Introduction: Double-sided components can be divided into P-type double-sided and N-type double-sided according to the different crystalline silicon substrates. The current double-sided battery structures that can be mass produced are mainly P-type PERC double-sided, N-PERT double-sided and HIT .
"This year will be the first year of rapid development of double-sided components." Many industry experts have expressed this view. Bloomberg New Energy Finance had previously expected that the market size of the double-sided battery module will reach 3GW in 2018, mainly for leading projects. After the 531 New Deal, the leader project has become one of the main domestic demand markets in the second half of the country. Among them, the total number of double-sided components in the application leader is about 2. 6GW, accounting for 52%; three bases of technology leaders 6 Four of the bidding sections have declared double-sided technology. Although the current proportion of double-sided module shipments is still very small, it can be seen from the SNEC exhibition and the leader project that the layout of double-sided technology has become a force for photovoltaic companies, and double-sided technology is fast development of.
Who is the "son of heaven" for double-sided technology?
The double-sided module can be divided into P-type double-sided and N-type double-sided according to the different crystalline silicon substrates. The currently available mass-produced double-sided battery structure is dominated by P-type PERC double-sided, N-PERT double-sided and HIT.
Comparison of natural advantages and disadvantages of materials
Due to the difference in silicon substrate, N-type double-sided has certain natural advantages over P-type PERC double-sided materials, including high lifetime of oligozoites, no light decay, good low-light performance, good temperature coefficient, high tolerance to metal impurities, etc. .
(1) The lifespan of the minority children is high. Metal impurities are one of the common impurities in semiconductors, and N-type substrates have strong resistance to impurities, and they have a higher tolerance for common metal impurities such as iron and copper. That is to say, under the same metal impurity pollution, N-type substrates The minority carrier lifetime of the silicon wafer is higher than that of the P-type silicon wafer. The high lifespan of the minority children is ultimately beneficial to the output current. Under the same lighting conditions, the converted light energy will be more.
(2) No light-induced attenuation. Conventional P-type batteries use a boron-doped silicon substrate, which is likely to form a boron-oxygen pair after initial illumination, and capture electrons in the substrate to form a recombination center, resulting in 3 to 4% power attenuation. It completely eliminates the light attenuation; the N-type double-sided is different from the PERC double-sided. The substrate is doped with phosphorus, and there is no loss of boron and oxygen to form the composite center, so that the battery has almost no photoinduced attenuation.
(3) The weak light is good. Compared with the P-type single crystal, the N-type single crystal has a more sensitive perception of weak light. In the morning and evening, cloudy or rainy days, the N-type single crystal can capture more light for photoelectric conversion, and the output The battery will also be more.
(4) The temperature coefficient is good. The temperature coefficient is the rate at which the physical properties of the material change with changes in temperature. Compared to the P-type single crystal, the rate at which the open-circuit voltage, short-circuit current, and peak power of the N-type single crystal change with ambient temperature changes is relatively small. High temperature resistance is better, and the power output will be higher under continuous high temperature environment.
Double-sided gain advantage comparison
Compared with the P-type PERC double-sided, the high double-sided coefficient (that is, the ratio of the back electrical parameter to the front electrical parameter under standard test conditions) has become a major advantage for the N-type double-sided to capture market share. N-PERT, HIT double-sided The coefficient can be higher than 90%, IBC is about 80%, and PERC has a low double-sided coefficient. Although some companies say that they can already increase the double-sided coefficient to about 80%, in terms of general mass production technology, PERC double-sided The factor is about 65% to 75%. Taking Yingli, an N-type double-sided representative company, as an example, the mass production of its "Panda" technology has made Yingli the first company in the world to successfully achieve mass production of N-type double-sided batteries.
According to the data of Pucheng Experimental Power Station disclosed by Longji Leye, its 72 double-sided PERC components (power 350W, front power) compared with 60 conventional polycrystalline components (power 280W), 2017.05-2017.06 two months The average power generation gain is 12.04%.
According to the Shanxi Fenyang distributed power station data disclosed by Yingli, its 60 pieces of N-type double-sided modules (power 310W, double-sided power), compared with 60 conventional polycrystalline modules (power 280W), 2017.11-2018.03 The five-month monthly average power generation gain is 17.32%, the highest is 33%.
Yingli N-type double-sided is calculated according to the double-sided power. The module power already includes 11% of the back-side power, and the additional gain on the back side can still reach an average of 17.32%. This further confirms the aforementioned high coefficient of N-type double-sided and low light The conclusions are good performance, good temperature coefficient and no light-induced attenuation.
In the lead-up project of Datong, Yingli's 50MW "Panda" module has always been the leader in power generation. According to statistics in 2017, compared with the neighboring conventional P-type single-sided polycrystalline power station, its monthly power generation is up to 19. 02%; the Datong City Development and Reform Commission announced the operation of the Datong period from January to June this year. It can also be seen that the power generation of Yingli "Panda" modules has performed well as always.
It is reported that in less than two years, Yingli has successively won the double-sided product certifications of the three major institutions of Jianheng, UL, and TüV Rheinland, and is also the only double-sided power generation product in the world that has received all three major certifications.
Comparison of reliability advantages
(1) Mechanical properties. The PERC double-sided process requires laser slotting on the back, which will weaken its own mechanical properties, increase the probability of cracking and debris during the power station application, and seriously affect the reliability of the components; while the current technology of N-type batteries is not useful To the laser and other processes, it will not cause additional damage to the silicon wafer, and the silver paste is brushed on both sides, which improves the stability of the battery.
(2) Reliability under special circumstances. The N-type double-sided has passed the anti-PID test 6 times stricter than the conventional IEC standard test and the damp heat aging test 4 times stricter than the conventional IEC standard test. In terms of anti-PID, anti-humidity performance, has a super ability. In addition, self-cleaning and other characteristics are also the advantages of attracting N-type double-sided technology investors. Especially in areas with high snow cover, when the conventional modules stop generating power due to snow cover, the back of the PANDA BIFACIAL module uses the snow to reflect light to generate electricity, and the heat generated by the power generation accelerates the frontal snow melting rate, and the overall power generation is higher. The picture below is the self-built experimental power station of Yingli. After the heavy snowfall, the N-type double-sided and conventional polycrystalline components are compared with the self-melting snow without any manual treatment.
How does the N-type turn against the wind and emerge toward the sun?
Although N-type double-sided has more material and performance advantages than PERC double-sided, the current mainstream market is still PERC technology. In the final analysis, the price advantage brought by PERC's lower cost. It is understood that the PERC double-sided component only needs to add two processes of depositing a back passivation layer and a back side laser grooving based on the existing production line, with little additional cost. Therefore, in the future, how to achieve effective cost reduction of N-type double-sided technology will become the key to its market competitiveness and competition for market share.
Yu Bo, deputy general manager of Yingli Green Energy, said that N-type double-sided cost reduction can be started from two aspects. On the one hand, the high cost of N-type silicon wafers is one of the main reasons for the higher cost of N-type double-sided wafers. However, in fact, there is no difference in the production cost of N-type silicon wafers and P-type silicon wafers. As a result of higher prices, it is only a matter of time that a scale effect is needed to achieve cost reduction at the silicon end; in addition, silver paste is also a higher cost part of N-type double-sided, and technology such as multi-busbar can be used to reduce silver Pulp consumption, thereby reducing costs.
On the other hand, from the perspective of the enterprise, it is necessary to reduce the cost of N-type double-sided technology through cost reduction and efficiency increase. For example, the company's own production process improvement and optimized process management and control can control the manufacturing cost to a certain extent. ; The introduction of new equipment, new technology superimposed to increase component power, etc. can indirectly reduce production costs.
Today, with PERC as the mainstream, companies are also evaluating the next generation of mainstream technology. At present, whether it is N-PERT, HIT, or TOPCon, N-type double-sided is already the next generation of mainstream technology. Candidate. The proportion of N-type products in the third batch of front-runners has not been greatly improved. If the actual application cases of success among the front-runners may drive the market share of N-type products to increase, accelerate their development to a more mature stage .
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