Professor Sun Yun, Nankai University reminder: SI: environmental issues cannot be ignored

Polaris solar PV net news: consistently in many countries of the world in recent years in the field of photovoltaic research and development strength, low cost, large areas of CIGS (Copper-Indium-Gallium-selenium) battery can already see results. Although its market share is less than 10% of total PV market, but with the CIGS technology breakthrough and the improvement of technology maturity, which will break the single crystalline silicon PV market battery monopoly, with its excellent price-performance ratio becomes a non-homogeneous high-end products will occupy an increasingly large share of the market.

Professor Sun Yun, Nankai University

Reporters: Professor Sun, Hello! Existing pollution in the production process of crystalline silicon cells which link? The current situation? If a technology and equipment are effectively addressed?

Sun Yun: I think the major pollution in silicon and wafer production this aspect, because made of quartz sand of silicon process, requires carbon to produce carbon deoxidation, made of Silicon of purity of more than 97%, relying on its purity 99.7%~99.9% acid pickling. Whether it is chlorine to produce Silicon tetrachloride, Silicon is handled by hydrochloric acid to produce trichlorosilane, goes through distillation, purification, then condensed by hydrogen reduction of high purity polysilicon raw material. Much of this process is carried out at high temperatures. Silicon single crystal ingots or pull in the vacuum condition, higher than the melting point of Silicon 1410 degrees Celsius after a certain amount of time to complete. So the wafer manufacturing process, carbon dioxide emissions, chemical waste disposal, leakage of chlorine-containing gases or liquids, will have varying levels of pollution on the environment. In addition, in silicon chip proliferation of pn junction in more than 900 degrees, so the whole process of amorphous silicon solar cell with high energy consumption, bringing large quantities of greenhouse gas emissions, have to arouse people’s attention, especially the yield, the greater, more important issues. United States gang o and affiliated to the Department of energy national laboratory, Northwestern University research team found that install solar modules made in China and shipped to Europe, its carbon footprint will be in Europe twice for the local manufacture and installation times. Mainly refers to the Chinese standards of environmental protection and the effectiveness of the plant requires less refining and production of amorphous silicon solar cell process requires large amounts of energy, and China used in this process energy is used more fossil fuel than their European counterparts, and low energy efficiency. So the normally high pollution and high energy consumption is above both.

Reporter: amorphous silicon solar cell production collective pollution is still there? Is the industry’s problems, or the problems of enterprises themselves?

Sun Yun: in addition to outside the Silicon raw materials, I think crystal silicon solar cell production and not the entire industry chain has contaminated, such as packaging production almost pollution free, diffusion process of acid and alkali process of cleaning and etching etching, Groove will use some pH stuff, before release, to be dealt with, but also to have greater input than the thin film solar cell to prevent. Thin film solar module cleaning glass or other substrates, and don’t need to acid etch, use small amounts of organic cleaning agent, not only there is no pollution of acid-base and vacuum coating, PV and solar module manufacturing and finished in a workshop, so thin-film battery in this context basically there was no pollution.

I think the pollution of amorphous silicon solar cell industry chain, except for carbon emissions, in order to present technology makes the production process cause pollution are problems of enterprises themselves, mainly to see the alignment is not complete supporting facilities, if implemented fully, coupled with strict management, even though production costs higher, but pollution problems can be avoided.

Reporter: are you as a leader, your specialty is the study of CIGS thin-film batteries. In your opinion, the technology direction for pollution problems?

Sun Yun: so far, we haven’t found CIGS has serious pollution problems. CIGS films by selenization technique after, generally use highly toxic gases hydrogen selenide (H2Se), exhaust gas treatment device, eventually discharge should not be a problem. In addition, most of the CIGS cells, there is a transition layer of cadmium sulfide (CdS) of about 50 nm from the wet process (CBD), its waste liquid which contains small amounts of cadmium (Cd), and after treatment can reach the national standard after discharge. CIGS cell content of Cd in cadmium telluride (CdTe) falls far short of the battery and CdTe cells containing Cd layer around 5~7 μm. CdTe and CdS both of these films are very stable to simulate fire degrees Celsius on the volatile case found no cadmium, solar module packaged well and do not cause pollution. If there is a pollution problem, Germany and the United States would not allow production. At present, overseas have CIGS batteries using cadmium-free transition process, such as Japan of CIGS SolarFrontier battery, no Cd the element, this also reflects the Cd can be removed from the CIGS cells, which is an important direction of the product.

Reporter: CIGS manufacturer in China’s current battery products containing the Cd which ingredients?

Sun Yun: at present, the CIGS production manufacturers such as Hina, place des Vosges and other products containing Cd, no Cd in the country has not seen reports. Because of relatively high conversion efficiency CIGS products containing Cd, higher conversion efficiencies than no Cd 1%-2%. In addition, the CIGS solar module of Cd element in minimal, not as serious as imagined. Especially if manufacturers the ability to damage and failure of solar modules are responsible for recovery of concentrate, people had no need to worry about, of course, to be able to provide the community with no Cd batteries.

Reporter: with amorphous silicon solar cell (module), what are the main advantages of the CIGS thin film solar cell? What are the advantages of better marketing?

Sun Yun: from the battery itself, the advantage is more than the first, low cost and secondly, manufacture process of low energy consumption; and, third, high conversion efficiency of four, good low light response, output power higher than the crystalline silicon solar batteries last, to make a flexible battery with high power density, has a broader application.

We say from a scientific point of view, is the low cost, the current high cost is due to the industrialization of battery technology is still in the incubation period. This product is a cheap glass, stainless steel foil deposited on polyimide substrates or polymer films for solar cells, a few films together around 3~4 μm, very little precious raw material consumption. Crystalline silicon solar cells you will need 200 microns, only this thickness can absorb sunlight and clean. Otherwise, it will be partially absorbed by, affect its efficiency. Silicon ingot slices, zigzag down the Silica fume can no longer be recycled, because it contains a lot of metal components not easily regenerate purification. Each piece you want to cut 300 microns from silicon ingots, the equivalent of one-third Silicon raw material depletion.

Crystalline silicon solar cells from silicon to the commercialization of solar modules, is done by the socialization of industry chain, implementation of specialized mass production, the current product sales price has been reduced to the extreme, profits were assessed by industry chain enterprises. CIGS cells completed within the whole industry chain in a small workshop, and basic raw materials into the plant processed of glass, it’s solar module directly to the PV power plant, each process can be adjusted in the workshop, reducing logistics costs, and component cost control and profit margins are greater.

Low energy consumption in the CIGS solar module production process, too high a temperature will cause the glass to bear. For preparation of light on a polymer substrate of flexible CIGS PV module can only be done at 450 ° c temperature below a short time. Crystalline silicon solar cells from silicon to module, its energy consumption is much higher than thin-film batteries.

SI module conversion efficiency of the laboratory world record world record in 20.5%,CIGS cell conversion efficiency for a long time, the last two years continuously refreshed by enterprises or research institutions, has now reached 21% (Germany Solibro-Hina created). Production line of glass CIGS solar module production efficiency had reached 13%~14%, while mainstream silicon solar module efficiency for PV market 15%~16%, average efficiency of monocrystalline silicon solar module for 16%~17%, judging from the CIGS developments, average efficiencies than amorphous silicon solar cell production line components will be just around the corner.

Due to CIGS thin-film optical absorption coefficients is now the highest of any photovoltaic material, its spectral response for solar cells is also very wide, 1000nm wavelengths still have high quantum efficiency. Test results have shown that in the same place, the same power of PV power plant, energy output than amorphous silicon solar cell 10%. The power station installed at same power prices, the same power plant the benefits of additional 10% and steady decline, indicating that its optical performance and value is outstanding.

I feel, market application aspects, CIGS battery while has low cost, and high conversion efficiency, and anti-radiation capacity strong, and stable not recession, traits, application in distributed station has is good to market competitiveness potential; due to its appearance tones soft elegant, and weak light response good, also very for Yu high-end buildings of BIPV glass curtain wall; on the, stainless steel foil or poly n Asia amine lining late of flexible battery, not only retained has glass lining late battery of excellent performance, and weight light, and can curling folding, and fear fell touch And more suitable for portable mobile power station cut into different size components as required, apply more flexible. Can be embedded in a tent on the roof can also be folded to carry, feel free to open in place for notebook computers, printers, and mobile communication devices; can also be embedded in clothing, in the Sun to charge portable electronic devices. Polyimide substrate CIGS cells, its power to weight ratio up to 1500W/Kg (unpackaged), are unmatched by all current solar cells. In addition to stainless steel foil with CIGS cells have the same application, but also has excellent performance, and is the first choice for some spacecraft. Therefore, the flexible CIGS cells whether they are military or civilian has broad prospects and huge market demand.

Reporter: in your mind CIGS thin-film battery technology improved in the future and how much, there is no technology roadmap?

Sun Yun: CIGS solar cell current laboratory technology matured, major scientific questions to confirm, but require further and finer. The core technology of large area solar module industry has broken, can produce high performance battery pack. Mainly focuses on how to reduce costs in the future, so its price acceptable to the market. I think industrialization is still flawed, copy the expansion has not been reached on the technical level, in Western countries, is unlikely to open such high-end technology to China. Bottleneck lies in the equipment, how to ensure the uniformity of the film (requires multiple uniformity of structure and physical properties of compound semiconductor materials), product yield, stable online monitoring, process control, and reducing the fault rate of the equipment and machine downtime. In particular the manufacture of CIGS thin-film devices is core, but a sample is the subject matter of the technology and equipment has not yet fully mature, you also need to constantly optimize and upgrade. Only the line to copy the expansion shows that CIGS battery technology has achieved real maturity, then FirstSolar CIGS cells will appear. If all the homemade 300 MW output, module average conversion efficiency of 13%, yield is 90%, its battery can cost less than $ 0.5 per peak watt, up GW level production of amorphous silicon solar cell cost.

Reporter: what do you think of CIGS thin film solar cells and amorphous silicon solar cell application?

Sun Yun: amorphous silicon solar cell prices low, high conversion efficiency, monopoly of the photovoltaic market at present, mainly used in various forms of photovoltaic power plants, have an advantage in a large power plant construction on the ground. CIGS cell products there are three forms, namely glass module, stainless steel substrate, flexible solar panel, flexible polyimide substrate modules, each must have a more suitable applications. The flexible battery for conventional crystalline silicon solar batteries cannot be achieved now, is a diversified variety of photovoltaic cells, can play a special role in the field of traditional PV may not cover, can have independent pricing system that does not compete with amorphous silicon solar cell, as people’s awareness of product and applications continues to expand its potential market demand is growing.

Rigid CIGS modules of a glass substrate, with crystalline silicon solar batteries suitable for various forms of photovoltaic power stations. From the appearance of tone and low light-generating capacity, for glass curtain wall with a more prominent advantages, its industrial technologies are currently defective, needs to be perfect expansion to reduce costs. Once the technology is mature expansion, CIGS cells with crystalline silicon solar battery flat, will have a very strong market competitiveness. However, the CIGS module capacity even at hundreds of gigawatts, will not replace crystalline silicon solar photovoltaic market main body of rare precious metal Indium restricts the battery after all infinite, then there may be another Earth-rich raw material manufacture of cheap, efficient batteries replace all battery, become the subject of energy.

At present, the domestic production of amorphous silicon solar cell decay rate the issue has been quite prominent, because of mass production, the blind pursuit of low-cost, so that product quality as before, I suppose next PV market will go there because of the recession and other quality problems caused by a series of disputes, when the time comes people will find CIGS cells stable performance and low decline rates and other advantages, will get more popular.

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