1, HIT battery structure and principle
Hit is the abbreviation of heterojunction with intrinsic Thin-Layer, meaning the heterogeneous knot, because HIT has been applied by the Japanese Sanyo Company as a registered trademark, so it is also known as HJT or SHJ (Silicon Heterojunction Solar Cell). The type of solar cell was first successfully developed by Japan Sanyo Company in 1990. The conversion efficiency can reach 14.5% (4mm2 battery). Later, under the continuous improvement of Sanyo Company, Sanyo Hit battery conversion efficiency has reached 2015 25.6%. In 2015, the HIT patent protection of Sanyo, the elimination of technical barriers, which is a great time to develop and promote HIT technology.
The figure below is the basic configuration of the HIT solar cell, characterized in that the P-I type A-Si: H membrane (film thickness 5-L0 nm) and I-N-N-N-type A-Si: H film on the back side ( The film thickness 5-L0 nm depends on the crystal silicon sheet, forms a transparent electrode and a collector at both sides, constitute a HIT solar cell having a symmetrical structure.
Chart: HIT Solar Battery Structure Schematic
On the front surface of the battery, since the band is bent, the electron movement is blocked, and the hole can be tunneled by a highly doped p + -ty-type amorphous silicon due to the etholate layer. Similarly, on the back surface, since the movement of the hole to the back surface is blocked, the electrons can be tunted to tunneling, and the electron transport layer is constituted by highly doped N +-type amorphous silicon. The selective transport layer is deposited by the battery is in front of the battery, so that the photovoltaic carrier can only produce an enriched in the absorbent material and then flow from one surface of the battery, thereby achieving the separation of both.
2, HIT battery process flow
A great advantage of the HIT battery is relatively simple in process steps, with a total of four steps: phenar, amorphous silicon film deposition, TCO preparation, electrode preparation.
Chart 2: HIT Solar Battery Process Process
The core process of prepared is a deposition of amorphous silicon films, which requires a major challenge to process cleanliness requirements, reliability and reproducibility during mass production, usually prepared with PECVD.
The HIT battery has a simple process step, and the process temperature is low, and the damage of the high temperature process to silicon wafers can be avoided, and the discharge is effectively reduced, but the process is difficult, and the production line is not compatible with traditional batteries. It is more equipment asset investment.
3, HIT battery advantages and features
The HIT battery has the advantage of high power generation and low degree of electricity, and the specific features are as follows:
(1) Low temperature process
The HIT battery combines the advantages of film solar cells (<250 °="" c),="" thereby="" avoiding="" the="" use="" of="" conventional="" high="" temperatures="" (=""> 900 ° C) diffusion process to obtain P-N junction. This technology not only saves energy, but also low temperature environments such that the H-based thin film is doped, the width and thickness of the H-based film can be more accurately controlled, and the device characteristics are also easy to optimize the device characteristics; during low temperature deposition, the single product wafer bending deformation Small, thus its thickness can use the lowest value (about 80 μm) required by the light absorbing material; and the low temperature process eliminates the performance degradation of the silicon substrate in high temperature treatment, thereby allowing "low quality" crystalline silicon or even polysilicon To make a substrate.
The high temperature environment is high. In a day, the power generation of the HIT battery is 8-10% higher than that of the general crystal silicon solar cell, and the dual glass Hit assembly is more than 20%, which has higher users. value.
(2) Double-sided battery
HIT is a very good double-sided battery, the front and back is basically free of color difference, and the double-sided rate (the ratio of the backup efficiency and positive efficiency) can reach more than 90%, up to 96%, and the strength of the back is obvious.
(3) High efficiency
The HIT battery has a heterojunction structure with a thin layer of thin layers, and the surface passivation of single crystal silicon is completed while the p-N is junction, which greatly reduces the surface, and the interfacial leakage current increases the battery efficiency. At present, the laboratory efficiency of HIT batteries has reached 23%, and the battery efficiency of the commercially available 200W component reached 19.5%.
(4) High stability
The light stability of the HIT battery has indicated that the amorphous silicon film in the non-silicon film / crystalline silicon heterojunction did not find the Staebler-Wroni effect, so that there is no such as amorphous silicon solar cell conversion efficiency due to illumination. The phenomenon of recession; the temperature of the HIT battery is good, compared with the temperature coefficient of the single crystal silicon battery - 0.5% / ° C, the temperature coefficient of the HIT battery can reach -0.25% / ° C, so that the battery is in light There is still good output in the temperature rise.
(5) No photoloration attenuation
One of the most important issues that plague the crystalline solar cell is photolithosis, and the HIT battery has naturally no attenuation, and even a degree of efficiency is increased, and the Shanghai micro-system is found to be found in the experiment, after the light The battery conversion efficiency increased by 2.7%, and the attenuation phenomenon is also not present after continuous illumination. Japanese CIC, Switzerland EPFL, CSEM Joint Published on APL also confirmed the photochromic characteristics of the HIT battery.
(6) Symmetry structure is suitable for thin film
The perfect symmetry structure and low temperature process of HIT batteries makes it very suitable for thin film, and the Shanghai micro-system has been found that the thickness of the silicon wafer is in the range of 100-180 μm, and the average efficiency is almost unchanged. The 100μm thickness silicon wafer has been achieved. More than 23% of the conversion efficiency is currently undergoing mass production of 90 μm silicon wafers. Battery sheet can not only reduce the cost of silicon wafer, but it can also be more diverse.
(6) Low cost
The thickness of the HIT battery can save silicon materials; low temperature processes can reduce energy consumption, and allow for inexpensive substrates; high efficiency such that the area of the battery can be reduced under the same output power, thereby effectively reduces the cost of the battery.
4, HIT battery industrialization status
The data shows that in terms of large-scale mass production, the first none of the none of course is Japanese Sanyo, the existing capacity is 1GW, and the mass production efficiency is 23%. In addition, there are more mature HIT technology, Keneka, Sunpreme, SolarCity, Fujian average stone, Jinneng, New Olympic, Hanneng and other enterprises.
Chart: HIT solar cell industrialization at home and abroad (unit:%, MW)
At present, the mass production difficulties of Hit products mainly include the following aspects:
(1) High-quality silicon sheet: Compared to conventional n-type products, HIT batteries have higher requirements for silicon wafers, and they need to be cautious in which silicon suppliers are selected.
(2) Control of surface cleanliness of the velvet after the velvet: HIT battery is very high on the surface cleanliness of the silicon wafer, and it is necessary to balance the degree of cleaning of the silicon cleaning and related chemicals and water consumption.
(3) Each step Q-Time Control: The HIT battery is more harsh than the time of exposure of the silicon wafer before completion of the amorphous silicon coating, and needs to pay attention to the control of the Q-Time of each step.
(4) Effect of production continuity for TCO coating equipment: TCO coating must ensure continuous feed, otherwise the quality and equipment status will be affected, especially when the production line has been put into production, maintaining production continuity is a major challenge.
(5) Continuous printing stability of high viscosity slurries: During the preparation of HIT batteries, there are many virtual printing gates that are highly caused by the slurry viscosity, and it takes several times to the conventional production line.
(6) Stability of the soldering tension: the tensile stable window narrow, the components structure of the bibior double-sided power generation further increases the difficulty of the battery series.
In addition, one of the important factors affecting HIT industrialization is the cost problem. According to Dr. Yang Liyou, the HIT battery BOM cost is a silicon wafer, conductive silver paste, target, velvet additive. For these high-cost parts, special reducing books, including reducing the consumption of raw materials, localization of key equipment, localization of key raw materials, introduction of new technologies.
5, HIT battery market prospects
Educated to the elaboration is always the eternal theme of the photovoltaic industry. As the industry continues to technological progress and policies, the public's eyes gradually transferred to the electricity cost, and the high-efficiency battery has attracted attention. After the PERC battery became a hot spot, HIT battery technology had a breakthrough, and the cost-effective advantage began to appear, and the future will be the era of PERC batteries and N-type HIT batteries.
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