There are many applications of solar cells in life, such as the solar panels in the bicycle basket of meituan. In previous articles on solar cells, the thin film solar cells are introduced. In order to enhance our understanding of thin-film solar cells, this paper will introduce the advantages and disadvantages of thin-film solar cells and the production of thin-film solar cells. If you are interested in solar cells, read on.
1、 Advantages and disadvantages of thin film solar cells
The first mock exam of thin film solar cells is that the cost of each module is much less than that of the stacked solar cells because of the less materials used. The energy required for the manufacturing process is smaller than that of the stacked solar cells. It also has integrated modules, which saves the cost of fixed and internal connections for the independent modules. In the future, thin film solar cells will replace the common silicon solar cells and become the mainstream of the market. The main difference between amorphous silicon solar cells and monocrystalline silicon solar cells or polycrystalline silicon solar cells is the material. The material of monocrystalline silicon solar cells or polycrystalline silicon solar cells is sparse, while the material of amorphous silicon solar cells is SiH4. Because of the different materials, the structure of amorphous silicon solar cells is slightly different from that of crystalline silicon solar cells.
The biggest advantage of SiH4 is that it has good light absorption effect and photoconductive effect, but its electrical characteristics are similar to insulator, which is far from the semiconductor characteristics of silicon, so SiH4 was initially considered as an unsuitable material. But in the 1970s, scientists overcame this problem, and soon RCA in the United States produced the first amorphous silicon solar cell. Although SiH4 has good light absorption and photoconductivity, its crystal structure is worse than that of polycrystalline silicon solar cells, so the problem of floating bonds is more serious than that of polycrystalline silicon solar cells, and the recombination rate of free electrons and holes is very fast; In addition, the irregular crystal structure of SiH4 will hinder the movement of electrons and holes and shorten the diffusion range. Based on the above two factors, when light irradiates SiH4 to produce electron hole pairs, it is necessary to separate the electron from the hole as soon as possible to effectively produce photoelectric effect. So most of the amorphous silicon solar cells are made very thin to reduce the recombination of free electrons and holes. Due to the good light absorption effect of SiH4, although the amorphous silicon solar cell is very thin, it can still absorb most of the light.
The structure of amorphous silicon thin film solar cell is different from that of ordinary silicon solar cell, as shown in Fig. 9. It can be mainly divided into three layers, the upper layer is very thin (about 0.008 μ m) and has high doping concentration of P +; The middle layer is a thicker (0.5 ∼ 1 μ m) pure layer, but generally speaking, the pure layer is not completely pure, but n-type material with low doping concentration; The lowest layer is the thinner (0.02 μ m) n. The P + – I-N structure has a larger electric field than the traditional p-n structure, which makes the electron hole pairs generated in the pure layer can be quickly separated by the electric field. The thin oxide film on P + is transparent conductive xide:TCO ）It can prevent sunlight reflection to effectively absorb sunlight, usually using silicon dioxide (SnO2). The biggest advantage of amorphous silicon solar cells is low cost, but the disadvantage is low efficiency and photoelectric conversion efficiency decline with time. Therefore, amorphous silicon solar cells are widely used in the small power market, but they are less competitive in the power generation market.
2、 How to produce thin film solar cells
Cost is the biggest obstacle to the widespread use of solar technology. Traditional silicon solar cells need complex and time-consuming production process, which greatly increases the cost of each kilowatt hour. Non silicon thin film solar cells are easy to produce, so it is easier to break through the cost barriers.
The biggest breakthrough in the production of thin film solar cells is in the chaff like copper indium gallium selenium cells. Nano solar companies use a method similar to offset printing to produce their solar cells. Let’s see how they do it. First of all, a large number of aluminum strips are slowly moving forward in the huge printer, just like printing newspaper, the aluminum strip roll can reach several meters wide and miles long, which makes the product can be used for different purposes. Next, a printer operating in the open air deposits a thin layer of semiconductor ink onto an aluminum substrate. This is a great progress made in the mass production of glassy copper indium gallium selenium battery and cadmium telluride battery. The original production requires semiconductor deposition in vacuum chamber, but now it can be carried out in the open air, with faster speed and lower cost. Next, another press deposits a thin layer of cadmium sulfide and zinc oxide, which is non reflective, ensuring that sunlight reaches the semiconductor layer. Finally, the aluminum foil is cut into pieces of solar cells. Similar to the traditional silicon solar cells, it is possible to assemble them by classification in the production process of nano solar companies, which means that the electrical characteristics of the cells can be satisfied, and the highest panel efficiency distribution and yield can be achieved. However, the glass state CuInGaSe battery does not provide self-assembled taxon, because the panel of the battery does not conform to the electrical characteristics well, and its energy yield and efficiency are greatly reduced.
Printers for semiconductor printing are easy to use and maintain. Not only that, but also the waste of raw materials is very small, which helps to improve the efficiency of the whole production process and reduce the cost of solar panel power generation. It costs three dollars to produce a watt of electricity from traditional solar panels. The traditional idea is that solar technology will not be competitive until the cost is reduced to one dollar per watt. Nano solar claims that its ultra efficient production and revolutionary semiconductor ink will reduce the cost of solar power to just 30 cents per watt. If that’s true, then solar can compete with coal.
Thin film solar technology is not science fiction. Nano solar products have a wide range of customers, including partners and government departments all over the world, and thin film solar cell producers are also very busy. The first solar energy agency in Ohio cooperated with Juwei solar energy agency to build a 40 MW CdTe thin film solar energy base in Saxony, Germany, which was completed in 2009. Honda is actively carrying out the test of integrated CuInGaSe thin film solar cells.
If solar thin film cells can bring their potential into full play, it is not difficult to imagine that in the near future, solar energy will be as ubiquitous as sunlight. In urban buildings, thin film solar cells will cover the roof and the front of the house. In new houses, they will be installed as a whole as roof cardboard. In addition, they can power a new generation of solar powered cars and trucks.