What is Solar Cell Energy?

A solar cell is also called a " solar chip " or " photocell" , which is a type of photovoltaic semiconductor sheet that directly generates electricity using sunlight. As long as it is illuminated by a certain illuminance condition, it can output voltage instantly and generate current in the presence of a loop. Physically called solar photovoltaic (Photovoltaic, abbreviated as PV ), referred to as photovoltaic .

Data show that in 2012, China's solar cells continued to maintain output and cost-effectiveness advantages, and their international competitiveness was increasingly strengthened.

With the continuous development of the solar cell industry, internal competition is also intensifying, mergers and acquisitions and capital operations between large solar cell companies are becoming more frequent, and excellent domestic solar cell manufacturers are paying more and more attention to the research of the industry market, especially for the In-depth research on the industrial development environment and product buyers. Because of this, a large number of outstanding domestic solar cell brands have risen rapidly and gradually become the leader in the solar cell industry ^[1]

The term "Photovoltaics" comes from Greek and means

The sun shines on the semiconductor

The composition of solar cell modules and the functions of each part

1)

The basic characteristics of solar cells are the three basic characteristics of the polarity of the solar cell, the performance parameters of the solar cell, and the volt-ampere characteristics of the solar energy environmental protection battery. The specific explanation is as follows

1.Polarity of solar cell

Silicon solar cells are generally made of P + / N-type structure or N + / P-type structure, P + and N +, which indicate the conductivity type of the semiconductor material on the front light-emitting layer of the solar cell; N and P, which indicate the conductivity type of the semiconductor material on the back substrate of the solar cell . The electrical properties of solar cells are related to the characteristics of the semiconductor materials used to make the cells.

2. Performance parameters of solar cells

The performance parameters of solar cells are composed of open circuit voltage, short-circuit current, maximum output power, fill factor, and conversion efficiency. These parameters are indicators of the performance of solar cells.

3 Volt-ampere characteristics of solar cells

The PN junction solar cell includes a shallow PN junction formed on the surface, a strip-shaped and finger-shaped front ohmic contact, a back ohmic contact covering the entire back surface, and an anti-reflection layer on the front. When the battery is exposed to the solar spectrum, photons with energy less than the forbidden band width Eg do not contribute to the battery output. Photons with energy greater than the forbidden band width Eg will contribute energy Eg to the battery output, and energy less than Eg will be consumed in the form of heat. Therefore, in the design and manufacture of solar cells, the influence of this part of heat on the stability and life of the battery must be considered.

1.Open circuit voltage

Open-circuit voltage UOC: Put the solar cell under AM1.5 spectral conditions and 100 mW / cm2 light source intensity. When the two ends are open, the output voltage of the solar cell.

2. Short-circuit current

Short-circuit current ISC: It is the value of the current flowing through the two ends of the solar cell when the solar cell is placed under the AM1.5 spectral condition and the light source intensity of 100 mW / cm2 is irradiated.

3.Maximum output power

The working voltage and current of a solar cell change with the load resistance. The working voltage and current values corresponding to different resistance values are made into a curve to obtain the volt-ampere characteristic curve of the solar cell. If the selected load resistance value can maximize the product of the output voltage and current, the maximum output power can be obtained, which is represented by the symbol Pm. The operating voltage and operating current at this time are referred to as the optimal operating voltage and the optimal operating current, and are represented by the symbols Um and Im, respectively.

4.

The solar AC power generation system is composed of a solar panel, a charging controller, an inverter, and a battery; the solar DC power generation system does not include an inverter. In order for the solar power generation system to provide sufficient power for the load, it is necessary to reasonably select each component according to the power of the consumer. The following uses the output power of 100W for 6 hours per day as an example to introduce the calculation method:
1. First, calculate the number of watt hours consumed per day (including the loss of the inverter):

If the inverter conversion efficiency is 90%, when the output power is 100W, the actual output power should be 100W / 90% 111W; if it is used for 5 hours per day, the power consumption is 111W × 5h = 555Wh .

1. Calculate solar panels:

Calculated based on the effective daily sunshine time of 6 hours, and taking into account the charging efficiency and losses in the charging process, the output power of the solar panel should be 555Wh / 6h / 70% = 130W. 70% of this is the actual power used by the solar panel during the charging process.

Solar cells are mainly based on semiconductor materials. Their working principle is to use photoelectric materials to absorb photoelectric energy and convert them into photoelectric conversion reactions. Depending on the materials used, solar cells can be divided into: 1. silicon solar cells; 2. inorganic salts Such as gallium arsenide III-V compounds, cadmium sulfide, copper indium selenium and other multi-component batteries as materials; 3, solar cells made of functional polymer materials; 4, nanocrystalline solar cells.

According to the crystalline state, solar cells can be divided into two types: crystalline thin-film type and amorphous thin-film type (hereinafter referred to as a-), and the former is divided into single crystalline form and polycrystalline form.

According to the material, it can be divided into silicon thin film,

Monocrystalline silicon solar energy has the highest photoelectric conversion efficiency of 24%, which is the highest among all types of solar cells. However, the production cost of single crystal silicon solar cells is so great that it cannot be widely and widely used. In terms of production cost, polycrystalline silicon solar cells are cheaper than monocrystalline silicon solar cells, but the photoelectric conversion efficiency of polycrystalline silicon solar cells is reduced a lot. In addition, the service life of polycrystalline silicon solar cells is shorter than that of monocrystalline silicon solar cells. . Therefore, in terms of cost performance, single crystal silicon solar cells are still slightly better.

Researchers have found that some compound semiconductor materials are suitable for solar photovoltaic conversion films. For example, CdS, CdTe; III-V compound semiconductors: GaAs, AIPInP, etc .; thin-film solar cells made with these semiconductors show good photoelectric conversion efficiency. Semiconductor materials with multiple gradient band gaps (the difference in energy levels between the conduction band and the valence band) can expand the range of the solar absorption spectrum, thereby improving the photoelectric conversion efficiency. So that a large number of practical applications of thin-film solar cells present broad prospects. Among these multiple semiconductor materials, Cu (In, Ga) Se2 is an excellent solar light absorbing material. Based on it, a thin-film solar cell with a photoelectric conversion efficiency significantly higher than that of a silicon thin-film solar cell can be designed, and the photoelectric conversion rate that can be achieved is 18% ^[1]

Here is just a brief introduction to the role of technology, to give everyone a perceptual understanding.

The US Department of Commerce has raised anti-subsidy tariffs on Chinese solar cell products exported to the United States, but maintained or reduced anti-dumping tariffs on such products. The case has exacerbated trade tensions between China and the United States.

The case also caused divisions in the U.S. solar industry (one camp was a company with large-scale manufacturing operations in the U.S. and the other was a company that relied on Chinese exports to the United States) and triggered retaliation in Beijing.

The U.S. Department of Commerce said on Wednesday that it will impose a countervailing duty of 14.78% to 15.97% (depending on the specific manufacturing company) on imported solar cell products, significantly higher than its preliminary ruling of 2.9% to 4.73% announced in March. However, the US Department of Commerce also decided to maintain or reduce its anti-dumping tariffs announced in May (for imported products that the US considers to be unfairly priced low).

Jigar Shah, chairman of Campaign for Affordable Solar Energy, an alliance of companies that buy Chinese solar cells, said: "We are pleased to see that the Ministry of Commerce has not substantially Raise tariffs. "

But the case, the first US anti-dumping action in the renewable energy industry, is still a source of tension between the US and China. China has announced an anti-dumping investigation on polysilicon imported from the United States as a solar cell raw material, a move apparently intended to retaliate.

The case also highlights the U.S.'s controversial practice of imposing countervailing and antidumping duties on the same type of imports from so-called "non-market economies" such as China and Vietnam; after 23 years of suspension, George W. Bush ( (George W. Bush) The government restarted this policy in 2007. A federal court in the United States has declared this practice illegal, but the US Congress later passed relevant legislation that overturned the court's ruling.

In September, the same day that U.S. President Barack Obama announced a lawsuit against China at the World Trade Organization (WTO), accusing China of providing illegal export subsidies to the auto parts industry, China filed a lawsuit against the WTO. Litigation of the above-mentioned new law in the United States.

A group of companies led by Germany-based SolarWorld, which has led the U.S. business to urge the import tariffs, has called on the EU to impose similar tariffs on Chinese solar products. But the outlook for the EU case changed in August because German Chancellor Angela Merkel said during her visit to China that month that she would prefer a negotiated solution ^[2]

There are many kinds of materials for solar cells. There can be semiconductors such as amorphous silicon, polysilicon, CdTe, CuInxGa (1-x) Se2, or materials linked to the elements of Groups 3, 5 and 26. Simply put, where After the light is generated, it is the material that the solar cell seeks.

The electric vehicle solar charging station mainly uses different processes and methods to test the reaction and absorption of light, to achieve a revolutionary breakthrough in the combination of wide energy gaps and short-wavelength or long-wavelength absorption that can reduce the cost of materials. .

There are also different types of solar cells. The substrate type or the thin film type. The substrate can be divided into single crystal type in the manufacturing process, or it can be mixed and cooled to form a polycrystalline block. The thin film type can be better with buildings. In combination, if there is curvature or flexible, folding type, amorphous silicon is more commonly used in materials. There is also an organic or nano material research and development, which is still a forward-looking research and development. Therefore, that is to hear different generations of solar cells: the first generation of substrate-based silicon (Silicon Based), the second generation of thin film (Thin Film), the third generation of New Concept (New Concept), the fourth generation of composite film materials.

The first generation of solar cells has the longest-developed technology and the most mature technology. It can be divided into: Monocrystalline Silicon, Polycrystalline Silicon, and Amorphous Silicon. In terms of applications, the former two monocrystalline silicon and polycrystalline silicon are the bulk.

The second-generation thin-film solar cells use a thin-film process to make the cells. Types can be divided into Cadmium Telluride CdTe, Copper Indium Selenide (CIS), Copper Indium Gallium Selenide (CIGS), Gallium arsenide GaAs

The biggest difference between the third generation battery and the previous generation battery is the introduction of organic matter and nanotechnology in the process. Types include photochemical solar cells, dye photosensitized solar cells, polymer solar cells, and nanocrystalline solar cells.

The fourth generation is a multilayer structure for thin films that absorb light from batteries.

Some kind of battery manufacturing technology. It is not possible to manufacture only one type of battery. For example, in the polysilicon process, both the silicon wafer type and the thin film type can be manufactured.

Solar cell polymer solar cell material

Common materials for polymer solar cells are polyvinyl carbazole (PVK), polyacetylene (PA), polyparaphenylene vinylene (PPV), and polythiophene (PTh).

(1) Polyvinyl carbazole (PVK)

Among the polymers with optoelectronic activity, the earliest and most thoroughly studied is PVK, which has a large electron conjugated system on its side groups and can absorb ultraviolet light. The excited electrons can freely migrate through the charge complex formed by adjacent carbazole rings. It is usually doped with I2, SbCl3, trinitrofluorenone (TNF), and nitrostilbene benzene derivative tetracyanoquinone (TCNQ).

(2) Polyacetylene (PA)

PA is the electronic polymer with the highest measured conductivity to date. Its polymerization methods include Shirakawa Hideki method, Namm method, Durham method and rare earth catalyst system. Hideki Shirakawa uses a high-concentration Ziegler-Natta catalyst, namely TiOBu4-A1Et3, starting from gas-phase acetylene to directly prepare a self-supporting polyacetylene film with metallic luster; it is formed on an aligned liquid crystal substrate, and the PA film is also highly oriented . The Narrman method is characterized by "high temperature aging" of the polymerization catalyst, so the mechanical properties and stability of the polymer are significantly improved.

(3) Poly-p-phenylene vinylene (PPV)

In recent years, the most widely used in the field of optoelectronics, the most efficient device is PPV materials. Due to the conjugate structure, the molecular chain is very steel, which is often refractory and insoluble and difficult to process. The method of obtaining soluble PPV is to introduce at least one long-chain alkane on the benzene ring. The number of alkane carbons is at least greater than 6. The study also found that when the substituents are branched, they have better solubility than straight-chain alkanes of the same carbon number. A representative material is MEH-PPV (MEH; 2-methoxy-5 (2'-ethylhexyloxy)), which has good solubility and is easy to use; the band gap is 2.1eV, which is moderate.

(4) Polythiophene (PT) derivatives

Among all the conjugated polymers, polythiophene is a very good photovoltaic material. Because of its suitable band gap and high hole mobility, it has become one of the research hotspots for organic photovoltaic materials. Among them, a photovoltaic device using a regionally-structured poly (3-hexyl) thiophene (P3HT) and a soluble C60 derivative PCBM as the active layer has the highest energy conversion efficiency under heat treatment, and the energy conversion efficiency has reached 5 %about. Therefore, a new type of polythiophene derivative was designed and synthesized, and the relationship between the structure and properties of polythiophene was studied. The structural modification to improve the properties of polythiophene derivatives has attracted the attention of researchers. From the perspective of photovoltaic materials, these polythiophene derivatives should have the most basic properties: good solubility and film-forming properties, a broad absorption spectrum (especially in the visible light region) and higher carrier mobility ^{[1 ]} .