SEALED BATTERY

SEALED BATTERY

A valve-regulated lead-acid battery (VRLA battery) is sometimes called sealed lead-acid (SLA), gel cell, or maintenance free battery. Due to their construction, the gel and absorbent glass mat (AGM) types of VRLA can be mounted in any orientation, and do not require constant maintenance.

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Battery ProfileSunbright Power, leading manufacturer focused in design and produce maintenance free sealed lead acid battery in China. The company registered capital of 8 million USD, with a total investment 70 million USD. It covers an area of 220 acres, 70,000 square meter production plant, and annual production capacity of one million KVAh. The batteries made by Sunbright include backup batteries applied in telecommunications, Power Plant, UPS battery, fire alarm system, emergency lighting and efficient energy storage batteries used in solar energy, wind energy and, as well as motive power batteries for electric vehicles, golf carts, electric forklift, electric traction trucks and other fields. All products are CE certificated, UL certificated, and TLC, ROSH certificated. SBB has won good reputation from market. In the year 2008, SBB is the only power supplier for Mount Everest section of Olympic torch route.

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Assembling Buildings in-Production Test-Research-Center

It has been proved that when the type I layer approaches the A - Si: H / PC - Si: H transition state, the type I layer contains a large amount of amorphous phase, but still in the microcrystalline phase range, the conversion efficiency of the single-junction microcrystalline silicon thin film solar cell reaches the maximum [ 23 " 85 ].In such a deposition range, the open circuit voltage Va increases significantly with the increase of silane concentration Sc [ 8' 84 ].This phenomenon is attributed to the change in crystallinity of the type I layer. It has been observed that there is a linear relationship with Raman crystallinity in P - I - N and N - I - P devices [?]。The single junction microcrystalline silicon thin film solar cell can reach 530550 mV.Also, the research team reported a record close to 600 mV, and the quantum efficiency curve showed microcrystalline phase characteristics [ 23 ].
In theory, recombination in type I layer is the decisive factor of VOE.Measuring the composite center density of type I layer in the fully operational state of the device is a big challenge, but the recently developed Fourier transform photo-generated current spectroscopy FTPS technology can measure defect - related absorption in type I layer.In the experiment, solar SEALED BATTERY are used as external photodetectors, and the absorption spectrum of solar SEALED BATTERY can be obtained by calibrating the internal detectors of FTPS spectrometer [ 56' 57 ].FTPS technology can measure the absorption coefficient of type I layer whose photon energy is far less than the band gap range.In microcrystalline silicon thin-film solar SEALED BATTERY, the absorption coefficient of photon energy of 0.8 eV can be used as the estimate of the density of suspended bond recombination centers [ 57 ].
The main reason why high VOE can be obtained near A - Si: H / MC - Si: H transition state is the passivation effect of amorphous materials on grain boundaries and interfaces.Because the FTPS technology estimates the absorption coefficient of 0.8 eV as the composite center density of the type I layer, the smaller the FTPS signal, the larger it is as shown in the actual .15.In principle, microcrystalline silicon thin film solar SEALED BATTERY should be close to crystalline silicon solar SEALED BATTERY ( about 700 mV ), but this is not practical in practice because microcrystalline silicon MC - Si: H material has higher defect density and higher recombination loss.Even after good passivation, PR - Si: H still has many grain boundaries, and the built-in electric field ( BUILT - INELETCHELD ) that helps carrier drift collection is sharply reduced in the near open state, causing greater recombination losses and limiting KE.
The most advanced single junction microcrystalline silicon thin film solar cell has a fill factor ff - like of about 70 %, laboratory records show that ff reaches 77, and it has also been reported that very thin type I layers get > 70 % ff [ 23 ].On the other hand, technical problems such as shunt resistance can easily reduce ff to > 60 %, which will become a major problem in the process of preparing microcrystalline silicon thin film solar SEALED BATTERY.
Among the various electrical parameters of the microcrystalline silicon thin film solar cell, it is reported that if the thickness of the type 1 layer is determined, the silane concentration sc is almost constant in the range of MC - si: h, but will suddenly decrease in the transition to a - si: h [ 23' 87 ].It has been reported that the highest JSC value is 30mA / cm2 and most published JSC values are 2025 mA / cm2 [ 23.69 ].In order to obtain reliable values, it is necessary to design a reasonable structure for microcrystalline silicon thin film solar SEALED BATTERY to prevent lateral collection.AM 1.5 spectra also need to be accurately calibrated to measure volt-ampere characteristic curves / and to determine the person's position.In addition to these technical factors, which will affect the uncertainty of AC reported values, they also depend on the thickness of type I layer [ 23 ] and optical optimization ( see section 4.3.1 ), which are quite different in different laboratories.On the other hand, reasonable optical optimization can effectively improve J *, thus improving the conversion efficiency of microcrystalline silicon thin film solar SEALED BATTERY._ At the early stage of research and development, the type I layer of single junction microcrystalline silicon thin film solar cell was highly crystallized, and the deposited parts were far away from the 3 - Si: H / MC - Si: H transition state.Under such conditions, the microcrystalline silicon thin film solar cell has no photo-induced attenuation | 6' 91. In recent studies, the crystallinity of the type I layer changes and the deposition conditions are close to the A - Si: H / F - Si: H transition state, then the microcrystalline silicon thin film solar cell exposed to AM 1.5 spectrum will show moderate photo-induced attenuation. On the other hand, the microcrystalline silicon thin film solar cell is completely stable when exposed to red light [ 94 ].These studies show that microcrystalline silicon thin film solar SEALED BATTERY with low crystallinity have a strong photo-induced attenuation effect, which means that the observed photo-induced attenuation may be caused by the amorphous phase in MC - Si: H layer [ 92' 94 ].After 1000 h of 100 MW / cm2, AML. 5, 50 c photoaging treatment, a typical 2pm thick microcrystalline silicon thin film solar cell deposited in the 3 _ si: h / MC - si: h transition state will show a 5 % 10 % reduction in relative conversion efficiency [ 93 ].Such attenuation is mainly represented by a decrease in FF, followed by a decrease in FF.Attenuation of performance of microcrystalline silicon thin film solar SEALED BATTERY is accompanied by an increase in defect-related light absorption ( about twice as much as measured by FTPS method ).Even if the I - type layer with higher crystallinity has stable performance, its defect-related light absorption is higher than that of the photo-attenuated sample deposited near the A - Si: H / PC - Si: H transition state.
The photoinduced attenuation of MC - Si: H suggests some future theoretical research directions:
The exact mechanism of photoinduced attenuation needs to be clarified.
In addition to the crystallinity of the type I layer, it is necessary to identify other factors that contribute to the photo-induced attenuation effect.
it is worth note that.In non - microcrystalline laminated SEALED BATTERY, even if the photo-induced attenuation effect of the bottom cell can be observed, it is not obvious, because most high-energy photons will be absorbed by the A - Si: H top cell.
In order to obtain a sufficiently high external quantum efficiency for microcrystalline silicon thin film solar SEALED BATTERY in the long wavelength band, a necessary condition is a sufficiently low contamination level, because contamination will become a dopant for the type I layer.Any contaminated dopant will reduce the built-in electric field, which is responsible for collecting carriers within the thickness of the type I layer, so contamination will eventually reduce the quantum efficiency of the entire wavelength range [ 95 ].Through the side walls of the raw gas and the reaction chamber, O atoms can easily mix with the active layer deposited by human plasma [ 96 ].O can become a donor in Si, thus reducing the built-in electric field in the entire I - type layer, which will affect the external quantum efficiency curve, especially the long wavelength band of the spectrum.In the P - I - N type upper layer configuration, B is used to dope the first deposited P type layer, so B may contaminate the initial part of the I type layer, especially TW when the deposition temperature is higher than 200 C, or deposit subsequent thin films directly in the same reaction chamber without further preventive measures.B pollution will affect the quantum efficiency curve in the short wavelength region and limit the sum ff.
non - microcrystalline laminated SEALED BATTERY
In order to fundamentally improve the conversion efficiency of low-temperature deposited thin film solar SEALED BATTERY, it is an important method to stack several SEALED BATTERY with different optical band gaps using a stacked double-junction or triple-junction structure.Conceptually, the advantages of this stacking technique are:
Combining different band gap materials can make more effective use of human light.Higher open circuit voltage can be obtained, while lower current density will reduce the problem of series resistance.Using thinner A - Si: H top SEALED BATTERY can reduce the photoinduced attenuation effect.
Since the 1980s, people have begun to study multi-junction stacked SEALED BATTERY with amorphous silicon a - si: h and hydrogenated amorphous silicon germanium a - sige: h as photogenerating layers, and now several companies have realized relevant commercial production ( see chapter 5 ).However, this technology will encounter two problems:
It is difficult to fabricate a high-quality device-level A - SiGe: H intrinsic layer with a band gap of less than 1.5 eV.Ge H4 source gas cost is relatively high.
After that, microcrystalline silicon PTC - Si: H with a low band gap of 1.1 eV was introduced as an effective photogenerating layer, and a - Si: H / JNC - Si: H laminated cell called non - microcrystalline laminated cell 1' " 0 - 1 was designed. In Japan, a novel laminated cell concept called mixed cell C69 ] O became a new research direction, thus promising to develop a thin film solar cell with high conversion efficiency and low cost.
The earliest industrialized non - microcrystalline laminated SEALED BATTERY pack was a hybrid SEALED BATTERY pack introduced by Japanese Zhong Yuan.This hybrid SEALED BATTERY module with a stable conversion efficiency of more than 8 % is sold in Japan's domestic market.For the purpose of testing, Zhong Yuan also prepared a 0.41m2 large area module with an average conversion efficiency of 11 % in the initial state and a maximum initial conversion efficiency of 12.5 % confirmed.
In fact, the band gap combination of 1.1 eV and 1.75 eV can be proved to be very close to the ideal stacked cell design by basic theory [ 71 ].If we assume that all human-emitted photons with energy greater than the band gap can be absorbed by the top cell and the bottom cell, according to the calculation of the filling factor ff and the open-circuit voltage of the band gap and p - I - n type structure [ 72 ], we can get the half-theoretical and half-empirical conversion efficiency limit, and prove that the ideal band gap combination is 11ev for the bottom cell and 1.75 ev for the top cell.
On the other hand, the photogenerated layer thickness ( I - layer thickness ) of the top cell and the bottom cell needs to be reasonably designed to obtain the same photogenerated current and meet the current matching requirements of the current continuity law.Because it is an indirect band gap semiconductor material, the energy is slightly higher than the absorption coefficient of the band gap.
The typical structure of such a non - microcrystalline laminated cell still cannot absorb all human photons with energy larger than the band gap most effectively, because only a relatively thin absorption layer can be used, the S - W effect ( photo - attenuation effect ) limits the thickness of the A - Si: H top cell to about 0.25 / XM, while the deposition time and relatively high preparation cost limit the thickness of the / / C - Si: H bottom cell to 12 / XM.Due to these limitations, the stable conversion efficiency of the small-area non - microcrystalline laminated structure test cell is now 11 % 12 %.The volt-ampere characteristic curve [ 1 1 ] and the external quantum efficiency curve given by the non-microcrystalline laminated SEALED BATTERY prepared by our laboratory at the University of New Chastel in Switzerland are as shown in the actual .20.If we compare the non - microcrystal stacked SEALED BATTERY before and after the photo-induced attenuation effect, the conversion efficiency 7 decreases from the initial 12.3 % to a stable 10.8 %, but the open-circuit voltage remains at I.4V ..In such a non - microcrystalline stacked configuration, the attenuation is limited to the S - W effect of the A - Si: H top cell, even though the deposited type I layer is close to A - Si:
In the transition state, the bottom SEALED BATTERY also showed no attenuation.Up to now, no research team has observed the photo-induced attenuation effect of non - microcrystalline laminated ME - Si: H base SEALED BATTERY.The possible reason is that the bottom cell is not exposed to the entire AM 1.5 spectrum and can only receive the red and infrared light spectrum transmitted through the A - Si: H top cell.
Even if the bottom cell does not undergo photoinduced attenuation, the currently reported non - microcrystalline laminated cell still has a huge difference between the initial conversion efficiency ( more than 14 % ) and the stable conversion efficiency ( 11 % 12 % ).There are two ways to reduce the photo-induced attenuation effect of non-microcrystalline laminated SEALED BATTERY:
Limiting stack of base SEALED BATTERY: In the designed non-microcrystalline stack, the short-circuit current density of PC - Si: H base SEALED BATTERY is lower than that of A - S: H top SEALED BATTERY, so that the characteristics of the stacked SEALED BATTERY are determined by the restricted base SEALED BATTERY and the stack is more stable, but such non-microcrystalline stack SEALED BATTERY have relatively high temperature coefficients and will lose considerable conversion efficiency at higher operating temperatures.
Very thin A - Si: H top SEALED BATTERY: If the I - layer of A - Si: H top SEALED BATTERY is reduced to 0.2 mm, the top SEALED BATTERY will have little attenuation and a lower temperature coefficient, with little loss of conversion efficiency at higher operating temperatures [ 27 \ however, in the simple stacked configuration shown in actual. 19, very thin A - Si: H top SEALED BATTERY can only provide a small short-circuit current density, severely limiting the stacked structure design.This is because the configuration is too simple and the A - Si: H top SEALED BATTERY does not have an effective light trapping structure.For this reason, our research team at the University of New Chastel has attracted zinc oxide intermediate reflector ( ZIR ) [ 102 ] between the top SEALED BATTERY and the bottom SEALED BATTERY.
The preparation of non-microcrystal laminated batteries with ZIR is often more complicated in laboratory or large-scale production, but represents an important technical route to further improve the stable conversion efficiency of non-microcrystal laminated batteries.In ZIR technology, light reflection through the A - A: H / ZnO interface can increase the current of the top cell without increasing the thickness of the A - Si: H top cell and still maintaining the device stability of the top cell, thereby increasing the total current of the non - microcrystalline stack.
Through the ZIR structure, our research team at the University of New Chastel has achieved a stable conversion efficiency of 10.8 % for laboratory samples using a similar structure. Japanese Zhong Yuan prepared a non-microcrystal laminated SEALED BATTERY laboratory sample with an initial conversion efficiency of 14.7 % based on the measured light absorption data of A - Si: H and - Si: H thin films, assuming that the transparent conductive oxide TCO and doped layer have smaller light absorption and the back mirror is ideal, Monte Carlo simulation calculated the optical characteristics and photogenerated current of the non-microcrystal laminated SEALED BATTERY with ZIR and predicted a stable conversion efficiency of 15 %.A recent numerical simulation based on the real light absorption data of ZnO and doped layers gives a stable short-circuit current density of 14mA / cm2, which is equivalent to a stable conversion efficiency of 13 % and 14 %.
Summary
Microcrystalline silicon Si: H materials have only recently been used in the photogeneration layer of silicon-based thin film solar SEALED BATTERY' The high conversion efficiency devices prepared by MC - Si: H are an important research direction of thin film solar SEALED BATTERY.The deposition equipment of MC - Si: H and A _ Si: H are plasma enhanced chemical vapor deposition PECVD, and the source gas is a mixture of SiH4 and H2, but the preparation of Si: H requires a lower silane concentration SC.Microcrystalline silicon thin film solar SEALED BATTERY have the advantages of non-toxic raw materials, low-temperature deposition and more convenient large-area preparation, and have great potential to reduce the cost of photovoltaic modules.
MC - Si: H is a complex material, containing many nanocrystalline silicon embedded with A - Si: H groups.It is easier to dope than A - Si: H and more sensitive to pollution.The nucleation and growth of FIC - Si: H determines the device quality. A certain amount of microcrystalline phase is needed to passivate nanocrystalline silicon and reduce defect-related light absorption, which requires reducing H concentration and increasing SC, thus approaching the A - Si: H / MC - Si: H transition state.Increasing the volume fraction of amorphous phase in the type I layer of microcrystalline silicon thin film solar cell can indeed increase the open-circuit voltage Voe.
The optical properties of MC - si: h are very different from a - &: h.Si: h has an indirect optical band gap of 1.1 ev, so the absorption coefficient for higher energy photons ( av > l 1 ev ) is relatively low.However, the direct band gap of A - Si: H is about 1.75 eV, which has a large absorption coefficient for photons with energy greater than the band gap ( AV > 1.75 eV ).On the other hand, the absorption spectrum of # - Si: H shows that the material has certain amorphous phase characteristics such as Ulbach tail state and defect-related light absorption at 0.8 eV for photons with energy lower than the band gap, while the absorption spectrum of monocrystalline silicon does not have these characteristics.Fourier Transform Photogenerated Current Spectroscopy ( FTPS ) can measure these optical properties to determine the material properties of these photovoltaic applications.
The coplanar electron transport characteristics of MC - Si: H are very similar to those of A - Si: H, which can be understood as the electron transport is limited by the amorphous phase of the material.Due to the limitation of electron transport characteristics and the corresponding short diffusion length, microcrystalline silicon thin film solar SEALED BATTERY generally adopt P - I - N or N - I - P device structures, so the increased drift of the built-in electric field in the I - layer is the main mechanism of carrier collection.At present, the conversion efficiency of the most advanced single junction microcrystalline silicon thin film solar cell is about 10 %.Microcrystalline silicon thin film solar SEALED BATTERY exhibit moderate photo-induced attenuation and depend on the volume fraction of amorphous phase and the formation of attenuated irradiation spectra.In order to further improve the conversion efficiency of single junction microcrystalline silicon thin film solar SEALED BATTERY, the short-circuit current density can be correspondingly increased by improving the light trapping structure.The development of a better new transparent conductive oxide TCO or structured substrate ( periodic grating or irregular metal mirror ) can effectively enhance the light trapping structure.These areas are the focus of current research.
The most important type of silicon-based thin-film solar SEALED BATTERY developed at present is non-microcrystalline laminated SEALED BATTERY, with the structure of a - si: h top SEALED BATTERY and MC - si: h bottom SEALED BATTERY stacked.It can be theoretically proved that this material combination has an optimum band gap combination of top and bottom SEALED BATTERY very close to AM 1.5 spectral optimization conversion efficiency.The initial conversion efficiency of the non - microcrystalline laminated SEALED BATTERY was recorded as 14.7 %.In order to reach the maximum conversion efficiency, a zinc oxide intermediate mirror ZIR can be used between the top cell and the bottom cell, and the A - Si: H top cell of this non-microcrystalline laminated cell is affected by less photoinduced attenuation effect.Because it is only exposed to the long wavelength band of the solar spectrum, the ME - Si: H base cell is relatively stable.In order to achieve high conversion efficiency and device stability at the same time, it is necessary to reduce the thickness of the A - Si: H top cell and further optimize the light trapping structure, thus hopefully achieving a stable conversion efficiency of 13 % and 14 %.Japan's Zhong Yuan has already started commercial production of non-microcrystalline laminated SEALED BATTERY modules, while several other companies ( mainly Japanese companies ) are also doing corresponding research and development, and some of them have developed sample modules. Silicon - based thin-film solar SEALED BATTERY have better aesthetic appearance and diversity of substrate material selection, and are very suitable for BIPV application.On the other hand, the concept of non - microcrystalline laminated SEALED BATTERY can achieve 10 % stable component conversion efficiency.These advantages can convince people that the commercial large-scale production of non-microcrystalline laminated SEALED BATTERY modules will effectively reduce the cost of solar SEALED BATTERY modules in the next few years, thus achieving affordable access to the Internet.
amorphous silicon thin film solar cell
Mirozeman Introduction to 5.1 of Delft University of Technology in Holland
In, the first report on amorphous silicon layer was made, and the film deposited by RF glow discharge was called " silicon from silicon" [ 1 ].Ten years later, Walters Pear and Peterlecomber in university of dundee reported the semiconductor properties of amorphous silicon, confirming that adding PH3 or pressure gas to the glow discharge mixture can increase the conductivity of amorphous silicon by several orders of magnitude [ 2 ].This discovery is of far-reaching significance because before this, it was generally believed that amorphous silicon could not be doped into N - type semiconductors or P - type semiconductors by substitution.At that time, people did not immediately realize that H would play an important role in doping amorphous silicon thin films.In fact, doped amorphous silicon suitable for microelectronic applications requires an alloy of Si and H, so electronic grade amorphous silicon is often called hydrogenated amorphous silicon A - Si: H ..
The successful doping of amorphous silicon has aroused great interest in this material for the following reasons:
A - Si: H has several good characteristics and has created many new fields for the application of semiconductor devices.In the visible band of the solar spectrum, A - Si: H has a higher absorption coefficient, and a 1 - thick A - Si: H film is enough to absorb 90 % of the available solar energy.
Glow discharge deposition technology is now called plasma enhanced chemical vapor deposition PECVD, which can deposit a large area of a - si: h thin film larger than 1m2 at a low temperature of 100400 c.The lower process temperature allows the use of more kinds of low-cost substrates, such as glass plates, metal sheets or polymer sheets.
A - Si: H can be simply doped to form an alloy by adding a suitable gas to SiH4 source gas.
These characteristics make A - Si: H an ideal material for low-cost thin-film solar SEALED BATTERY.At present, in addition to photovoltaic applications, A - Si: H is also used for thin film transistor TFT of flat panel display and photoconductive layer of electrophotography.
Since 1976, Carlson and W Ronski have successfully prepared an amorphous silicon thin film solar cell [ 3 ] with a conversion efficiency of 2.4 %, the amorphous silicon thin film solar cell technology has made great progress and now has achieved an initial conversion efficiency of 15 %.At present, amorphous silicon thin-film solar SEALED BATTERY have become mature commercial thin-film solar SEALED BATTERY, reaching a component shipment RA of 25.8 MWP in 2003.
Development of Amorphous Silicon Thin Film Solar Cells
In the 1970s
In 1976, Carlson and W Ronski of RCA Laboratories in the United States announced the successful preparation of the first amorphous silicon thin film solar cell [ 3 ].This single junction P - I - N amorphous silicon thin film solar cell was deposited on a glass substrate coated with transparent conductive films TCO and A1 back contact, achieving a conversion efficiency of 2.4 %.In order to increase the output voltage of amorphous silicon thin film solar SEALED BATTERY, a multi-junction cell with stacking concept is introduced [ 6 ].The key progress in industrial production is the monolithic integrated amorphous silicon thin film solar cell [ 7 ].The required output voltage can be simply obtained from a single substrate by using the monolithic series integration of subSEALED BATTERY.In 1980, the monolithic amorphous silicon thin film solar cell was commercialized by Japan's sanyo motor and fuji motor and applied in the field of electronic consumer goods such as hand-held calculators and electronic watches.
In the 1980s
In the 1980s, many researches on amorphous silicon thin film solar SEALED BATTERY focused on the development and optimization of A - Si: H based alloys.People combine p - type hydrogenated amorphous silicon carbon a - sic: h as the window layer [ 8 ] with lower light absorption, while hydrogenated amorphous silicon germanium a - sige: h is used as the low band gap layer 1 of stacked laminated SEALED BATTERY, and the substrate with surface texture is attracted to increase light absorption [ 1 3.Laboratory batteries achieved an initial conversion efficiency of 11 % and 12 %.In the late 1980s, amorphous silicon solar SEALED BATTERY entered the market as the next generation of solar cell components, with the application goal of low-cost off-grid power generation system O these components are single junction P - I - N amorphous silicon thin film solar SEALED BATTERY, and the production method is mainly single cavity batch process.The typical area of the module is 0.10.3m2, the stable conversion efficiency is up to 5 %, and the output power is about 14W.However, this promising thin-film solar cell technology has encountered some quality problems, such as photo-induced attenuation at the initial stage of installation, and corrosion of contact electrodes due to insufficient frame-mounting protection of components. These problems, which are still difficult to solve, have caused a temporary setback for the further commercialization of amorphous silicon thin-film solar SEALED BATTERY.
In the 1990s
In the 1990s, the main research and development direction was to realize components with stable conversion efficiency of 10 % and high process production rate.U.S. BP Solar [ 11 ], Japan Sanyo Motor [ 12 ] and Fuji Motor [ 10 ] optimized hydrogenated amorphous silicon germanium A - SiGe: H alloy laminated SEALED BATTERY, while U.S. Uni - Solar realized the structure M of triple junction SEALED BATTERY.The development of amorphous silicon thin film solar SEALED BATTERY in the 1990s was characterized by a multi-junction cell structure and improved assembly framing.Department of Organic Materials?The lightweight frame prepared by J replaces the aluminum frame, reduces the corrosion problem of the contact electrode, provides better protection for the assembly, and ensures the output power to be extended to 20 years.The stable conversion efficiency of the module area up to 1 module total area is increased to 6 % 7 %.By the end of the 20th century, the annual capacity of single-junction and multi-junction amorphous silicon thin-film solar cell modules worldwide will reach about 30 MWP.The application of modules has moved from off-grid power generation to BIPV integration.
At this stage, the microcrystalline silicon # I junction amorphous silicon thin film solar cell' % j' deposited by low temperature plasma enhanced chemical vapor deposition PECVD technology
Materials.In 1994, the University of New Chastel in Switzerland introduced non-microcrystalline laminated batteries, combining A - SL: H top-voltage batteries and Si: H bottom batteries [ 15 ].The great potential of the concept of non-microcrystal laminated SEALED BATTERY quickly shows the 11 % 12 % stable conversion efficiency of the corresponding triple junction SEALED BATTERY [ 16 ], while Japanese Zhong Yuan started the commercial production of non-microcrystal laminated SEALED BATTERY, so the research focus of non-microcrystal laminated SEALED BATTERY with - Si: H shifted from improving conversion efficiency to increasing deposition rate.Several new deposition technologies, such as VHF - PECVD, HW CVD and ETP CVD, have been studied and developed, and the absorption layer film has been prepared at a high deposition rate of 1020 A / s.
Years later
Since 2000, the research has focused more on understanding and optimizing the light trapping structure, especially the surface texturing and the new transparent conductive oxide TCO material.New deposition technologies have been developed commercially to make ZnO as a substitute for S NO2 ( 3 materials M' 2' \ several deposition equipment manufacturers have started to develop commercial production equipment to produce silicon-based thin film solar SEALED BATTERY on a large scale [ 21' 223 ].At present, the most advanced amorphous silicon thin-film solar cell production line has fully automated equipment, which can realize large-area deposition of more than 1m2, with an annual capacity in the range of 1030 mwp, Mitsubishi heavy industry of Japan of 10 mwp, zhong yuan of 20 mwp and uni - solar of the United States of America of 30 mwpo 5.2.5. in order to improve performance, reduce costs and increase competitiveness in the photovoltaic market, amorphous silicon thin-film solar SEALED BATTERY currently have several key research and development directions:
To improve the conversion efficiency of amorphous silicon thin film solar energy: the conversion efficiency is the most important performance parameter of the solar cell. To improve the conversion efficiency of amorphous silicon thin film solar cell, it is especially necessary to increase its current density T23. Therefore, optical optimization should be further developed to improve the light trapping structure and reduce the light absorption loss.In the upper layer configuration, a thin film is deposited on a glass plate substrate, and it is necessary to develop a transparent conductive oxide TCO front contact material.Optimize the surface morphology and improve the light trapping effect.In the substrate configuration, the opaque carrier may be rigid or flexible, requiring improved back contact texturing and reflectivity.It is also necessary to further optimize the photoelectric quality of each layer of thin film, such as: amorphous silicon a - si: h absorption layer, hydrogenated amorphous silicon germanium a - & ge: h absorption layer, doped layer, doped layer and intrinsic layer interface.
Reducing the influence of the photo-induced attenuation effect: the photo-induced attenuation effect, also known as S - W effect, will reduce the initial conversion efficiency of amorphous silicon thin film solar SEALED BATTERY by 15 % 30 %.If we can fully understand the mechanism of S - W effect, it will help to improve the stability of amorphous silicon thin film solar SEALED BATTERY under illumination.The use of a thinner absorption layer can reduce the effect of photo-induced attenuation to some extent, but the use of a thinner absorption layer relies heavily on an effective light trapping structure to ensure adequate light absorption.
Increasing the deposition rate of the absorption layer: in order to reduce the investment cost of the amorphous silicon thin film solar cell deposition equipment and thus the component cost, it is necessary to make the deposition rate of the absorption layer reach 1020 a / s.The core issue concerning the deposition rate is to prevent the increase of the photo-induced attenuation effect of the thin film while increasing the deposition rate [ 253.In addition to RF plasma enhanced chemical vapor deposition ( RFPECVD ), some other deposition techniques have also been studied to achieve sufficient film quality and higher deposition rate, such as very high frequency glow discharge VHF - GD, hot wire chemical vapor deposition HW CVD and expanded thermal plasma chemical vapor deposition ETP CVD.
Choosing the right mass production technology: Although deposition of A - Si: H absorption layer is the most important process step, the preparation steps of several other production lines also have a great impact on the total cost of solar cell modules, including deposition of TCO front contact, deposition of multilayer back contact, laser scribing of sub-SEALED BATTERY in series, lamination packaging and framing 0 solar cell structure and module design determine the choice of subsequent preparation steps and deposition process.At present, there are three main processes for depositing a - si: h absorbing layer: single chamber batch process, multi-chamber process and roll-to-roll process, each of which has its own advantages and disadvantages. " _ 18".The general trend of commercialization of amorphous silicon thin film solar SEALED BATTERY is to increase substrate size and reduce unit area cost.The experience gained by the flat panel display industry in depositing A - Si: H on large-area substrates can be transferred to the large-scale production of amorphous silicon thin film solar SEALED BATTERY.The overall requirements of its production equipment include sufficient reliability of the deposition process, higher normal operation time, higher yield and process selection for cleaning the cavity.
Reducing the cost of raw materials: the cost of raw materials accounts for a larger part of the total cost of amorphous silicon thin film solar cell modules.Glass plates or high temperature resistant polymer sheets are more expensive to use as substrate carriers, while cheaper metal sheets are suitable for continuous roll-to-roll processes.For flexible components, using a relatively thick fluoropolymer as a sealant can guarantee a 20 - year component life.Sealants account for a large part of the cost of components, so developing cheaper sealants is an important research direction of raw materials.The choice of substrate carrier determines the acceptable process temperature and process flow.If glass is used as the substrate for depositing A - Si: H, its purity and gas usage requirements will also increase the cost.For example, using Ge to prepare A - SiGe: H as an absorption layer for multi-junction SEALED BATTERY can significantly increase the cost of raw materials.
amorphous silicon
In order to better understand and design amorphous silicon thin film solar SEALED BATTERY, we need to discuss the atomic structure and material properties of amorphous silicon A - Si: H and compare them with monocrystalline silicon materials.Various techniques for determining Si: H properties will also be introduced here.5.3.1 The atomic structure of amorphous silicon A - Si: H is obviously different from that of monocrystalline silicon.In the atomic structure, the number of covalent bonds between an atom and an adjacent atom is called coordination number.The coordination number of Si atoms in monocrystalline silicon is 4;We can say that Si atoms in monocrystalline silicon are quadruple coordinated.The crystal SEALED BATTERY of monocrystalline silicon can be copied and stacked to form a regular crystal lattice, so the atomic structure is short-range ordered and long-range ordered.
Compared with monocrystalline silicon, the atomic structure of A - Si: H is short-range ordered and long-range disordered.Although most Si atoms still have four adjacent atoms connected by covalent bonds, and the atoms have similar atomic arrangement at the local atomic scale, this short-range order is the same as that of monocrystalline silicon, but at a longer distance scale, A - Si: H lacks a reasonable sequence structure. This atomic structure can be confirmed by X - ray diffraction measurements to have a small deviation between the bond angles and bond lengths of the adjacent atoms of A - Si: H, so that the local atomic structure completely loses its order within the distance range of more than a few atoms. Such an atomic structure is called a continuous irregular network.Because of short-range order, conventional semiconductor concepts such as conduction band, valence band and state density are still applicable to a - si: h.
A - Si: A covalent bond with a large deviation in bond angle and bond length between adjacent atoms in H becomes a weak bond.If there is enough energy ( e.g. thermal energy ), weak bonds will break easily, and this process will form defects in the atomic network.In crystals, any atom that leaves the lattice position is called a defect.However, the definition of defects in a _ si: h continuous irregular network is different from that of crystals, and atoms do not leave their original positions [ 268and defects appear as s!The atom is no longer a quadruple coordination, probably a triple coordination, but only has a covalent bond with the adjacent three Fen atoms, with one unpaired electron forming a dangling bond.
In pure A - Si ( amorphous silicon with Si atoms but no other atoms ), there is a defect density of about 1021 cm - 3. Materials with such a large defect density cannot be used as semiconductor devices.If H is combined with the atomic network in the process of depositing A - Si by glow discharge with SiH4, H atoms will form covalent bonds with most dangling bonds, and the intensity of Si - H covalent bonds is greater.After hydrogen passivation of dangling bonds, the defect density will decrease from 1021 cm " 3 of pure a - si to 10151016 cm _ 3 of a - si: h, which is equivalent to < 1 dangling bond per 1 million si atoms.Only such Si / H alloy materials can make doping effective and suitable for electronic applications.
electron spin resonance
Electron spin resonance ( ESR ), as an advanced experimental technique, can reflect the microstructure of defects in semiconductors and is suitable for measuring the defect density of amorphous silicon a - &: h!ESR measurement of A - Si: H can better identify neutral dangling bonds [ 26' 28 ].Because ESR results are very clear, this experimental method is considered as a standard technique for determining A - Si: H defects.However, ESR sensitivity is limited to thin films with low spin density and can only give information about paramagnetic defects ( defects with unpaired electrons ).For this reason, ESR underestimates the defect density because charged dangling bonds do not have unpaired spin signals.Therefore, ESR results are very dependent on the Fermi level position that determines the occupation of defective electrons.
Hydrogen in Amorphous Silicon
Because H is very important for defect passivation, the mechanism and stability of H in the A - Si: H atomic structure of amorphous silicon are the focus of current research.Infrared absorption spectrum has been widely used to study Si - H. R bonding mode 610 in A - Si: H. The three most obvious characteristic peak bands in the A - Si: H infrared absorption spectrum can be observed as follows:
The peak value of CM - 1: the vibration mode corresponding to Si - H, Si - H2, Si - H3 and ( Si - H2 \, covalently bonded mode, can be used to determine the H content of A - Si: H [ 18 ];Double peak value of 840890 cm _ 1: rocking mode corresponding to Si - H2 bonding mode;Several peaks of 20002200 CNC1: the peak of 2000 cm - 1 corresponds to the low tensile modulus ( LSM ) of the isolated Si - H bonding mode, while the peak of 20602160 CRRT 1 corresponds to the high tensile modulus ( HSM ) of the interface Si - H2, Si - H3 and voids.
From the absorption peaks of LSM and HSM, the microstructure parameters ( microstructuremeter, j * ) can be obtained.R' is widely used to describe the microstructure of A - S: H network, and can roughly indicate the proportion of HSM and LSM phases:
Where JHSM and / LSM are respectively high tensile modulus integral absorption strength and low tensile modulus integral absorption strength.Overall, the h atom content of the device mass a - si: h is less than 10 %, and the diffusion change measurement of r' < 0. loh atoms can describe the migration movement, trap capture and concentration change l29 of h atoms in a - si: h ..Nuclear Magnetic Resonance ( NMR ) can also give information about the local atomic environment in which H atoms exist [ 3 \ Based on NMR experiments, it has been confirmed that H in molecular composition accounts for 405.3.2 state density of H in A - A: H. A basic concept describing carrier concentration and distribution in semiconductor materials is the state density of quantum state distribution.For ideal intrinsic crystal silicon, the valence band and conduction band are strictly separated by the band gap, and no energy state is allowed in the band gap.Due to the long-range disorder of the A - Si: H atomic structure of amorphous silicon, the energy states of the valence band and conduction band extend into the band gap, forming an energy level region called " tail state".Moreover, the defect state forms a local energy state in the central region of the band gap between the valence band and the conduction band.This means that there is a continuously distributed state density in A - Si: H, and there is no strictly defined band gap between the valence band and conduction band of A - Si: H ..
The wave function extending to the whole atomic structure can describe the valence band or conduction band energy states of free carriers, and these non-local energy states are called extended states.The long-range disordered A - Si: H atomic structure limits the tail state and the defect state to the local atomic network. These energy states are called local states?Mobility is often used to describe the free transport ability of carriers in semiconductors, while the mobility of local states is very small.Compared with the expanded state, the mobility of carriers in the local state decreases significantly, so the band gap in A - Si: H can be called the mobility gap.The reason for distinguishing the band gap from the mobility gap is that there is a certain state density in the mobility gap, which conflicts with the classical concept of band gap in which no energy state is allowed.The expanded state separated from the a - si: h localized state is also called mobility edge, and the mobility gap corresponding to the valence band top three or conduction band bottom a - si: h of crystalline silicon is larger than that of monocrystalline silicon, with a typical value of 1.7 - 1.8 ev.
Theoretical Models of Tail State and Defect State
In general, the energy state distribution of amorphous silicon A - Si: H can be divided into three regions:
An extended state above the conduction band mobility edge;
Extended states below the valence band mobility edge;
The local states between mobility edges, and the continuous distribution of local states is the superposition of valence band tail states, conduction band tail states and defect states. The standard theoretical model of OA - Si: H state density distribution is two similar Gaussian distributions, and the lateral distance between the two defect states is the correlation energy ( U ), then C7 is a normal number.As mentioned earlier, dangling bonds are the main defects of A - Si: H, while dangling bonds have three charge states: positively charged D +, electrically neutral D and negatively charged IT.Defects such as dangling bonds that have three possible charges will form two energy levels and others in the band profile or band structure, also known as defect energy levels ( 7 ) and E07 - depending on the position of Fermi energy levels.The two Gaussian distributions d + 〃 and e z - correspond to the + / 0 and 0 / - charge transitions of dangling bonds, respectively.Because dangling bonds can become both donor + / 0 and acceptor 0 / -, dangling bonds are also called amphoteric defects o because disordered structures will form a certain energy state distribution in the mobility gap rather than being confined to an energy state at a specific energy level, the defect state of a - si: h needs to be described by Gaussian distribution.However, the Gaussian distribution of defect states does not contain information about the mechanism of defect states.The defect pool theory is based on the bond conversion model of weak dangling bonds and can successfully describe the defect state distribution of A - Si: H [ 32 - 35 ].According to defect pool theory, the long-range disorder of amorphous network enables the energy of defect states to take a certain range of values, and defects can have different charge states. The total defect state density obtained is the sum of three energy distributions DH, DZ and recognition, DH corresponds to positively charged defects, D corresponds to electrically neutral defects, and DE corresponds to negatively charged defects.The defect pool model can predict that when the Fermi level of the intrinsic A - Si: H moves from the center of the mobility gap to the mobility side, the total number of dangling bonds will increase, and the position of the Fermi level also determines the distribution of the defect state with respect to energy.
The energy level in the band gap ( mobility gap ) will become the trap and recombination center for trapping carriers, which will have a considerable impact on many electrical properties of A - Si: H and be reflected in the performance of amorphous silicon thin film solar SEALED BATTERY.In crystalline silicon, a single energy level in the band gap often determines the recombination process.However, the generation rate and recombination rate of A - Si: H need to account for all defect states in the band gap.The composite process of local tail states can be calculated by using Sh Ockley - Read - Hall Statistics M, which describes a single energy state, while the gender defect in the center of the band gap needs to use SAH - Shocklestatics, which describes multiple energy states [ 37 ].The author has made a detailed analysis and comparison of the simulation methods of A - Si: H production rate and recombination rate [ 18 ].
Many experimental techniques have been applied to measure the state density of A - Si: H [ 26 ], while the measurement of local tail state and defect state distribution has received special attention.Although there is no direct method for measuring the energy state distribution of A - Si: H, the energy state distribution can be indirectly determined by measuring the optical and electrical properties of A - Si: H films or by the characteristics of the space charge region at the A - Si: H interface.In order to better understand the technology of measuring state density, we need to discuss the optical and electrical properties of A - S: H first.
optical property
The optical properties of amorphous silicon A - Si: H are usually described by absorption coefficient, optical band gap and refractive index.
The function of A - Si: H absorption coefficient with respect to photon energy is compared with A _ SiGe: H, P - type A - SiC: H and crystalline silicon.In the visible light band, the absorption coefficient of a _ si: h is 100 times higher than that of crystalline silicon.This means that a 1 - thick A - Si: H layer is sufficient to absorb 90 % of the available solar energy.In fact, the thickness of the active layer of the amorphous silicon solar cell is only 0.3 mm, which is 1000 times thinner than a typical crystalline silicon solar cell.
Since the unit SEALED BATTERY of the A - Si: H structure network do not have translational symmetry, the law of conservation of momentum in crystals is not so strict in A - Si: H, so A - Si: H has the characteristics of a direct bandgap semiconductor, and the absorption coefficient A of A - SUH depends on the optical transition of photon energy E between all occupied / unoccupied electron states.Therefore, light absorption measurement is widely used to determine the state density distribution of A - Si: H, and the absorption coefficient curve is very important to determine the quality of A - Si: H and / XC - Si: H films.
The absorption spectrum of A - Si: H is divided into three regions:
Region A: Light absorption comes from the transition between the valence band extended state and the conduction band extended state.The absorption coefficient of region a is " measured by reflection - transmission spectrum at 103104 cm - 1"
B region: Light absorption comes from the transition between the valence band tail state and the conduction band tail state. This region is called the Ulbach edge.The absorption coefficient of Ulbach edge in region B is 1103 cm _ 1.Although the experiment has observed that the optical matrix element does not depend on photon energy at 38 ], the absorption coefficient A at the Ulbach edge depends on photon energy E in the form of an exponential function:
Where the curve is a constant;And e.It is Ulbach energy, which describes the exponential slope of energy dependence.Because the conduction band tail distribution is narrower than the valence band tail distribution, the Ulbach energy reflects the exponential slope of the valence band tail region.Device Quality A - Si: H Thin Film Ulbach Energy E.Typical value of < 5x10 _ 2ev.
C region: the light absorption comes from the transition related to the defect state.The absorption in region C is due to the absorption coefficient reflecting the transition of internal energy states in the band gap, and regions B and C are also called sub-band gap absorption.
By the absorption coefficient of A - Si: H, the so-called " optical band gap" can be obtained.The optical band gap is a very useful material parameter for studying the optical properties of A - Si: H.In general, the higher the optical band gap of the material, the smaller the light absorption.
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