe solar panels are 1-6% less efficient than crystalline modules, but they have prices 70% lower. These low prices make CdTe an excellent technology for solar farm installations where space is not a problem. These solar farms could deliver cheaper electricity than fossil fuel power and even crystalline silicon solar farms.
Since CdTe thin-film solar panels are more adaptable to different structures, they can be installed in different aircraft and be used for space applications. Unmanned aerial vehicles with this technology in space, can be highly benefited from CdTe panels since they are cheap, shape-adaptable, and very lightweight.
CdTe thin-film technology is very promising. These panels are excellent for industrial and commercial applications, and they could even be installed in the future at the roof of electric vehicles (EVs) since they can be easily installed at odd structures like the hood or roof of a car.
There should not be any doubts regarding the popularity of CdTe technology as the best thin-film solar panel. These modules are cheap, lightweight, resistant, have high efficiency, and are easy to manufacture, making them excellent for a wide variety of applications.
While CdTe solar panels are still not widely used in residential applications, they are still used in the commercial and industrial sectors.
The future of CdTe thin-film solar panels is very promising. These panels are the preferred option for space aircraft, some solar farms, and we could even see them on the roofs of EVs in the future.