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Polycrystalline silicon solar cells
Battery released in 2004
Polycrystalline silicon solar cells combine the high conversion efficiency and long life of monocrystalline silicon cells as well
Amorphous silicon thin film battery
The material preparation process is relatively simplified and other advantages of the new generation of batteries, which
Conversion efficiency
It is generally about 17-18%, slightly lower
Single crystal silicon solar cell
There is no obvious efficiency decline problem, and it is possible to prepare on cheap substrate materials, the cost is much lower than monocrystalline silicon cells, and the efficiency is higher than amorphous silicon thin film cells.
- Chinese name
- Polycrystalline silicon solar cells
- Foreign name
- Multicrystalline silicon solar cell
- Production technology
- with Single crystal silicon solar cell Much the same
- Listing date
- July 1, 2004
- nature
- Solar cell
- domain
- electricity
Manufacturing process of polycrystalline silicon solar cell and
Single crystal silicon solar cell
Pretty much, but polysilicon solar cells
Photoelectric conversion efficiency
It is necessary to reduce a lot, and its photoelectric conversion efficiency is about 17-18%. Polycrystalline silicon wafer production low energy consumption, production process pollution-free, compared with monocrystalline silicon solar cells, polycrystalline
Silicon solar cells are more economical.
[1]
In terms of production cost, compared to
Single crystalline silicon solar cell
It is cheaper, the material is simple to manufacture, the power consumption is saved, and the total production cost is low, so it has been greatly developed. In addition, the service life of polycrystalline silicon solar cells is shorter than that of monocrystalline silicon solar cells.
Single crystal silicon
The production of solar cells requires the consumption of a large number of high-purity silicon materials, and the manufacturing process of these materials is complex, and the power consumption is large, and the total cost of solar cell production has exceeded half. In addition, the drawn monocrystalline silicon rod is cylindrical, and the sliced solar cell is also a round sheet, which makes the plane utilization rate of the solar module low. Therefore, since the 1980s, some countries in Europe and the United States have invested in the development of polysilicon solar cells. Due to the obvious grain interface and lattice dislocation in polysilicon, its efficiency is relatively low. In addition
Carrier mobility
, life and diffusion length, compared with monocrystalline silicon solar cells,
Polycrystalline silicon solar cells
They're all much lower.
[2]
1)
Tempered glass
Its role is to protect the main body of power generation (battery), the selection of light transmission is required, 1. Light transmittance must be high (generally more than 91%); 2. Super white tempering treatment
2) EVA is used for bonding and fixing tempering
glass
And the power generation body (battery), the quality of transparent EVA material directly affects the life of the component, exposed to the air
EVA
Easy to age yellow, thus affecting the transmittal rate of the component, thus affecting the power generation quality of the component in addition to the quality of EVA itself, the impact of the lamination process of the component manufacturer is also very large, such as EVA adhesive connection is not up to standard, EVA and tempered glass, backplane bonding strength is not enough, will cause early aging of EVA, affecting the life of the component.
3) The main role of the battery is to generate electricity, the mainstream of the main power generation market is crystalline silicon solar cells, thin film solar cells, both have advantages and disadvantages of crystalline silicon solar cells, the equipment cost is relatively low, but the consumption and the cost of the battery is high, but the photoelectric conversion efficiency is also high, in the outdoor sunlight power generation is more suitable for thin film solar cells, The relative equipment cost is high, but the consumption and battery cost are very low, but the photoelectric conversion efficiency is more than half of that of the crystalline silicon cell, but the weak light effect is very good, and it can also generate electricity under ordinary light, such as the solar cell on the calculator.
4) EVA functions as above, mainly bonded to encapsulate the power generation body and the backplane
5) The backplane function, sealing, insulation, waterproof (generally TPT, TPE and other materials must be resistant to aging, component manufacturers are guaranteed for 25 years, tempered glass, aluminum alloy is generally no problem, the key is whether the backplane and silicone can meet the requirements.)
7) The junction box protects the entire power generation system, plays the role of the current transfer station, if the component short-circuit junction box automatically breaks the short-circuit battery string, prevent burning the entire system junction box the most critical is the selection of the diode, according to the type of battery in the component, the corresponding diode is not the same.
8) silicone sealing effect, used to seal components and aluminum alloy frame, components and junction box junction some companies use double-sided tape, foam to replace silicone, the domestic common use of silicone, simple process, convenient, easy to operate, and the cost is very low.
Solar cells from the laboratory to the factory, experimental research to large-scale production is the road to its development, so can achieve the characteristics of industrial production should be:
[1] The battery production process can meet the assembly line operation;
[2] Capable of large-scale and modern production;
[3] Achieve high efficiency and low cost.
The main goal, of course, is to reduce the production cost of solar cells. The main development direction of polycrystalline silicon cells is towards large area and thin substrate. For example, 125×125mm2, 156×156mm2 and even larger single-piece batteries can be seen on the market, and the thickness is reduced from the original 300 microns to 250, 200 and 200 microns. The efficiency has been greatly improved. Japan's Kyocera (Kyocera) 150×150 battery small batch production of photoelectric conversion efficiency reached 17.1%, the company's production in 1998 reached 25.4MW.
(1) Screen printing and related technologies
Polycrystalline silicon cells are widely used in large-scale production
Screen printing process
The process can be used for printing of diffusion sources, front metal electrodes, back contact electrodes,
Antireflection film
With the improvement of screen materials and the improvement of process level, screen printing process will be more widely used in the production of solar cells.
a. Formation of launch area
PN junction is formed by screen printing instead of the conventional tube furnace diffusion process. Generally, a phosphate-containing paste is printed on the front of the polysilicon, and a metal paste containing aluminum is printed on the back. After printing is completed, diffusion can be completed in the mesh belt furnace (usually at 900 degrees), so that printing, drying, and diffusion can form continuous production. The emission region formed by screen printing diffusion technology is usually relatively high surface concentration, and the surface photogenerated carrier recombination is larger. In order to overcome this shortcoming, the following selection of emission region technology is used in the process, so that the conversion efficiency of the battery is further improved.
b. Select the launch area process
In the diffusion process of polysilicon cells, the selective emission zone technology can be divided into local corrosion or two-step diffusion method. Local corrosion is the removal of the heavy diffusion layer in the area between the metal electrodes by dry methods (such as reactive ion corrosion) or chemical corrosion. Initially, Solarex applied reactive ion corrosion in the same device, first using high reaction power to corrode the heavy doping layer between metal electrodes, and then depositing a silicon nitride film with low power, which plays the dual role of anti-reflection and passivation of the battery surface. Cells with a conversion efficiency of more than 13% on 100cm2 polycrystals. In the same area, the two-part diffusion method is applied, and the conversion efficiency reaches 16% without mechanical suede.
c. Formation of back surface field
The back PN junction is usually formed by screen printing A slurry and hot annealing in the mesh belt furnace. While forming the back surface junction, the process has a good absorption effect on the impurities in the polysilicon. The aluminum impurity absorption process is generally completed in the high temperature section. A good back surface field can obviously increase the open circuit voltage of the battery.
d. Screen printed metal electrode
In large-scale production, the screen printing process has more advantages than vacuum evaporation, metal plating and other processes, in today's process, the positive printing material is generally used to contain silver slurry, the main reason is that silver has good electrical conductivity, weldability and low diffusion properties in silicon. The electrical conductivity of the metal layer formed by screen printing and annealing depends on the chemical composition of the slurry, the content of the glass body, the roughness of the screen, the sintering conditions and the thickness of the screen plate. At the beginning of 1980, screen printing has some defects, I) such as the gate line width is large, usually greater than 150 microns; Ⅱ) Resulting in large shading and low battery filling factor; Iii) It is not suitable for surface passivation, mainly because the surface diffusion concentration is higher, otherwise the contact resistance is larger. Today, advanced methods can be used to screen print a grid line with a line width of 50 microns, a thickness of more than 15 microns, and a block resistance of 2.5~4mΩ, which can meet the requirements of high-efficiency batteries. Some people have compared the solar cell made by screen printing electrode and evaporation electrode on 15×15 square cm Mc-si, and there is almost no difference in the parameters.
About the absorption of light
For light absorption is mainly:
(1) Reduce surface reflection;
(2) Change the path of light in the battery;
(3) Use back reflection.
Polycrystalline silicon solar cells
[1] Laser grooving
It can be made on the surface of polysilicon by means of laser grooving
Inverted pyramid structure
In the spectral range of 500 ~ 900nm, the reflectivity is 4 ~ 6%, which is equivalent to the surface production of double-layer anti-reflection film. The reflectance of suede made by monocrystalline silicon on (100) surface is 11%. The short circuit current of the battery made by laser is about 4% higher than that of the battery coated with double-layer anti-reflection film (ZnS/MgF2) on the smooth surface, which is mainly because the long-wave light (wavelength greater than 800nm) is slanted into the battery. The problem of laser suede production is that in etching, the surface causes damage while introducing some impurities, and the surface damage layer should be removed by chemical treatment. The solar cell made by this method usually has a high short circuit current, but the open circuit voltage is not too high, the main reason is that the increase of the battery surface area causes the increase of the composite current.
[2] Chemical grooving
Application of mask (Si3N4 or SiO2) isotropic corrosion, corrosion solution can be acidic corrosion solution, but also can be a higher concentration
Sodium hydroxide
or
Potassium hydroxide
Solution, the method is unable to form the kind of sharp cone-like structure formed by anisotropic corrosion. It is reported that the suede formed by this method has obvious anti-reflection effect on the spectral range of 700 ~ 1030 microns. However, the mask layer is generally formed at a higher temperature, which causes the performance of the polysilicon material to decline, especially for the lower quality
Polycrystalline material
The life span of minority children is shortened. The conversion efficiency of the cell made on 225cm2 polysilicon is 16.4%. The mask layer can also be formed by screen printing.
[3] Reactive ion corrosion (RIE)
Polycrystalline silicon solar cells
[4] Make anti-reflection film layer
For high-efficiency solar cells, the most commonly used and effective method is to evaporation ZnS/MgF2 double-layer anti-reflection film, the optimal thickness depends on the thickness of the underlying oxidation layer and the characteristics of the battery surface, for example, the surface is smooth or suave, anti-reflection processes also include evaporation Ta2O5, PECVD deposition Si3N3 and so on. ZnO conductive film can also be used as anti-reaction material.
Metallization technique
In the production of high-efficiency batteries, the metallized electrode must be matched with the design parameters of the battery, such as surface doping concentration, PN junction depth, and metal material. The general area of laboratory batteries is relatively small (area less than 4cm2), so you need a fine metal gate line (less than 10 microns), the general method is lithography,
Electron beam evaporation
, electronic plating.
Large-scale industrial production
Electroplating is also used in China, but when evaporation and lithography are combined, they are not low-cost process technologies.
[1] Electron beam evaporation and electroplating
Generally, the application of positive adhesive stripping process, evaporation Ti/Pa/Ag multi-layer metal electrode, to reduce the series resistance caused by the metal electrode, often require a relatively thick metal layer (8 to 10 microns). The disadvantage is that electron beam evaporation causes damage to the silicon surface/passivation layer interface, so that the surface composite is improved, therefore, in the process, the short-time evaporation Ti/Pa layer is used in the process of evaporation silver layer. Another problem is that when the metal and silicon contact surface is large, it will inevitably lead to an increase in the rate of recombination of minority particles. In the process, the method of tunnel junction contact is used to form a thin oxide layer (generally about 20 microns in thickness) between silicon and metal. The application of metals with low work function (such as titanium, etc.) can induce a stable electron accumulation layer on the silicon surface (a fixed positive charge can also be introduced to deepen the inverse). Another method is to open a small window (less than 2 microns) on the passivation layer, and then deposit a wide metal gate line (usually 10 microns) to form a mushroom - like electrode. By using this method, the conversion efficiency of the cell on 4cm2 Mc-Si reaches 17.3%. In addition, the Shallow angle (oblique) technique is also used on the mechanical grooving surface.
Formation method
[1] Emission zone formation and phosphorus absorption
For high-efficiency solar cells, the formation of the emission zone is generally adopted by selective diffusion, which forms a heavy impurity region under the metal electrode and achieves shallow concentration diffusion between the electrodes. The shallow concentration diffusion of the emission zone enhances the response of the battery to blue light, and makes the silicon surface easy to passivation. The diffusion methods include two-step diffusion process, diffusion plus corrosion process and burial diffusion process. Today, with selective diffusion, the conversion efficiency of the 15×15cm2 battery reaches 16.4%, the surface of the n++ and n+ regions
Block resistance
It's 20Ω and 80Ω.
For Mc-si materials, the effect of phosphorus expansion on the battery has been extensively studied, and a longer phosphorus absorption process (generally 3 to 4 hours) can increase the minority diffusion length of some Mc-si by two orders of magnitude. In the study of the effect of substrate concentration on the absorption of impurities, it was found that even for the high concentration of the lining material, a large minority diffusion length (greater than 200 microns) can be obtained through the absorption of impurities, the open circuit voltage of the battery is greater than 638mv, and the conversion efficiency is more than 17%.
Polycrystalline silicon battery module
[3] Double-sided Mc-si battery
The front side of the Mc-si double-sided battery is a conventional structure, and the back side is a structure of N+ and P+ crossing each other, so that the photolions generated by the front light but located near the back side can be effectively absorbed by the back electrode. The back electrode, as an effective complement to the front electrode, also acts as an independent carrier collector for back light and scattered light, with a reported conversion efficiency of more than 19% at AM1.5.
For Mc-si, due to the existence of high grain boundaries, point defects (vacancy, interstitial atoms, metal impurities, oxygen, nitrogen and their complexes) are particularly important for the passivation of defects on the surface of materials and in vivo. In addition to the above-mentioned impurity absorption technology, passivation process has a variety of methods, and saturated silicon suspension bonds through thermal oxidation is a more common method. The passivation effect depends on the surface concentration of the emission region, the interfacial state density and the floating cross section of electrons and holes. Annealing in hydrogen atmosphere can make the passivation effect more obvious. The use of PECVD to deposit the silicon nitride front is very effective because of the effect of hydrogenation during film formation. The process can also be applied to large-scale production. Using Remote PECVD Si3N4, the surface recombination speed can be less than 20cm/s.
Polysilicon solar cells are favored for their abundant raw materials, low cost, high conversion efficiency, good stability and other advantages, and also meet the needs of society to occupy the main share of the solar cell market.
[3]
The center of gravity has developed from single crystal to polycrystal, mainly because:
[1] There is less and less head-and-tail material to supply solar cells;
[2] For solar cells, square substrates are more cost-effective, through
Casting method
And the polysilicon obtained by the direct solidification method can directly obtain the square material;
[3] The production process of polysilicon continues to make progress, and the automatic casting furnace can produce more than 200 kg of silicon ingot per production cycle (50 hours), and the grain size reaches the centimeter level;
Polycrystalline silicon solar cell modules
(1) Because the output power of the solar module depends on
Solar irradiance
Therefore, the measurement of the solar cell module is carried out under standard conditions (STC), which is defined as: atmospheric quality AM1.5, light intensity 1000W/m2, and temperature 25℃.
(2) Under such conditions,
Solar cell module
The maximum power output is called the peak power, and in many cases, the peak power of the module is usually determined with a solar simulator. The main factors affecting the output performance of solar modules are as follows:
1) Load impedance
2) Sunshine intensity
3) Temperature
4) Shadows
Solar panel
The data provided by the manufacturer is guaranteed for 25 years.
Solar AC power generation system is composed of solar panels, charging controllers, inverters and batteries; Solar DC power generation systems do not include inverters. In order to make the solar power generation system can provide enough power for the load, it is necessary to choose the components reasonably according to the power of the electrical appliances. The following takes 100W output power and 6 hours a day as an example to introduce the calculation method:
1. First of all, the watt-hours consumed per day (including the loss of the inverter) should be calculated: if the conversion efficiency of the inverter is 90%, when the output power is 100W, the actual output power should be 100W/90%=111W; If used for 5 hours per day, the power consumption is 111W*5 hours =555Wh.
2. Calculation of solar panels: according to the daily effective sunshine time is 6 hours, and then taking into account the charging efficiency and loss during the charging process, the output power of solar panels should be 555Wh/6h/70%=130W. 70% of this is the actual power used by solar panels during the charging process.
In order to reduce the production cost of solar grade polysilicon, thereby reducing the cost of solar cell manufacturing and promoting the development of solar photovoltaic industry.
[4]
(1) Small power supply ranging from 10-100W, used in remote areas without electricity such as plateaus, islands, pastoral areas, border posts and other military and civilian life electricity, such as lighting, television, radio recorders, etc.; (2) 3-5KW household roof grid-connected power generation system; (3) Photovoltaic water pump: solve the problem of deep water well drinking and irrigation in areas without electricity.
Second, the field of transportation
Such as
Beacon light
, traffic/railway signal lights, traffic warning/sign lights, Yuxiang street lights,
Altitude obstacle light
Highway/railway wireless phone booths, unattended road shift power supply, etc.
3. Communications/communication field
Solar unattended microwave relay station, optical cable maintenance station, broadcast/communication/paging power system; village
Carrier telephone
Photovoltaic system, small communication machine, soldier GPS power supply, etc.
4. Petroleum, Marine and meteorological fields
Oil pipeline and reservoir gate cathodic protection solar power system, oil drilling platform living and emergency power supply, ocean detection equipment, meteorological/hydrological observation equipment, etc.
Five, home lighting power supply
Such as garden lights, street lights, hand lights, camping lights, mountaineering lights, fishing lights, black lights, rubber cutting lights, energy-saving lamps and so on.
6. Photovoltaic power station
10KW-50MW independent photovoltaic power station, wind (firewood) complementary power station, various large parking plant charging stations.
7. Solar energy building
The combination of solar power generation and building materials, so that the future of large buildings to achieve self-sufficiency in electricity, is a major future development direction.
8. Other areas include
(1) With the car: solar car/electric car, battery charging equipment, car air conditioning, ventilation fan, cold drink box, etc.; (2) Solar hydrogen and fuel cell regenerative power generation system; (3)
Seawater desalination plant
Power supply; (4) Satellites, spacecraft, space solar power plants, etc.
