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Amorphous silicon technology and it's advantages

Amorphous silicon is form of silicon, the second most abundantly occurring natural element on Earth. However, it differs from silicon in that it is non-crystallized and disordered in the same way that ordinary glass is, meaning that some of the atoms in its chemical structure resist bonding. These so-called “dangling” bonds impact the inherent properties of the material, namely giving it a higher defect density, which refers to the amount of naturally occurring imperfections. This substance, often abbreviated to a-Si, still offers several advantages over crystalline silicon that makes it preferable for use in manufacturing thin films for coating a variety of electronic components, particularly photovoltaic (PV) systems. For instance, it can be applied to large areas in a more homogeneous manner than silicon and at very low temperatures, allowing it to adhere to glass, plastic, and metals. Before amorphous silicon can be applied as a thin film to certain materials, such as solar cells, it has to go through hydrogenation to lend the material greater stability and durability. This means that the dangling bonds must undergo “passivation,” a process in which the unordered bonds in each layer of silicon cells are saturated with atomic hydrogen while under pressure between layers of transparent conductor and a metal backing, usually tin oxide and aluminum, respectively. This modification allows for greater flexibility in terms of how the material may be deposited, as well as offering more control over its voltage properties. As a result, amorphous silicon can be used in thin film processes employed to make a variety of low-voltage devices, such as pocket calculators and watches. Another advantage of utilizing amorphous silicon thin film over crystalline silicon is that the former absorbs up to 40 times more solar radiation. That being the case, only a very thin film coating is necessary to absorb 90 percent or more of direct sunlight. In fact, the coating only has to be 0000 039 37 inch, or one micrometer in thickness. To put this into perspective, a single strand of human hair has a thickness 100 times greater. This attribute adds to the cost effectiveness of using amorphous silicon in thin film technologies.

Thin film silicon, is expected to achieve large-scale production among various types of thin-film solar cells. CdTe and CIS, CIS thin film solar cell manufacturing process need massive metals of selenium, making production costs very high, and CIS production is complex, mass production has caused some difficulties, so the time was not yet fully mature. As for the CdTe thin film solar cell, due to its raw material in the "CD" proved to be a carcinogen, so green energy with solar panels feature a slight conflict, in addition to its raw material in the "te", the price is more expensive. In contrast, thin film silicon solar cells are more suitable for large scale production.

 

Amorphous silicon properties
When the output power of solar cells reach up to the best work temperature 25 °, then temperature will decrease as temperature rises. Especially in the hot summer months, at high temperatures, power will be much greater. Compared to crystalline silicon solar cells, amorphous silicon thin film solar cells have good low temperature properties and therefore more suitable to work under conditions of high temperature in the summer. Amorphous silicon thin-film cells can produce more electricity when compare to other type of solar cells with the same power output.  It is because Amorphous silicon thin film solar cells have the following characteristics:

 

Low-temperature characteristics and advantages
Generally speaking, PV module performance parameters are measured under standard test conditions, and standard test conditions (STC): (light intensity: 1000W/M2; frequency: 1.5 amp; component temperature: 25 c). When PV components are working outdoors, its temperature is higher than 25 degrees centigrade, and components that are installed on the roof, the working temperature is higher, practical component operating temperatures often reached 55 degrees or above. Consumers, therefore, when you select the type of PV module, temperature coefficients should be used as one of the more important factors to consider. Because as the temperature rises, the component's output power is reduced accordingly. Amorphous silicon thin film solar cell temperature coefficients for -0.2%/℃, and the temperature coefficient of crystalline silicon is-0.5% degrees centigrade.

This means that when the temperature of a component reaches 50 degrees Celsius, it will reduce the power compared to 25 c under standard conditions is about 5%, and crystalline silicon power attenuation is about 12.5%. Therefore, even under standard test conditions of amorphous silicon thin film solar cell conversion efficiency is lower than that of crystalline silicon cells, but in practice, average productivity of difference between them would be reduced.

 

Efficient under poor light performance:
Amorphous silicon thin film solar cells under weak light conditions work much better than the crystalline silicon, in practical applications, PV modules in 1000W/M2 works under the standard light intensity is very rare, very often the light intensity are below this intensity and crystalline silicon cells in order to achieve the ideal working conditions, require bright light exposure vertically.  Amorphous silicon thin film solar cell to light intensity and sun angle constraints are much smaller, so over a period of time before Sun, crystalline silicon cells might not be able to continue to make electricity, but thin-film  battery can continue to work. Another point, amorphous silicon thin film solar cells have a more mild form of I-v curves, so it can work faster to achieve the best output.

 

No need to be angled to collect better solar energy.
Crystalline Silicon need to be angled at 45 c in order to collect a signifcant amount of solar energy,  a-Si modules can collect very good amount of solar energy at any angle.

 

Heat Resistance
Crystalline solar panels suffer a reduction in output once the temperature from the sunlight reaches a higher degree, but thin film a-Si solar photovoltaic glass has no limit, it can generate the electricity depends on the brightness of the sun.


The difference between Thin film a-Si and crystalline solar panel



 


Test to prove that thin film a-Si solar panel can generate a lot more than crystalline Solar panel

 

Thin film a-Si Panel 12W and Crystalline Solar panel 12W Test Result
A
1. Test Conditions: Test Sample, Solar-Motion thin film panels 12w and Crystalline Solar panel 12w.
2. Test Equipments: Irradiance meter, 
3. Four channel micro voltage acquisition system
4. Two Lead acid storage with the same specifications of 12V/12Ah.
5. Test area: HangZhou (East longitude; 119°, north longitude 30°) outdoor, no shelters; PV module face south with slop 30°


                  Crystalline Solar Panel         Thin Film a-Si Solar Panel

 
Two Lead acid storage with the same specifications of 12V/12Ah.

 

Photo #2: The comparison of thin film a-Si panels and crystalline soar panel under cloudy day

B. Test Result; Data collected total 4 days, first two days are cloudy and raining for the daytime, the after two days are normal good sunlight for the daytime.

 

 


From photo#2 and #3, you can see no matter cloudy & ranining day or normal day. Under the same irradiance, thin film a-Si pv module can generate a lot more power than crystalline solar panel. 

The comparison of charge quantity between thin film a-Si panels and crystalline soar panel.

From Photo#4, you can see that after 4 days, thin film a-Si panel can generate a lot more power than crystalline solar panel. The charge quantity crystalline solar panel is 4.68Ah, and the charge quantity of thin film a-Si panel is 6.10Ah

Conclusion: Under the conditions of the same irradiance, output power and charge time, thin film a-Si panel charge quantity is 1.35 times of crystalline solar panel. At cloudless day, the charge quantity of thin film a-Si panel is 1.30 times of crystalline solar panel.

Note:The difference of irradiance between Cloudy and cloudless. See the follow photos