Solar cell module parameters and production process

Solar cells are divided into single crystal cells and polycrystalline cells.

Classification

Domestically used solar crystalline silicon cells can be classified according to size and single polycrystal:

Single crystal 125*125

Single crystal 156*156

Polycrystalline 156*156

Single crystal 150*150

Single crystal 103*103

Polycrystalline 125*125

Related components

125*125 single crystal

Introduction to the excellent performance of crystalline silicon solar cells:

·High efficiency, low attenuation and high reliability;

· Advanced diffusion technology ensures good uniformity within the film and reduces the matching loss between the cells;

·Using advanced tubular PECVD film forming technology, the deep blue silicon nitride anti-reflection film covering the surface of the battery is dense, uniform and beautiful;

? Apply high quality metal paste to make electrodes and back fields. Ensures good electrical conductivity, solderability and flatness of the back field;

High-precision screen printing graphics make the cell easy to solder automatically.

156*156 polycrystalline

Introduction to the excellent performance of crystalline silicon solar cells:

In addition to the excellent performance of the 125*125 single crystal battery the following performance is also available.

High-precision screen printing graphics make the cell easy to solder automatically.

125 single crystal

Introduction to the excellent performance of crystalline silicon solar modules:

· SF-PV components can meet different levels of consumption

· Use high efficiency silicon solar cells

·Component nominal voltage 24/12VDC

·3.2mm thick tempered glass

· To improve wind resistance and snow pressure, use a durable aluminum frame for easy assembly.

·The frame of the component is designed with a leaking hole for drainage to eliminate the long-term accumulation of rain or snow in the winter, causing icing or even deforming the frame.

· Cables are assembled using quick connectors

·Packaging to meet customer requirements

· Guarantee 25 years of service life

156 polycrystal

Excellent performance of crystalline silicon solar cell modules: excellent performance with 125 single crystals

Solar cell manufacturing process

The production process of solar cells is divided into silicon wafer inspection - surface texturing and pickling - diffusion bonding - dephosphorization silicon glass - plasma etching and pickling - anti-reflection coating - screen printing - Rapid sintering, etc. The details are as follows:

First, silicon wafer inspection

The silicon wafer is the carrier of the solar cell sheet. The quality of the silicon wafer directly determines the conversion efficiency of the solar cell sheet, so it is necessary to detect the incoming silicon wafer. This process is mainly used to measure some technical parameters of the silicon wafer. These parameters mainly include the surface roughness of the silicon wafer, minority lifetime, resistivity, P/N type and microcrack. The equipment is divided into automatic loading and unloading, silicon wafer transmission, system integration and four detection modules. Among them, the photovoltaic wafer detector detects the unevenness of the surface of the silicon wafer, and simultaneously detects the appearance parameters such as the size and diagonal of the silicon wafer; the microcrack detection module is used to detect the internal microcrack of the silicon wafer; The detection module, one of the online test modules mainly tests the silicon wafer resistivity and the silicon chip type, and the other module is used to detect the minority carrier lifetime of the silicon wafer. Before performing the minority carrier lifetime and resistivity detection, it is necessary to detect the diagonal and micro crack of the silicon wafer and automatically remove the damaged silicon wafer. The wafer inspection equipment is capable of automatically loading and unloading sheets, and can place defective products in a fixed position, thereby improving detection accuracy and efficiency.

Second, the surface of the cashmere

Monocrystalline silicon suede is prepared by the anisotropic etching of silicon, which forms millions of tetrahedral pyramids, ie pyramid structures, per square centimeter of silicon surface. Due to the multiple reflections and refractions of the incident light on the surface, the absorption of light is increased, and the short-circuit current and conversion efficiency of the battery are improved. The anisotropic etching solution of silicon is usually a hot alkaline solution, and the usable bases are sodium hydroxide, potassium hydroxide, lithium hydroxide and ethylenediamine. Most of the low-temperature sodium hydroxide solution is used to prepare fumed silicon at a corrosion temperature of 70-85 ° C. In order to obtain uniform suede, alcohols such as ethanol and isopropanol should be added as a complexing agent in the solution to accelerate the corrosion of the silicon. In the preparation of the velvet, the silicon wafer must first be subjected to preliminary surface corrosion, etched with an alkaline or acidic etching solution to about 20 to 25 μm and after the corrugated surface is subjected to general chemical cleaning. Surface-prepared silicon wafers should not be stored in the water for a long time to prevent contamination and should be diffused as soon as possible.

Third, diffusion and knot

Solar cells require a large area of PN junction to convert light energy to electrical energy, and the diffusion furnace is a specialized device for manufacturing solar cell PN junctions. The tubular diffusion furnace mainly consists of four parts: the upper download part of the quartz boat, the exhaust gas chamber, the furnace part and the gas cabinet part. Diffusion generally uses a liquid source of phosphorus oxychloride as a diffusion source. P-type silicon wafer is placed in a quartz container of a tube diffusion furnace, and phosphorus oxychloride is introduced into a quartz container at a high temperature of 850---900 degrees Celsius, and reacted by phosphorus oxychloride and silicon wafer to obtain phosphorus atom. After a certain period of time, the phosphorus atoms enter the surface layer of the silicon wafer from all sides, and diffuse into the inside of the silicon wafer through the gap between the silicon atoms, forming an interface between the N-type semiconductor and the P-type semiconductor, that is, the PN junction. The PN junction prepared by this method has good uniformity, the square resistance is less than ten percent, and the minority lifetime can be greater than 10 ms. Manufacturing PN junctions is the most basic and critical process in solar cell production. Because it is the formation of the PN junction, the electrons and holes do not return to the original position after flowing, thus forming a current and the current is led out by the wire, which is direct current.

Fourth, dephosphorus glass

The process is used in the production process of a solar cell sheet, and the silicon wafer is immersed in a hydrofluoric acid solution by a chemical etching method to generate a chemical reaction to form a soluble complex hexafluorosilicic acid to remove the diffusion system. A layer of phosphosilicate glass formed on the surface of the silicon wafer after the junction. During the diffusion process, POCL3 reacts with O2 to form P2O5 deposited on the surface of the silicon wafer. P2O5 reacts with Si to form SiO2 and phosphorus atoms.

Thus, a layer of SiO2 containing phosphorus is formed on the surface of the silicon wafer, which is called a phosphosilicate glass. The equipment for removing phosphorus-silicone glass is generally composed of a body, a cleaning tank, a servo drive system, a mechanical arm, an electric control system, and an automatic acid distribution system. The main power sources are hydrofluoric acid, nitrogen, compressed air, pure water, and hot exhaust wind and wastewater. Hydrofluoric acid is capable of dissolving silica because hydrofluoric acid reacts with silica to form a volatile silicon tetrafluoride gas. If the hydrofluoric acid is excessive, the silicon tetrafluoride formed by the reaction will further react with hydrofluoric acid to form a soluble complex hexafluorosilicic acid.

Fifth, plasma etching

Since even the back-to-back diffusion is used during the diffusion process, all surfaces including the edges of the silicon wafer will inevitably diffuse with phosphorus. The photogenerated electrons collected on the front side of the PN junction flow along the edge where the phosphorus diffuses to the back of the PN junction, causing a short circuit. Therefore, the doped silicon around the solar cell must be etched to remove the PN junction at the edge of the cell. This process is usually done using plasma etching techniques. The plasma etching is performed under low voltage, and the parent molecule of the reaction gas CF4 is ionized and forms plasma under the excitation of radio frequency power. The plasma is composed of charged electrons and ions. Under the impact of electrons, the gas in the reaction chamber absorbs energy and forms a large number of active groups in addition to being converted into ions. The reactive group reaches the surface of the SiO2 due to diffusion or under the action of an electric field, where it chemically reacts with the surface of the material to be etched, and forms a volatile reaction product which is separated from the surface of the object to be etched and is evacuated to the cavity by the vacuum system.

Sixth, anti-reflection film

The reflectivity of the polished silicon surface is 35%. In order to reduce the surface reflection and improve the conversion efficiency of the battery, it is necessary to deposit a silicon nitride anti-reflection film. In industrial production, antireflection films are often prepared using PECVD equipment. PECVD is plasma enhanced chemical vapor deposition. Its technical principle is to use low temperature plasma as the energy source, the sample is placed on the cathode of the glow discharge under low pressure, the sample is heated to a predetermined temperature by glow discharge, and then the appropriate amount of reaction gases SiH4 and NH3 are introduced. A series of chemical reactions and plasma reactions form a solid film, a silicon nitride film, on the surface of the sample. In general, the film deposited by this plasma enhanced chemical vapor deposition method has a thickness of about 70 nm. Films of this thickness have optical functionality. By using the principle of thin film interference, the reflection of light can be greatly reduced, the short-circuit current and output of the battery are greatly increased, and the efficiency is also considerably improved.

Seven, screen printing

After the process of texturing, diffusion and PECVD, the solar cell has been made into a PN junction, which can generate current under illumination. In order to derive the generated current, it is necessary to make positive and negative electrodes on the surface of the battery. There are many ways to make electrodes, and screen printing is currently the most common production process for making solar cell electrodes. Screen printing is to emboss the predetermined pattern on the substrate by embossing. The device consists of silver aluminum paste printing on the back of the battery, aluminum paste printing on the back of the battery and silver paste printing on the front side of the battery. The working principle is as follows: a part of the mesh pattern is used to pass through the slurry, and a certain pressure is applied to the slurry portion of the screen by the scraper while moving toward the other end of the screen. The ink is squeezed from the mesh of the pattern portion onto the substrate by the doctor blade during movement. Due to the viscous action of the slurry, the print is fixed within a certain range, and the squeegee is always in linear contact with the screen plate and the substrate during printing, and the contact line moves as the blade moves, thereby completing the printing stroke.

Eight, rapid sintering

The screen-printed silicon wafer cannot be used directly, and it needs to be rapidly sintered in a sintering furnace to burn off the organic resin binder, leaving almost a pure silver electrode that is adhered to the silicon wafer due to the vitreous action. When the silver electrode and the crystalline silicon reach the eutectic temperature, the crystalline silicon atoms are incorporated into the molten silver electrode material at a certain ratio, thereby forming an ohmic contact of the upper and lower electrodes, and improving the open circuit voltage and the filling factor of the battery. The key parameters are such that they have resistive properties to improve the conversion efficiency of the cell.

The sintering furnace is divided into three stages: pre-sintering, sintering, and cooling. The purpose of the pre-sintering stage is to decompose and burn off the polymer binder in the slurry. At this stage, the temperature rises slowly. In the sintering stage, various physical and chemical reactions are completed in the sintered body to form a resistive film structure, which makes it truly resistive. At this stage, the temperature reaches a peak; in the cooling and cooling stage, the glass is cooled and solidified, and the resistive film structure is fixedly adhered to the substrate.

Nine, peripheral equipment

In the production process of battery chips, peripheral facilities such as power supply, power, water supply, drainage, HVAC, vacuum, and special steam are also required. Fire and environmental protection equipment is also important to ensure safety and sustainable development. An annual production capacity of 50MW solar cell production line, only the process and power equipment power is about 1800KW. The amount of pure water used in process is about 15 tons per hour, and the water quality requirements meet the EW-1 technical standard of China Electronic Grade Water GB/T11446.1-1997. The amount of process cooling water is also about 15 tons per hour. The particle size of the water should not exceed 10 microns, and the water supply temperature should be 15-20 °C. The vacuum displacement is around 300M3/H at the same time, about 30 cubic meters of nitrogen storage tank and 10 cubic meters of oxygen storage tank are needed. Considering the safety factors of special gases such as silane, it is also necessary to set up a special air room to ensure absolute production safety. In addition, silane combustion towers, sewage treatment stations, etc. are also necessary facilities for the production of battery sheets.

Attention problem

The solar cell uses a co-firing process that requires only one sintering, while forming an ohmic contact of the upper and lower electrodes. Silver wafer, silver aluminum paste, aluminum paste printed silicon wafer, after drying, the organic solvent is completely volatilized, and the film shrinks into a solid substance and adheres to the silicon wafer. At this time, it can be regarded as a metal electrode material layer and silicon. The pieces touch together. When the electrode metal material and the semiconductor single crystal silicon are heated to a eutectic temperature, the single crystal silicon atoms are dissolved in the molten alloy electrode material in a certain ratio. The entire process of dissolving a single crystal silicon atom into the electrode metal is quite fast, typically in a matter of seconds. The number of dissolved single crystal silicon atoms depends on the alloy temperature and the volume of the electrode material. The higher the temperature of the sintered alloy, the larger the volume of the electrode metal material, the more the number of silicon atoms dissolved. The state at this time is called crystal. An alloy system of electrode metals if the temperature is lowered at this time, the system begins to cool to form a recrystallized layer, at which time the silicon atoms originally dissolved in the electrode metal material are crystallized again in a solid state, that is, an epitaxial layer is grown at the metal-crystal contact interface. If the epitaxial layer contains a sufficient amount of impurity components of the same conductivity type as the original crystal material, an ohmic contact is formed by the alloying process; if a sufficient amount of impurity component which is different from the conductivity type of the original crystal material is contained in the crystal layer This results in the formation of a PN junction by an alloy process.

In the general mesh belt type sintering furnace, a heating wire is used as a heating element, and the work piece is mainly heated by heat conduction, and rapid temperature rise cannot be achieved. Only radiation or microwave can quickly heat the object, and radiant heating has the advantages of economical use, safety and reliability, and easy replacement. Therefore, the solar cell sintering furnace basically uses an infrared quartz lamp as the main heating element. Its design needs to pay attention to the following three issues:

1, the structure of the heating tube

In order to achieve a temperature spike in the sintering section, sufficient heating power needs to be placed in a short furnace space. There are two configurations of short wave manifold and short wave single tube, and the linear power density is 60kW/m2. Although the short-wave tube has a higher single power (equivalent to two single tubes in parallel), due to the complicated manufacturing process, the quality of the quartz glass tube is higher, and the manufacturing cost is about 2.5 times that of the single tube. Therefore, in actual use, a single tube is mostly used.

2. Infrared radiation absorption spectroscopy

When the infrared radiation energy is absorbed by the work piece, the absorption spectrum specific to the substance needs to match the emission spectrum to absorb the radiant energy most efficiently in the shortest time. Therefore, the selected infrared quartz lamps are also different at different stages of sintering. In the drying section, it is necessary to use the medium-wave tube to assist the hot air heating in the rapid evaporation of the organic solvent and water. In the pre-burning section, the substrate should be sufficiently uniformly preheated, and the medium-wave tube has good infrared radiation and equilibrium. The absorption and penetration ability meets the requirements; in the sintering section, the substrate must reach the eutectic temperature in a very short time, and only short-wave tubes can do this.

3. Fixing method of heating tube

The temperature of the sintering section is about 850 °C. At this time, the surface temperature of the lamp will reach 1100 °C, which is close to the use limit of the quartz tube. If the pore is slightly overheated, the lamp will be burned immediately. In the lead wire of the lamp tube, since the metal piece of the welding wire and the quartz glass are sealed together, the thermal expansion coefficients of the two are inconsistent. If the temperature is too high, stress cracks may occur, causing the lamp to leak. Therefore, the way in which the lamp is mounted and fixed in the furnace is very important. Figure 2 shows a fixed way of the infrared tube in the furnace. The fixing method requires that the cold end of the lamp tube be at least 80 mm away from the furnace wall, so as to ensure that the temperature of the lead wire portion is not too high; and the diameter of the mounting hole on the furnace wall is 2 to 3 mm larger than that of the lamp tube, and is fixed by both sides. The clamp holds the tube suspended in the furnace.

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