In recent years, under the guidance of the photovoltaic leader program, the trend of China's photovoltaic market to become more efficient is obvious. All kinds of high-efficiency components have achieved good market share with excellent performance, of which PERC components are the most popular. Under the active expansion of production by domestic first-line manufacturers such as Longji, Xiexin, Jingke, Jingao, Tianhe and Artes, the current high-efficiency PERC battery has a great potential to lead the photovoltaic market.
Recently Longji Co. Ltd. has broken through the photoelectric conversion efficiency of single crystal PERC battery to 22.71%, setting a new PERC battery world record. It is understood that Longji Co., Ltd. plans to convert the current 5GW single crystal module production capacity to PERC production line in the second quarter of next year. Xiexin Integration announced a few days ago that it has effectively solved the recession problem of polycrystalline PERC batteries. Its high-efficiency polycrystalline black silicon PERC battery production capacity has exceeded 1GW and is expected to reach 2GW by the end of the year.
Experts believe that the efficiency of single crystal PERC may increase to 24%, and PERC will become the mainstream of photovoltaic market in the next three to five years. According to the forecast of authoritative organizations, PERC production is expected to reach 20GW by the end of 2017, and by 2020, PERC production will reach 65 GW, with shipments accounting for 50% of the entire photovoltaic market. In addition to its technological advantages and development potential, PERC's success is inseparable from its promotion in the PV leader project in 2015.
According to the latest "leader" plan, the third batch of leader bases will be divided into application leader bases and technology leader bases. Among them, the emergence of technology leader bases is to promote those frontier technologies with development potential, using frontier technologies or breakthrough technology products that have been independently developed and not yet applied in the market. According to the Notice on Promoting the Implementation of the "Leader" Plan for Photovoltaic Power Generation and Relevant Requirements for the Construction of Leading Bases in 2017 issued by the State Energy Administration, the Technology Leading Bases will accelerate the application and transformation of scientific and technological research and development achievements, promote and lead the technological progress and market application of photovoltaic power generation by providing experimental demonstration and supporting projects for leading-edge technological products that can be independently innovated and developed by photovoltaic manufacturing enterprises but have not yet been mass-produced. From the point of view of product manufacturing, the technology leading base adopts products that have not yet completed production lines and formed production capacity. For advanced technology products with existing production lines and formed production capacity, it does not belong to the scope of support.
Obviously, the technology leading base is mainly to support those frontier technologies that have not yet completed production lines. Combined with PERC's development curve, the frontier technologies selected by the frontrunner will most likely take this opportunity to achieve rapid development and bring efficiency changes to the industry. After PERC, who will be the next "leader" in photovoltaic technology?
At present, crystalline silicon battery is still the mainstream in the market, and to improve the conversion efficiency of crystalline silicon battery, it is generally realized through two aspects of improvement. The first is to increase the light absorption of the battery, such as the light trap structure, that is, to increase the light absorption efficiency of the battery by means of chemical etching or texturing. The second is to improve the efficiency of the battery by effectively separating photo-generated carriers and reducing carrier recombination. Common methods include increasing back field, increasing passivation layer, improving substrate materials, etc. The following are some battery cutting-edge technologies under development listed by Xiao Bian for reference.
1. IBC battery
IBC cell, i.e. all back electrode contacts crystalline silicon photovoltaic cell, uses N-type substrate material. The IBC battery has the advantage that the metal contacts of the positive and negative electrodes are on the back of the battery sheet, so that the metal grid lines of the traditional photovoltaic battery on the front surface are completely invisible on the battery surface, thus not only increasing the effective contact area of the battery and greatly increasing the conversion efficiency of the battery, but also the front surface of the battery without the grid lines is more beautiful in appearance.
The concept of IBC battery was first proposed by Lammert and Schwartz in 1975. After decades of development, the conversion efficiency of IBC cells has reached 25% under a standard solar test condition, far exceeding that of crystalline silicon solar cells. Japanese Panasonic Company combined IBC technology with HIT technology in 2014, and developed HIT-IBC solar cell with a maximum efficiency of 25.6%, breaking the world record for crystalline silicon cell conversion efficiency.
U.S. SunPower was the first company to realize IBC battery mass production, with the highest conversion efficiency of 25% and the average mass production efficiency of 23%. Domestic enterprises such as Trina, Jingao and Hairun have invested in the research and development of IBC battery technology, among which Trina Solar has continuously broken the world record and set the maximum conversion efficiency of large-area IBC batteries at 24.13%. In addition, the efficiency of the small-area IBC battery jointly developed by SkyTeam and Australian National University (ANU) reached 24.37%.
Due to the complicated manufacturing process and high cost of materials used, IBC battery has not yet been produced on a large scale in China. However, IBC battery has high conversion efficiency and outstanding power generation capacity, which makes it have a good development space and may become a new technology leading the development of the industry in the future.
2. HIT battery
The hit cell is an intrinsic thin-film heterojunction. Unlike conventional batteries, where the p-n junction consists of crystalline silicon of the same material with opposite conductivity types, HIT batteries' p-n junction consists of two different semiconductor materials-amorphous silicon/crystalline silicon. It has both front and back sides that can generate electricity when exposed to light. The low-temperature manufacturing process has the advantages of protecting carrier life, high open circuit voltage, good temperature characteristics and the like.
In 1992, Makoto Tanaka and Mikio Taguchi of Sanyo Company successfully prepared HIT batteries for the first time. Japan's Panasonic Company continued to develop HIT batteries after acquiring Sanyo Company in 2009. The highest conversion efficiency of the laboratory reached 24.7%.
In terms of mass production, it is reported that Panasonic of Japan has a total HIT capacity of 1GW, and the conversion efficiency of battery mass production is about 22.5%. It is understood that the HIT module, which was first put into use, has been in use for about 11 years and its cumulative attenuation is only 2%~3%.
Each step of HIT battery production process requires very strict technology, and has high requirements on the surface cleaning and purification, low temperature technology and materials of the front crystalline silicon. In addition, the cost of related materials is still relatively high, so under the condition of ensuring high efficiency, the large-scale mass production of HIT batteries needs further breakthroughs and development.
3. Double-sided N-type battery
N-type batteries are the development direction of high-efficiency batteries in the future. Currently, the N-type single crystal high-efficiency batteries studied mainly include PERT batteries, PERL batteries, HIT batteries, IBC batteries, HBC batteries, etc. PERT batteries and PERL batteries can be divided into single-side light-receiving type and double-side light-receiving type according to their light-receiving surfaces. The back of the double-sided N-type battery can receive reflected light, and the total power generation can be increased by more than 3% by combining the double-sided glass assembly technology. The n-PERL battery in mitsubishi electric adopts a double-sided light-receiving structure, realizing a conversion efficiency of 21.3% on a 156*156mm2 large-area monocrystalline silicon wafer.
Yingli's PANDA battery is a large area battery (239cm2) with a double-sided light-receiving PERT structure. PANDA battery is designed to generate electricity on both sides, and can receive light entering the battery from both the front and the back so as to realize the function of generating electricity on both sides. The front side adopts the design of fine grid lines, which reduces the shading area and improves the short-circuit current of the battery. Yingli's PANDA battery has been mass produced with a maximum conversion efficiency of 21.3%. Compared with large-scale production of IBC, HIT and other N-type batteries, PANDA battery has the advantages of simple structure, low preparation cost and short process flow, is compatible with the existing P-type production line, and is easy to realize large-scale mass production.
In addition, the combination of various technologies is also a hot topic of recent research. For example, the combination of PERC+ black silicon and other technologies also has great development prospects in the future. Who can become the next "leader" in photovoltaic technology depends on the perfection of production technology and the reduction of cost. What is needed before this is for enterprises to step up research and development efforts and speed up the development of innovative technology demonstration production lines, so as to promote the latest technology.