What is cadmium telluride?

Cadmium telluride overview

Cadmium telluride (CdTe) is an important group ⅱ-ⅵ compound semiconductor material with black crystalline particles or powders, melting point of 1092℃, relative molecular weight of 240, crystal structure of sphalerite type, with direct transition type band structure.  The lattice constant is 0.6481nm, the bandgap width is 1.45eV, the electron mobility at room temperature is 1050 C ㎡/(Vs), and the hole mobility at room temperature is 80 C ㎡/(Vs).  The bond energy of cadmium telluride is as high as 5.7eV, which is one of the most stable complexes of cadmium in nature.  Therefore, cadmium telluride is chemically stable at room temperature and insoluble in water and weak acids, so it is relatively safe in industrial production and use.  

It is worth mentioning that the spectral response of CDTE solar cells matches the spectral distribution of ground solar cells very well, and the actual power generation capacity is strong.

Cadmium telluride has stable properties and high light energy absorption coefficient. N-type or P-type semiconductor materials can be obtained by mixing different impurities, which can be used in the manufacture of nuclear radiation detectors (for medical purposes), infrared electro-optical modulators, infrared detectors, infrared lenses and Windows.  In the photovoltaic field, cadmium telluride is regarded as a key raw material for the preparation of large scale solar thin film cells.  Only 2μm (micron) thickness of cadmium telluride film, under the standard AM1.5 conditions, optical absorption rate of more than 90%, the highest theoretical conversion efficiency of 33%, so solar energy has become the largest application of cadmium telluride.  Cadmium telluride (5N) is typically used in the photovoltaic industry.  

Compared with other solar cells, the structure of CDTE thin film solar cells is simple.  Generally speaking, the traditional structure consists of five layers, namely glass substrate, transparent conductive oxide layer (TCO layer), cadmium sulfide (CdS) window layer, cadmium telluride (CdTe) absorption layer, back contact layer and back electrode.

Photovoltaic modules is the core part of photovoltaic power generation system, thin-film batteries has been developed including cadmium telluride (CdTe), copper indium gallium selenide (CIGS), gallium arsenide (GaAs), amorphous silicon thin film, organic thin film, a variety of technical route, such as perovskite cadmium telluride is now the city of the highest rates film component types, accounting for more than 95% of membrane components.  

CdTE thin film solar cells characteristics

1. The band gap width of cadmium telluride is 1.45eV, which is the absorption layer material of solar cells that best matches the ground solar spectrum;  

2. Cadmium telluride is a direct bandgap material with a high absorption coefficient of > 105/cm, 100 times that of silicon;  

3. Low temperature coefficient: the gap width of cadmium telluride is higher than that of crystal silicon, and the temperature coefficient is about half of that of crystal silicon. The temperature of components can exceed 65℃ in summer, and the power loss caused by temperature rise of cadmium telluride components is about 10% less than that of crystal silicon components.  

4. Small hot spot effect: cadmium telluride film components are long strip battery design, reduce the hot spot effect, improve the power generation capacity at the same time, improve product life and safety;  

5. Uniform color, beautiful and generous: large area cadmium telluride photovoltaic module uniform color, beautiful, strong sense of integration, especially suitable for high aesthetic requirements of buildings;  

6. High power generation efficiency: the theoretical limit conversion efficiency of cadmium telluride battery 32%-33%;  At present, the photoelectric conversion efficiency of small-area cells is 22.1% in the world, and the component efficiency is 19%, and there is still a large room for improvement.  

7. High degree of customization:  With unique production technology, Longyan has developed 8 categories such as electric wall, power generation tile and power generation brick, and more than 50 kinds of CDTE thin film photovoltaic building materials suitable for different building application scenarios. It can flexibly customize color, pattern, shape, size and transmittance according to different needs.  Gradually realize the grand goal of replacing traditional building materials with photovoltaic building materials in building applications.

Compared for silicon components, cadmium telluride thin-film module has high absorption coefficient, hot spot effect small, weak light effect is good, beautiful degree is high, the characteristics of customizability, flexible application can be used for building on the roof, wall and other architectural structure, and make the best use of the surface of the building the increasing effective area, meet the requirements of multi-angle power, finally from the source to reduce carbon emissions.  Driven by favorable policies, the demand for CDTE thin film photovoltaic modules will further expand in the future.