ZTERIAL HJT Heterojunction Solar Cell Pastes

在太阳能光伏电池的众多类型中，单晶硅太阳能电池技术已经确立光伏产业显著的优势地位。P型单晶硅发展较早，主流产品经历了PERC电池的不断发展，电池效率已逐渐接近瓶颈。与之相比，N型硅片具有较长的少子寿命、更小的光致衰减，公认未来高效光伏电池发展将切换到HJT、TOPCON等N型电池方向。 

基于N型硅片的异质结电池HJT，结合了薄膜太阳能技术，具备N型硅片低厚度、基本无光致衰减，以及温度系数优良、低温工艺等优点，是已知量产电池中效率最高的结构， 与叠加技术结合，效率提升空间大， 成为了下一代电池技术的最有力竞争者。 

HJT电池组件的综合生产成本相 比PERC电池组件的综合生产成本高约0.17元/W，PERC组件成本约1.26元/W，HJT组件成本 约1.43元/W。

HJT电池的特点与优势  
         1) 结构对称，正背面受光后均可发电，在封装为双面电池后，可获得近10%发电增益。  

         2) 较长的少子寿命，电池的开路电压高， 电池的效率高。  

         3) 温度和光照稳定性好，在弱光和光照升温条件下输出特性几乎无光致衰减。  

         4) 制作工序少，整个工艺通常不超过200℃，硅片本身受热损伤和热型变影响小，可以使用更薄的硅片。  

基于以上特点，HJT电池量产平均效率已突破25％，与传统PERC和TOPCON相比效率明显要高的多，HJT技术的高效率和发电量的长期增益是其天然的优势，目前最大的问题是成本。因此，兼顾提效基础上的降低成本是HJT产业的重中之重。  

HJT的降低成本路线  
         1) HJT采用了与传统晶硅电池工艺设备不兼容的薄膜沉积技术，设备投资高，带来成本的上升。通过推动HJT产业规模化发展，设备成本有望持续下降，并接近PERC水平。  

         2) N型硅片市场价格高于P型，将硅片薄片化可以有效降低电池硅耗量，节约生产成本。  

         3) 银浆的使用是HJT工艺中极为重要的成本组成，采用的HJT银浆需要很好的平衡电阻率、浸润接触，焊接拉力以及印刷性等性能要求。由于HJT双面丝网印刷，银消耗达到烧结型银浆的2倍，往往占电池非硅成本一半以上。 

HJT电池电阻率偏高是其银浆单耗居高不下的最直接原因。在优化银浆体系基础上，通过纳米技术，可以获得更低电阻和银含量的低温银浆。并且，通过印刷图形优化和细栅的进一步细线，可以带来直接的银耗降低。同时，在提效和降本的双重压力下，采用分步印刷工艺等，避开高银耗量的主栅印刷或将主栅和细栅浆料性能分别优化和印刷，降低主栅浆料银含量或引入部分替代银金属，可大幅降低银耗成本。

作为HJT低温光伏电池浆料的先行者，我们推动和优化低温银浆产品的通用化， 并领导了这一进程，开发电阻率极低，适用印刷网板线宽30微米以下, 主栅焊接拉力优良的系列浆料，使用纳米和银包铜技术，大幅降低浆料用量， 可使HJT组件的综合生产成本相比PERC组件的生产成本还低。 随着各种提效和降本工艺技术的持续整合，产业化规模化对性价比提升的有效推动， HJT可望不断发展产业产品优势并转化为市场的主流之一。

Photovoltaics is a fast-growing market; the Compound Annual Growth Rate (CAGR) of cumulative PV installations including off-grid was 34% between the years of 2010-2020. In 2020, North America’s contribution to the total cumulative PV installations amounted to 22%, while Europe 12%, and China accounted for 33%.   

Rising energy demand coupled with governmental efforts to deploy more renewable sources in their energy mix to curb the growing carbon emissions will complement the product demand. Regulators have further offered various fiscal incentives, investment tax credits, and renewable energy grid policies and rebates to promote the use of PV energy.   

The global solar power market size was $180 billion in 2021. The market is expected to reach $200 billion by 2026. In 2020, producers from Asia account for 95% of total c-Si PV module production. China holds the lead with a share of 67%. North America contributed with a share of 2%, Europe with 3%.   

Solar energy is the fastest-growing energy source in the US, and possibly the nation's best hope for achieving its climate goals. A recent report by the US Department of Energy found that solar energy has the potential to power as much as 40% of the nation's electricity by 2035. It is the cheapest and fastest-growing source of clean energy and could produce enough electricity to power all of the homes in the U.S. by 2035 and employ as many as 1.5 million people in the process.

The prices for a typical PV rooftop-system in 1990 have been decreased to about only 10% at the end of 2020. Cost reduction results from economies of scale and technological improvements.    

Among the many types of PV cells, monocrystalline silicon solar cell technology has established a significant advantage in the photovoltaic industry. P-type monocrystalline silicon developed earlier, and the mainstream product PERC cells have experienced the continuous development, raising cell efficiency, which is approaching its theoretical limit. In contrast, N-type silicon HJT cells are recognized as the next-generation cell technology after PERC. The HJT solar cell efficiency has attained 25% in mass production, known as a big breakthrough in power generation with the highest solar cell efficiency for mass production, and much higher potential to improve with the superimposed technology. HJT solar cell is becoming the most powerful competitor of the next generation of solar cell technology.  

The HJT heterojunction technology is currently the solar industry’s best option to increase efficiency and power output to their highest levels. With higher potential gain in efficiency and rather simple processes, HJT becomes an instant hit in the capital market. By far, more than 140 GW of HJT production capacities have been arranged.   

The HJT solar cell is made by sandwiching the N-type crystalline silicon between the thin layers of amorphous silicon. Three important materials are used for HJT heterojunction solar cells: crystalline silicon (c-Si), amorphous silicon (a-Si), and TCO. It uses both crystalline and thin-film technology.   

The all-inclusive production cost of HJT module is about $0.03/W higher than the all-inclusive production cost of PERC module. The cost of PERC module is about $0.20/W, and the cost of HJT module is about $0.23/W.    

Some Major Benefits of HJT Heterojunction Solar Cells Include:   

          1) High solar cell open-circuit voltage and high cell efficiency.    

          2) Less affected by changes in temperature and light.   

          3) HJT cell can produce electricity from both front and back sides once receiving light. Nearly 10% extra power generation gain can be obtained as a double-sided cell.  

          4) Very low annual degradation rate.   

          5) Shorter production process. The whole process usually does not exceed 200°C. The silicon wafer itself is less affected by thermal damage.   

Based on the characteristics above, the average efficiency of HJT solar cell mass production has been significantly higher than the traditional PERC and TOPCON efficiency. HJT solar cell high efficiency and long-term gain of electric generation is its natural advantages. The biggest problem is the cost. Therefore, cost reduction with improving efficiency is a crucial factor for the HJT industry.    

HJT's Cost Reduction Routes   

          1) HJT process uses the technology of thin film deposition that is incompatible with the traditional crystalline silicon PERC cell process equipment. The equipment investment in HJT is high and brings about an increase in cost. As the HJT production capacity and production volume are expected to expand continually in recent years, the equipment cost is expected to continue to decline, close to the cost as PERC.   

          2) The market price of N type silicon wafers is higher than that of P type and thinning the silicon wafer can effectively reduce the silicon consumption of the cells and reduced the production costs.   

          3) The silver paste used in HJT metallization is of a crucial part of the overall cost, which requires a good balance of resistivity, printability and other performance requirements. Due to the nature of HJT double-sided screen printing, silver paste consumption is 2 times that of PERC silver paste, often accounting for more than half of the non-silicon cost of the HJT cells.   

The main reason for the high consumption of the silver paste in HJT cells is the high resistivity. By using molecule-nanotechnology innovation to promote the silver paste system, silver pastes with lower resistivity and lower silver content can be achieved and optimized. In addition, a step-by-step printing process for the busbar and finger line respectively is adopted to avoid high silver consumption of the busbar, plus introduce some alternative silver coated copper pastes which greatly reduce the cost of silver consumption.   

As a pioneer in low-temperature HJT solar cell pastes, we promote and optimize the differentiation and generalization of the HJT metallization process, develop a series of silver pastes with low resistivity for screen printing opening width less than 30 μm, high peel strength, reducing the quantity of the silver paste usage greatly; accomplished by using molecule-nanotechnology and silver-coated copper technology, which can make the all-inclusive HJT mass production cost lower than the mass production cost of PERC.    

With the continuous integration of various improvements and cost reduction process, and the expansion of the mass production, HJT is expected to continue to develop into industrial product advantages and become the one of mainstream of the market. 

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