Application of the hottest laser high efficiency p

2022-07-28
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Application of laser efficient processing in the solar energy industry

the rapidly growing photovoltaic industry requires equipment suppliers to provide many solutions, including improving output, yield and reducing cost of ownership. The application of laser plays a more and more important role in these aspects

at first glance, the equipment supply of the solar energy industry is similar to that of the mature microelectronics and display industries. However, the rapid growth and dynamic changes of the solar energy industry present a series of new challenges to all equipment suppliers trying to gain a firm foothold in the supply chain of the solar energy industry. A large number of battery and panel manufacturers have poured into the industry, further aggravating the complexity of the problem. Existing semiconductor equipment suppliers are not familiar with these new manufacturers

although many end-users of solar energy have used laser tools for some time, the relevant processes of laser tools are specific to the solar energy industry and have a very different set of process parameters. In this paper, we review the existing and emerging laser applications, and discuss how and why laser processing will play an increasingly important role in the solar technology route. We also study the new challenges faced by suppliers who are currently engaged in or will soon enter the equipment supply chain

as a variety of solar cell technologies are competing for market share, people are studying various schemes to reduce the cost per watt ($/w) of the final module to consumers. Therefore, equipment suppliers may face very different needs depending on the type of end-users studied (crystalline silicon or thin film). However, we can generally classify these products into some common categories (Figure 1). General end use specific devices are driven by a subset of these categories and are subject to a combination of specific battery technologies and their cost reduction technology blueprints

high efficiency concept

improving the efficiency of solar cells and panels is the most urgent desire of almost every solar manufacturer in the world. Most of the proposed technical blueprints clearly point out that the efficiency of crystalline silicon (c-Si) solar cells will increase by%, and the average value will reach%. For thin-film solar panels, the overall efficiency is low, but it is expected to be improved accordingly. For example, the conversion from single junction amorphous silicon (a-Si) structure to series junction a-si/mc-si (micro amorphous) structure can increase the battery efficiency by about 4% and the overall efficiency of the panel to 10%1 by improving the spectral absorptivity

now c-Si battery manufacturers are most active in pursuing the concept of high-efficiency battery, which is the part that they need to improve repeatedly in their existing product lines and capacity expansion plans. Laser technology will play an important role in the new upper surface and back surface processing stage 2. For example, in metal wrap through (MWT) devices, the thinner metal contact "fingers" are moved to the back. In the emitter wrap through (EWT) device, the power transfer bus is also transferred to the back, so that the upper surface is completely free of metal. This can be achieved by drilling micro through holes to connect the upper surface with the lower surface. With WMT, about 200 through holes need to be drilled for each silicon wafer. EWT requires up to 20000 such through holes on each silicon wafer. Laser drilling is the only process that can possibly meet the speed of commercial scale. At the same time, the laser can also be used to form new structures, such as laser fired contact (LFC), which is necessary to support some advanced thin silicon products

in order to fully meet these different processes, equipment suppliers should integrate lasers with high average power (up to tens of Watts), and can choose to output infrared (IR), visible or ultraviolet (UV) light. They have nanosecond or picosecond pulse properties and excellent beam properties. The M2 parameter is about 1.1 (M2 is about 1.0, representing the theoretically fully focused excitation beam)

"green" equipment

the equipment supply of the current solar production line includes various competitive schemes, some of which use toxic chemicals to produce toxic waste. For example, silk printing and wet etching are widely used in factories. They use the existing complete production line equipment suitable for solar energy production. However, solar energy is an alternative energy and "renewable" energy type, with almost zero carbon emissions. Therefore, there is a strong incentive to adopt green production equipment whenever possible

using DPSS laser for edge isolation is not only more environmentally friendly, but also improves the yield and device efficiency. Especially since crystalline silicon can absorb more light at these shorter wavelengths, the current generation system now relies more on DPSS laser 4 operating in the visible (532 nm) or ultraviolet (355 nm) band. The absorption of 355 nm light wave by silicon is four to five orders of magnitude greater than that of infrared (1064 nm) light wave. Therefore, highly localized upper surface etching can be realized by using q-conversion UV DPSS laser (Fig. 3). In addition to the shallow penetration depth, the ultraviolet wavelength can also obtain a narrow groove at a lower temperature, which can minimize the peripheral temperature damage such as microcracks, which may greatly affect the yield. This enables the trench to be placed close to the edge of the device, reducing the "dead" zone, thereby maximizing the efficiency of the battery

cost of ownership

the manufacturing cost of solar cells and panels is an eternal topic because it has a great impact on the cost $/w delivered to the final solar device. People usually reduce costs by reducing the cost of raw materials or by using production line equipment with the lowest capital expenditure and operating costs

dpss laser provides an ideal solution, mainly due to its low operating cost. In addition, the solar energy industry can immediately benefit from the industrial proven laser design that has been widely used in semiconductor production lines with the speed control system controlling the servo electromechanical rotation. These inherited applications set a corresponding target level for uptime, availability of spare parts, and field service. For example, a high-power laser operating in the ultraviolet band has an output of tens of watts. When operating at full power, the laser will work 24 hours a day, seven days a week for five years. The full load operation cost of this laser is usually USD/hour

yield

although the production of solar cells only requires lower technology and fewer process steps, due to various reasons, the yield of solar cells still lags behind the production of semiconductors, indicating that the material is a homogeneous core material provided according to the requirements of the new national standard issued by the state. These include the problems caused by installing and optimizing new precision equipment and tools in mass production environment, as well as the challenges from maintaining reasonable uptime and trouble free operation. Therefore, automobile technology should be improved as much as possible. In the past, in the solar energy industry, yield optimization plays a secondary role in the long delivery time of equipment and the resulting hasty installation of equipment and production of solar cells to meet market needs. The bottom line is: it is not unusual for the yield level in the solar industry to be lower than 90%. Top suppliers are now announcing that the yield level is greater than 95%. However, it is obvious that the photovoltaic (PV) manufacturing process has not progressed to the yield level required for semiconductor production

there is another aspect that will affect the yield. In the next three to five years, the choice of production equipment will turn to processing thinner and larger silicon wafers. Wafer thickness will soon fall below 200 μ m. The mechanical properties of silicon wafers are more fragile than ever before. Simply put, the contact technology used in these fragile silicon wafers will bear the risk of further reducing the yield level. Therefore, the non-contact nature of laser processing provides a great internal advantage. It is good for reducing the damage rate and microcracks of silicon wafers. Microcracks are one of the main problems leading to unqualified products

production rate

in the past, the reduction of manufacturing costs in the PV industry depended on increasing the production rate of factories, so as to reduce costs through economic scale, which is similar to the phenomenon observed in the microelectronics industry. Over the past decade, each doubling of global manufacturing output has resulted in a 20% reduction in module costs. In this regard, today a high-performance c-Si battery production line can have an hourly output of more than 3000 WPH. The factory generally has several parallel production lines, with a total annual capacity of hundreds of megawatts, and will soon break through the epoch-making gigawatt factory scale. The cost is expected to decrease similarly as the area of the thin film panel increases from Gen 5 to Gen 8 or more

what does this mean for laser process equipment suppliers? In many c-Si laser processes, the output scale of the production line is almost directly consistent with the average laser power level. Therefore, the important driving force here is to increase the average power level by the pulsed DPSS laser while maintaining the characteristics that determine the process yield and operation cost. This includes the quality of the beam, the life of the product and the level of stability between pulses. Figure 4 shows how the power of Q-switched 355 and 532nmdpss lasers has been improved to keep pace with the increasing yield demand

for the production of thin-film panels, DPSS lasers are generally used to form discrete battery isolation and interconnect stripping. In the panel production stage, up to hundreds of thin lines are etched on each deposited film. This etching process is usually referred to as P1, P2 and P3, collectively referred to as the laser pattern structure (Fig. 5). Here, the productivity can not be increased only by increasing the average laser power, but they also need to have the function of highly uniformly etching and sweeping large panels on thin layers of different materials. 6

the limited speed of optical scanning technology means that multiple laser beams must be used at the same time, so the average power requirement is moderate. A more critical requirement is pulse repetition frequency (PRF). When the target scanning rate for a large panel is 2 m/s, the PRF must be very high (up to 100 kHz or even higher) to obtain the desired shell like profile (Fig. 6), while maintaining key features such as short pulse width and excellent repeatability between pulses

equipment compatibility, development time. End users of solar cells and panels now have the option to purchase either complete production lines from some global suppliers or complete production lines configured with different in-line tools. This production line can be highly customized for their solar cell brands. This decision is of great significance to the type and supplier of the equipment used, including the type and supplier of the laser. In addition, the growth rate of solar energy in the past few years, together with the number of new manufacturers entering the market, has brought great demand to the suppliers of complete line manufacturing systems favored by the original solar manufacturers. Therefore, there are reports of long delivery cycle and slow production and development time from time to time

looking into the future, it is very important to recognize that the laser system is the next generation driving tool. With the upgrading of the solar energy industry, this tool should be compatible with future technologies. On the contrary, tools based on modified etching or silk printing equipment types have reached the end of some application lines. This is absolutely true for the processing of thin silicon wafers. The process that needs to be contacted has reached the limit edge of the current production capacity. Therefore, this process cannot meet the requirement that the thickness of silicon wafers is less than 180 μ M technical objective 7. Although the new laser technology can further reduce the cost of the industry and improve the performance of the technical blueprint, the laser itself is not a new thing.

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