Cost reducing and efficiency increasing are tireless pursuit of PV practitioners. On silicon wafer side, diamond wire sawing technology has displayed huge advantage. With large scale application of diamond wire sawing technology, mono-Si wafer manufacturing cost greatly decrease. Multi-Si market is also squeezed because of it, and makes multi-Si wafer cost reducing pressure further increase.
However, when multi-Si wafer uses diamond sawing, after regular etching technology, surface reflectance is higher and has obvious stria etc. appearance defects, which severe decreased cell efficiency and prevent diamond wire sawing multi-Si wafer from large scale generalization. In hence, currently, main barrier of diamond wire using in multi-Si wafer sawing lies in matching of cell etching technology.
Under this background, black silicon technology refreshes new vitality again. After regular acid etching, black silicon technology increase a surface etching technology, which solves diamond wire sawing multi-Si wafer’s reflectivity is over high’s problem. As surface reflectivity’s decrease, silicon wafer light absorption capacity increase, which can also attach certain cell efficiency’s increase. In hence, technology of diamond sawing multi-Si matches black silicon technology can both reduce silicon wafer cost but also increase cell efficiency, is the route which multi-Si cell continues improving must be passed.
Currently, diamond wire sawing multi-Si wafer etching main technology routes include black silicon technology and additives direct etching technology. Among, black silicon technology includes dry process and wet process. Comparison of different technology routes are shown as table below.
----Dry process black silicon technology and latest development
Dry process black silicon technology is steady and mature, suede structure is uniformity and efficiency increases the highest. However, it needs to new increase devices and procedures which cost is quite high. Limited by devices’ high capital expenditure, dry process black silicon currently only realized mass production in some first tier cell manufacturers, like JA Solar, Jinko, GCL System Integrated and CECEP etc. It still has continuing development’s market space.
JA Solar is global first enterprise which realized dry process black silicon cell’s large scale mass production. JA Solar high efficiency multi-Si black silicon module RIECIUM cell average transfer efficiency reached 19%, 60pcs black silicon cell module power concentrates upon 270W. Jinko launched multi-Si Eagle Black series module, dry process diamond wire sawing black silicon product, in Q1, 2016, black silicon cell average efficiency reached 19.2%, 60pcs and 72pcs cell module maximum output power reached 280W and 330W, respectively; Nov 2016, CECEP (Zhenjiang) announced that, its high efficiency multi-Si cell which used PERC + RIE black silicon technology, realized mass production, average transfer efficiency broke through 20% and multi-Si module power exceeded 285W.
Apr 2017, dry process black silicon device manufacturer Belight Technology released 4th generation RIE dry process black silicon mass production device Tysol-4000. Capacity of this device could reach 4000pcs/h, mass product CoO cost was around CNY 0.1/pc, device activation reached 98% and cell mass production efficiency could increase more than 0.6% in average. It is reported that, Belight Technology dry process black silicon device shipment has exceeded 1GW.
Aug 2017, dry process black silicon multi-Si PERC cell, which independently R&D by GCL System Integrated, average mass production efficiency exceeded 20.3% and highest efficiency reached 20.8%. GCL will drive on higher aim, which is mass production average efficiency exceeds 20.5% and highest efficiency 20.8-21%, this year, continuously breaking through and challenge the limit.
----Wet process black silicon technology and latest development
Compare with dry process black silicon technology, wet process black silicon technology new increase cost expenditure is relatively small, and can realize 0.3-0.5%’s efficiency increase. However, this technology uses slot technology, which compatibility with current chain technology is poor, and it needs to face problems of treatment of waste acid which contains silver and local government environmental protection management and control. Wet process black silicon technology’s symbolize enterprises are Canadian Solar, GCL Poly, BYD and Sumec etc.
Canadian Solar started wet process black silicon technology project investigation and project establishment since 2009. In 2014, it successfully extended this technology to production line, realized industrialization of wet process black silicon technology first in the world. Currently, Canadian Solar mass production black silicon cell average efficiency exceeds 19%, which efficiency is 0.45% increased compare with regular multi-Si cell. Black silicon module output power increases 4W. At the end of 2017, Canadian Solar will have 4GW wet process black silicon capacity.
Jul 2016, Sumec Inc. announced that, it joint contributed and founded JV Xuzhou Zhonghui PV Technology with Jiangsu Solarspace Co. Ltd. and joint developed wet process black silicon technology. In 2017, ‘A kind of multi-Si surface inverted pyramid structure and its preparation method’, which is independently R&D by Sumec Phono Solar, got invention patent. This multi-Si inverted pyramid light trapping structure can decrease surface recombination and make solar cell have higher efficiency. Besides, Sumec Phono Solar plans to launch composite high performance PV module which is based on ‘black silicon + MWT’ in the year.
Feb 2017, GCL System Integrated multi-Si wet process black silicon PERC cell started mass production. Wet process black silicon PERC cell average efficiency has reached 20% and unit pc highest efficiency reaches 20.5%. On black silicon technology industrialization route, GCL System Integrated executes cell and module products routes of multi-heads advance together. In 2017, it will have 1.2GW black silicon cell go into fully operation.
Mar 2017, CECEP signed cooperation development agreement with Germany RCT PV Technology on wet process black silicon technology. Both parties reached cooperation on joint developing wet process black silicon industrialization technology on RCT devices. Via cooperation, they can carry forward industrialization process quicker and further realize cost decrease and efficiency increase.
Except cell enterprises, silicon wafer enterprises also active distribute and lead in black silicon technology in order to accelerate pushing forward generalization and application of diamond wire sawing multi-Si. GCL Poly released TS series wet process black silicon wafer in Nov 2016. The black silicon chip surface is uniformity and owns ‘perfect’ appearance. On cell side, it can realize around 0.3-0.4% efficiency gains. GCL Poly stated that, it is willing to free sharing this technical proposal with downstream cell clients. Up to end of Jul 2017, GCL Poly has sold more than 13M pcs black silicon wafer. By the end of 2017, its Yangzhou 2GW black silicon base will operation according to the plan.
----Additive direct etching technology and latest development
Compare with black silicon technology, biggest advantages of additive direct etching technology is process is simple and hardly needs extra cost expenditure. However, this technology will cause appearance crystal flower problem, reflectivity after etching is still high and cell efficiency does not increase, even may have efficiency loss. In hence, this technology needs further increase. As additive direct etching technology is easy to realize large scale mass production, matching diamond wire sawing multi-Si wafer, it can reduce production cost, which is benefit for promoting application of diamond wire sawing multi-Si wafer. In hence, this technology has large scale application in 2017.
It can be seen that, above three methods have their advantages and disadvantages. Specific option still needs market’s further verification. View from current industry progress, each method is at the stage of mutual development. ASIACHEM believes that, wet process black silicon technology with relatively low investment cost, can solve diamond wire multi-Si etching problem quite well, can effectively increase cell efficiency and module output power, and make wet process black silicon technology have quite big market potential. With wet process technology and device’s continuous improvement, this technology is expected to realize rapid development in 2018.
ASIACHEM believes that, continuous improvement and perfection of black silicon will lay a solid foundation for diamond wire sawing multi-Si wafer’s leading in and cost’s decreasing. Under situation of mono-Si market share continues increasing, application of diamond wire sawing multi-Si wafer matching black silicon technology is the route which multi-Si cell continues improving must be passed. In the future, black silicon technology is expected to become mainstream technology route to realize high efficiency multi-Si mass production.