Front Terminal Telecom battery is specialized in 19 feet and 23 feet battery rack/cabinet, internet equipment, power system and LAN.
UPS backup power.
Voltage: 12V, capacity 55ah to 180ah.
Design Life: 12 years (20℃ )
Excellent high rate discharge performance
Excellent heat dispersion
Good ventilation design
Extremely low self-discharge rate, less than 1% monthly
Widely used in temperature -15℃ to 45℃
Patent terminal design, ensure the safety seal
Optional anti fire design
Telecom power system is the most important part of the whole telecom system, is like heart to human. The stability and reliability of power equipment will affect the whole telecom system and quality.
Telecom power system equipment and facility mainly includes: AC input, high and low voltage distribution, diesel generators, rectifier, battery pack, DC transformer, UPS, and various type of DC distribution board. Reasonable design and configuration is very important.
Expanded thermal plasma chemical vapor deposition
Expansion thermal plasma chemical vapor deposition ( ETP CVD ) is a remote plasma enhanced chemical vapor deposition rpecvtfm \ different from direct plasma enhanced chemical vapor deposition d PECVD where the sample is directly exposed to plasma, where the r PECVD sample is placed at the afterglow position of the plasma and the configuration of the reaction chamber is also different.ETP CVD spatially separates plasma generation from film deposition, and the reaction chamber configuration includes a high pressure plasma source and a low pressure low deposition reaction chamber.The mixed gas Ar / H2 / N2 is used as carrier gas without deposition to generate plasma through DC discharge of cascade arc.The typical power used to maintain the plasma is in the 28kW range, the pressure of the plasma source is 200700 mbar, and the typical pressure of the settling chamber is maintained at 0.10.3 mbar by roots blower and disaster wheel pump.Roots blower is a positive displacement vane pump with a pair of engaging vanes to pump liquid, which is captured around the engaging vanes and brought from the vacuum chamber to the exhaust port.The plasma is expanded from the cascade arc plasma source to the deposition reaction chamber at supersonic speed through the nozzle, and pure SiH4 is injected into the plasma jet by the injection ring several cm away from the expansion nozzle and then decomposed by the reactant emitted from the plasma source.
The flow rate of H plays an important role in the growth of high quality A - Si: H, which determines the amount of SiH3 radicals produced.The deposition rate of a _ si: h layer depends on factors such as gas flow rate and arc current, and can reach a maximum of 800a / sm in order to prepare device quality a - si: h at a high deposition rate ( > 70a / s ), it is necessary to raise the substrate temperature to about 400 c | m ..The demand for high temperature is due to the competition between deposition rate and surface diffusion during growth [ 95J.Since the ion bombardment on the growth surface is relatively mild, RF bias can be applied to the substrate, which can provide additional energy to the surface of ETP CVD deposited A - Si: H ..Ion bombardment of the surface delivered enough energy to allow the deposition temperature to decrease by about 100' c while maintaining good material properties [ 94 ].The study of ETP CVD method makes people better understand the growth of A - Si: H, surface treatment and the role of reaction gas in the growth process [ 96 ]?
In order to apply ETP CVD deposition technology to the fabrication of amorphous silicon thin film solar Telecom Battery, a cascade system with three reaction chambers was built.The three cavities in the deposition system configuration are:
RF plasma enhanced chemical vapor deposition RFPECVD deposition doping layer;Etp CVD growth of intrinsic layer.
The deposition rate of compact a - si: h thin films grown by ETP CVD with RF bias is > 10 persons / s and the substrate temperature is < 300 c.Recently, the single junction amorphous silicon thin film solar cell has achieved an initial conversion efficiency of 8.0 %, the deposition temperature of ETP CVD is 250 C, and the deposition rate is 11a / s [ 98 ].
hot wire chemical vapor deposition
Hot filament chemical vapor deposition HW CVD is also called catalyst chemical vapor deposition, which decomposes gas molecules on the hot filament by catalytic cracking reaction.The laboratory HW CVD deposition chamber with the simplest structure is similar to plasma enhanced chemical vapor deposition PECVD except that the filament is replaced by the RF electrode.The material of the filament is usually w or ta, placed near the substrate support, and the filament temperature of > 1600 c can effectively decompose sih4 into si / h radicals.The deposition composition of traditional PECVD is caused by the collision of high energy electrons and gas molecules, while the deposition composition of HW CVD is different from PECVD, and the properties of amorphous silicon A - Si: H film obtained are also different from PECVD.NREL, the National Renewable Energy Laboratory of the United States, confirmed that HW CVD with substrate temperature higher than RFPECVD can produce A - Si: H films with H atom content much lower than the optimal value of 10 %, while the electrical quality such as Ulbach energy and defect density of A - Si: H films are similar to those of PECVD device quality materials ⑽ \ Because the H atom content of HW CVD is very low, even only 1 %. The deposited films are relatively stable in terms of photo-induced attenuation effect, which has aroused widespread interest in the research of HW CVD deposition technology today, and many scientific research teams around the world have used HW CVD to prepare A - Si: H and MC - H films.
In contrast to ETP CVD - like, HW CVD - also requires the preparation of device quality A - Si: H thin film EL 2 at a higher temperature than PECVD.The a - si: h thin film prepared at 380 c substrate temperature and a / s deposition rate has a low defect density of 1016 CNT3 and a low h atom content of < 5 %.Recently, a - si: h thin film was also successfully prepared at a relatively low substrate temperature of 250 c, and the hydrogen - silane dilution ratio of the raw crystalline silicon prepared by conventional PECVD was only high and the deposition rate was low, about 3a / s, but pure sih4 can be used for depositing the raw crystalline silicon by hw CVD at Utrecht university in the Netherlands, and a high deposition rate ( about 10a / s ) o combined with such hw CVD raw crystalline silicon n - I - p amorphous silicon thin film solar cell was achieved at 250 c substrate temperature in 1500 h.The stability of this photo-induced attenuation effect should be attributed to the special hole characteristics and the enhanced medium-range order [ ] 3 \ HW CVD prepared N - I - P type single junction amorphous silicon thin film solar cell achieves the laboratory record of 9.8 % of the initial conversion efficiency, and the deposition rate is 16.5a / s [ off.Recently, P - I - N type single junction amorphous silicon thin film solar Telecom Battery prepared by HW CVD on glass / S NO2: F substrates also showed excellent performance, with the deposition rate of 32 persons / s reaching 7.5 % of the initial conversion efficiency and the deposition rate of 16 persons / s reaching 8.5 % of the initial conversion efficiency [ 1.5 ].
The excellent characteristics of several aspects of HW CVD process are very suitable for commercial mass production:
Higher deposition rate;
high gas utilization rate;
The lower air pressure process can avoid the formation of dust or powder, thus improving the cleaning cycle of the cavity.Multi - filament or filament net realizes a large deposition area [ 1?;Separate gas decomposition from substrate deposition [ 1 7 ].
The main problems to be solved in upgrading HW CVD technology to mass production are:
Uniformity of large area deposition;
Filament is easy to age and has short service life.
Filament contamination of growing films.
Recent developments show that these problems have been successfully solved, and Japan's pine industry has begun to use HW CVD system for large-area deposition [ 1 6 ].
amorphous silicon thin film solar cell
Structural Design of Amorphous Silicon Thin Film Solar Cells
The carrier diffusion length of amorphous silicon A - Si: H is much shorter than that of crystalline silicon, and the bipolar diffusion length of device quality intrinsic A - Si: H is in the range of 0.1 - 0.3.In the doped A - S: H layer, the defect density caused by doping is 23 orders of magnitude higher than that of intrinsic A - Si: H, and the minority carrier diffusion length is very low.Like crystalline silicon solar Telecom Battery, solar cell structures that rely on minority carrier transport in the p - n junction electrically neutral region are not suitable for amorphous silicon thin film solar Telecom Battery.Due to the short diffusion length, the photo-generated carriers in the doped A - Si: H layer will all recombine before reaching the P - N junction depletion region.Therefore, the structural design of amorphous silicon thin film solar Telecom Battery is completely different from the standard p _ n junction of crystalline silicon solar Telecom Battery.
Diagram of the structure of a single junction amorphous silicon thin film solar cell.The device is a P - I - N junction comprising three parts:
P - type A - SiC: H layer;
Type I A - Si: H layer;*
N type A - Si: H layer.First, the doping layer is usually very thin, the p - type a - sic: h layer is about 10 nm thick, and the n - type a - si: h layer is about 20 nm thick. the doping layer of amorphous silicon thin film solar Telecom Battery has two functions:
The dope layer form built-in electricity in that range of the intrinsic a - si: h layer
( 3 ) The photo-generated carriers in the V - Si: H layer are collected, and the built-in electric field strength depends on the doping concentration of the doping layer and the thickness of the intrinsic layer.The doped layer establishes a low-loss ohmic contact between the A - Si: H portion of the solar cell and the external electrode, so both the N - type layer and the P - type layer need sufficiently high conductivity so that the built-in voltage in the P - I - N junction range is sufficiently high and the resistance in contact with the electrode is sufficiently low.
The intrinsic layer with an optical band gap of about 1.75 eV has the function of an " absorption layer".The electron-hole pairs generated in the absorption layer are separated into free electrons and holes by the built-in electric field.The material quality of the intrinsic layer and the intensity distribution of the built-in electric field determine the collection of photo-generated carriers and the characteristics of amorphous silicon thin film solar Telecom Battery.The electric field distribution of the absorption layer is very dependent on the defect density distribution in the intrinsic layer and at the interface with the doped layer.The electrons move toward the N - type layer while the holes move toward the P - type layer, and the photo-generated carriers are collected by the electrodes after entering the doped layer.Because the main transport mechanism of photogenerated carriers is drift in the built-in electric field, amorphous silicon thin-film solar cell is also called drift device 0, which determines the optimal thickness of intrinsic A - Si: H layer and is a key part of the structural design of amorphous silicon thin-film solar cell.The thickness of the intrinsic layer depends on the careful trade-off between photon absorption and carrier collection, because a thicker intrinsic layer facilitates photon absorption.while a thinner intrinsic layer is advantageous for the collection of photo-generated carriers.Since the collection of carriers depends on the drift of light-generated carriers in the built-in electric field, the mobility and lifetime of carriers and the strength of the built-in electric field within the intrinsic layer determine the collection of carriers.The Fermi level position of the doped layer largely determines the built-in voltage within the device range, and the built-in voltage and the intrinsic layer thickness together determine the built-in electric field strength.However, the built-in electric field is not uniform within the intrinsic layer.It strongly depends on the distribution of space charges in the intrinsic layer, while the space charges in the intrinsic a - si: h layer are caused by carriers trapped in the tail state and defect state in the band gap, and these space charges cannot be ignored as in crystalline silicon solar Telecom Battery.Due to the high state density of local states in the band gap, the charge trapped by these local states contributes greatly to the overall charge distribution of the device and determines the built-in electric field distribution.The higher defect density at the interface with the doped layer will result in a higher electric field strength in these interface areas, while the electric field strength in the intrinsic layer is relatively low.Effect of two different defect density distributions in 320 nm thick intrinsic layer on internal parameters and volt-ampere characteristics.ASA software developed by Delft University of Technology in the Netherlands simulated internal parameters ( band structure, electric field intensity distribution and voltage distribution ) according to two different defect density distributions, as well as volt-ampere characteristics of two solar Telecom Battery in the dark and under light [ 1 8 ].In the standard model, the defect density distribution within the intrinsic layer is uniform, while in the defect pool model ( DPM ), the defect density distribution and defect state energy distribution are calculated according to the defect pool theory ( see section 5.3.3 ).The difference between the standard model and DPM model is only that the description of the defect state is different, and other input parameters are the same.
Under the illumination, the higher concentration of photogenerated carriers will also affect the space charge in amorphous silicon thin film solar Telecom Battery.When the concentration of photogenerated carriers is too high, holes with low mobility will form a large amount of space charges, which will cause the electric field on the back surface of the Telecom Battery to collapse.According to the computer simulation [ 1 9 ], when the thickness of the intrinsic layer increases, the power of the solar cell will be saturated, and the saturation of the power depends on the absorbed human light intensity.For highly absorbed human photons with photon energy of about 2.3 ev, the thickness of power saturation is > 100 nm, which is a typical distance for photons to be absorbed.For low absorption human photons with photon energy of about 1.8 ev, the thickness of power saturation is > 300 nm, which is the collection length of carriers, which depends on the product of electric field strength, carrier mobility and lifetime.The asymmetry of electron and hole drift given by computer simulation also explains why the amorphous silicon thin film solar cell receiving human light from the P - type layer has higher conversion efficiency.S - W effect will increase more defects in the intrinsic layer, reduce carrier lifetime and change electric field distribution, thus affecting carrier collection.The optimum intrinsic layer thickness of a single junction amorphous silicon thin film solar cell is 250320 nmc 92' 110 ]
Upper layer configuration and substrate configuration
The basic configuration of amorphous silicon thin-film solar Telecom Battery is divided into P - I - N upper-layer configuration and N - I - P substrate configuration. Their technological differences are mainly reflected in the deposition sequence of amorphous silicon A - Si: H thin films.In the P _ I _ N upper layer configuration, a P - type layer is deposited first, then an intrinsic layer, and finally an N - type layer is deposited.In the N - I - P substrate configuration, the order of deposition is reversed.In the upper layer configuration, the deposition sequence of P - I - N requires a transparent substrate carrier, and the common substrate carrier is a glass plate plated with a transparent conductive oxide TCC film.The TCO film as a front contact needs to meet several strict conditions:
High transmittance ( A _ Si: H absorbing amplitude is in 350 - 800N m band, while A - SiGe: H absorbing IFJJG is in 350 - 1000 nm band );Low square resistance;
In addition, the TCO layer needs surface texturing so that scattering of the internal rough interface can increase light absorption in the solar cell.The use of glass substrates allows the deposition temperature of TCO films to reach up to 600 C, at which high quality S NO2: F films can be prepared as TCO layers using atmospheric chemical vapor deposition APCVD.The P - I - N type A - Si: H layer is deposited on the TCO layer on the front surface, while the back contact metal layer cannot be deposited directly on the N type layer but needs to be deposited on the TCO intermediate layer.The TCO intermediate layer can improve the reflectivity of the back contact by matching the refractive indices of the N - type A - Si: H layer and the metal layer, and can prevent Si and metal from intermixing with each other.The laminated packaging of solar Telecom Battery arranged on the upper layer is often completed by covering the back surface with a sealant or another glass plate.
In the substrate configuration, the substrate carrier forms the back surface of the amorphous silicon thin film solar cell so that an opaque stainless steel sheet or polymer sheet substrate, such as a high temperature resistant polyimide, can be used.The substrate carrier may be a sufficiently thin flexible material, which makes it possible to apply the roll-to-roll process.It is necessary to deposit a back contact of the textured surface on the substrate carrier, and the back contact consists of an Ag or A1 metal layer and a TCO layer.The purpose of preparing the textured surface of the back surface is to scatter the reflected light back to the absorption layer through total reflection so that the cell can fully absorb photons.In the case of stainless steel sheet as substrate carrier, the best surface texture can be obtained by depositing Ag and ZnO bilayer films in 200350 C temperature range [ 14 ].After depositing the A - Si: H layer according to the N - I - P sequence, a TCO front contact with metal gate lines is formed on the surface of the P - type layer.The front surface of the substrate configuration Telecom Battery is transparent sealant, and another glass plate can be optionally covered on the sealant.The use of conductive substrate carriers such as stainless steel sheets can make the monolithic interconnection on the substrate more complicated.
As a matter of fact, batteries with glass plates as carriers are often designed for the upper layer configuration, while batteries with flexible metal sheets or polymer sheets as carriers are often designed for the substrate configuration.Therefore, the production technology of amorphous silicon thin-film solar Telecom Battery is obviously divided into two technical routes: glass plate upper layer configuration technology and flexible carrier substrate configuration technology.
High conversion efficiency technology
Since only the light absorption of the amorphous silicon A - Si: H intrinsic layer contributes to the generation of current, the optimal light absorption design of the solar cell structure needs to maximize the light absorption of the intrinsic layer and minimize the light absorption of other layers, and such a design needs an adequate light trapping structure.In addition to the trapping structure, other methods are needed to improve the collection of photogenerated carriers.The following are some important high conversion efficiency technologies for preparing amorphous silicon thin film solar Telecom Battery, and the relevant cell structure is shown in actual .11.
Since the mobility of holes in A - Si: H is lower than that of electrons, most photogenerated carriers are generated at the front end of the solar cell.The distance between holes and the collecting electrode needs to be shorter than that of electrons, so human light should enter the amorphous silicon thin film solar cell through the P - type layer. Such a P - I - N junction design can improve the collection efficiency of holes.
Since human light enters the solar cell through the P - type layer, the P - type layer has the advantage of absorbing photons.However, the photogenerated carriers in the P - type layer do not contribute to the photogenerated current because minority carrier electrons will recombine quickly.The method of reducing the light absorption of the P - type layer is to reduce the thickness and form an alloy with C. The optical band gap of the P - type A - SC: H layer is about 2eV, which acts as a window layer.
The performance of solar Telecom Battery is very sensitive to the P - I interface region.In the heterojunction of the P - I interface region, a band step is formed between the band of the wider band gap P - type layer and the narrower band gap intrinsic layer, and the band step of the valence band will become a barrier for photogenerated holes to enter the P - type doped layer.The carrier generation rate in the P - I interface region is the highest in the intrinsic layer.A lot of research has been done on the compatibility band order of the P - I interface region to optimize the electric field intensity distribution in this region and prevent photogenerated electrons from diffusing backward toward the P - type layer.Usually, an intrinsic or lightly doped A - S: H or A - SiC: H layer with wide band gap, thin thickness and high quality is introduced at the P _ I interface as a buffer layer, which acts as a diffusion barrier layer to prevent B atoms from diffusing from the P - type layer to the intrinsic layer.
The substrate on which the A - Si: H layer is deposited needs surface texturing. The surface texturing of the front contact TCO layer in the upper layer configuration and the back contact TC ( ) / metal layer in the substrate configuration introduces a certain rough interface for depositing the absorption layer.When human light reaches the rough interface, most of it will scatter along all directions, thus increasing the average optical path length in the absorption layer and improving light absorption.
The back contact composed of ZnO layer and Ag metal layer has high reflectivity and can increase the light absorption to > 600 nm wavelength band.
Transparent conductive oxide
At present, the key research area of amorphous silicon thin film solar Telecom Battery is to further develop and apply effective light trapping structures.In order to effectively capture human light in the absorbing layer, the light trapping structure uses a rough interface, a high reflectivity back contact and a refractive index matching layer to reflect light in the cell many times.Light scattered through the rough interface and reflected by the front and back surfaces for many times has a longer average optical path length in the absorbing layer. These trapping effects can effectively increase the light absorption of P - I - N to human light and increase the photogenerated current of the solar cell.Readers who are interested in this can refer to schropp and ze man's detailed discussion on the optical design of amorphous silicon thin-film solar Telecom Battery. the transparent conductive oxide TCO layer is an important light trapping structure and currently determines the conversion efficiency of the most advanced amorphous silicon thin-film solar Telecom Battery.Developing TCO materials that meet certain optical, electrical and optimal surface texture is now the most important research field of silicon-based thin film solar Telecom Battery.
In the upper layer configuration, the TCO layer introduces the rough interface into the solar cell, and as the TCO layer for the front contact, several material characteristics must be met, as shown in actual .2.In the past, atmospheric chemical vapor deposition ( APCVD ) technology has been used to deposit S NO2: F with textured surface at 500 C as the front contact TCO layer.At present, Japan Asahi's so-called U - shaped S NO2 thin film has become a reference substrate in the field of silicon-based thin film solar Telecom Battery [ 112 ], but this optimized TCO substrate material has not yet been mass produced.Recently, ZnO has attracted wide interest. Due to its low deposition temperature ( < 300' c ), it has stable performance for H plasma and high temperature process and has the potential to become a substrate material to replace S NO2.Moreover, the ZnO layer also has a barrier layer function to prevent impurities from diffusing from the substrate to the absorption layer.The cost of ZnO is lower than most TCO when its optical and electrical properties are similar to those of other TCC materials.The deposition techniques of ZnO thin films include LPC VTF 19 by low pressure chemical vapor deposition, ETP CVD 13 by expanding thermal plasma chemical vapor deposition and sputtering [ 2D ].The surface texture of ZnO naturally forms [ LM13 ] during the growth process, and can also be prepared by chemical etching after deposition [ 2 ].The stability of ZnO in H plasma allows amorphous silicon A - Si: H and microcrystalline silicon MC - Si: H films to be deposited in H - rich plasma.Sputtered ZnO: Al has an optical band gap of about 3.45, and its value depends on electrical properties such as mobility, carrier concentration and Burstein - Moss shift.Burstein - Moss shift is the optical band gap shift of semiconductor material caused by doping.
The interface region of TCO - P layer has a great influence on the characteristics of amorphous silicon thin film solar Telecom Battery on the upper layer [ M ].Depositing P - type A - SiC: H layer will reduce the S NO2 layer, thus limiting the short-circuit current density of the cell. The reduction effect is especially obvious at high deposition temperature and high H dilution.Therefore, a very thin ZnO layer is often deposited on the surface of S NO2 thin film to prevent reduction in H - rich plasma.The ZnO layer plated on the S NO2 surface will increase the number of people, but it will also reduce the open-circuit voltage VOC and the filling factor FF of the Telecom Battery, because the P - type layer and the heterojunction of degraded N - type ZnO are obviously depleted, thus forming a contact barrier with ZnO and lowering the built-in voltage of the Telecom Battery.The problem of ZnO - P type layer contact can be solved by using Si interlayer with high conductivity.
In an amorphous silicon thin film solar cell with a substrate configuration, a roughened interface is introduced in the solar cell by a textured back mirror.However, increasing the surface texturing of the back mirror will not increase the current [ 115 ], and increasing the texturing - enhanced back contact light absorption will limit the current, which can be explained by surface plasma absorption [ 116 ].If a stainless steel sheet is used as the substrate, a better surface texture can be obtained by depositing Ag and ZnO bilayer films at 200350 C temperature.
The front surface TCO film needs to be designed with minimum light absorption and minimum light reflection, so the thickness of the TCO film needs to meet the minimum reflectivity:
In the formula, the typical TCO film has a refractive index of about 2, which means that the TCO film thickness reaching the minimum reflectivity is about 80 nm.However, such TCO thickness cannot provide sufficiently low resistance, so it is necessary to apply an applied current collection scheme, such as preparing a metal gate line on top of the TCO layer, or a special current collection design such as SERIESCONNONTIONHROUGHHAPERPERPERFORMEDOFILM ( SCAF ) [ L3 ].
The surface texture of TCO film depends on deposition conditions and post-deposition treatment, and varies greatly.Scanning electron microscope ( SEM ) is a common electron microscope.The sample surface is scanned in a raster pattern by a high-energy electron beam and an image is formed.Electrons interact with the atoms that make up the sample, and the resulting signals contain information such as the surface morphology, composition and conductivity of the sample.Since it is confirmed that the use of textured substrate surface can increase the photogenerated current of amorphous silicon thin film solar Telecom Battery [ 1 ], a large amount of research work has focused on the effect of TCO thin film surface morphology on the photogenerated current of the Telecom Battery.People focused on the light scattering process of the rough TCO film and found the relationship between the rough interface morphology and scattering parameters " 117 - 119".Most of the knowledge about scattering characteristics of rough interface comes from computer modeling o because multiple scattering processes occur at the internal rough interface, optical modeling has become a powerful tool for analyzing and optimizing complex optical phenomena of amorphous silicon thin film solar Telecom Battery [ 118' 12 ].The simulation results have clearly demonstrated the effect of the suede surface of the front and back contact surfaces and the selection of the back contact material on improving the current of the solar cell.At the same time, the computer modeling also analyzes the light loss of the non-photovoltaic layer of the solar cell.In general, the increase in spectral response in the 450 - 600 nm wavelength range comes from scattered light from the front contact interface, while scattering from the back contact plays a major role in the > 600 nm wavelength range.Therefore, both the front and back contact interfaces must be sufficiently rough.
thereby improving light absorption over the entire wavelength spectral range.Even if no antireflection film is deposited, the antireflection film characteristic of the rough interface makes the reflectivity of the whole cell smaller, which is due to the refractive index distribution of the rough interface [ 12 ].
S - W effect
S - W effect ( photo - induced attenuation effect ) will reduce the performance of single-junction amorphous silicon thin-film solar Telecom Battery in the initial stage of operation, but after initial attenuation, the performance of solar Telecom Battery tends to be stable, and the stable output power of high-quality amorphous silicon thin-film solar Telecom Battery is 70 % 85 % of the initial value.On the other hand, the attenuation of S - W effect can be recovered by annealing.Therefore, special attention needs to be paid to the reported conversion efficiency of amorphous silicon thin film solar Telecom Battery, whether it is the initial conversion efficiency immediately after deposition or the stable conversion efficiency after photo - aging.The conditions of photoaging treatment are somewhat different in different countries.Japan's " Temporary Determination of Stable Conversion Efficiency" defines the light aging treatment conditions as: 310 h exposure to 1.25 solar human light intensity, 48 C temperature, open circuit condition.The stable conversion efficiency in the United States defines the light aging treatment condition as 600 h continuous exposure to 1 sun, 50 c temperature and open circuit.In the field of solar energy, one sun means the incident light intensity of 1000 W / m2 sunlight.
The attenuation of amorphous silicon thin film solar Telecom Battery caused by illumination is caused by S - W effect, and the metastable defects added in the absorption layer become the trap state composite center.The increased trap state changes the space charge distribution of the intrinsic A - Si: H layer, thus distorting the built-in electric field in the intrinsic layer and reducing the drift and collection ability of P - I - N pair carriers.Therefore, the structure of amorphous silicon solar Telecom Battery and the characteristics of P - I - N junctions need to be optimized after photo - aging.
The thinner absorption layer can reduce the performance attenuation of S - W effect, which will increase the built-in electric field of intrinsic A - Si: H layer and reduce the influence of space charge distribution distortion.However, the application of thinner absorption layer will reduce the light absorption, thus reducing the short-circuit current density of the Telecom Battery.One way to overcome the tradeoff between carrier generation and carrier collection is to effectively trap light, while the other way is to stack up multi-junction cell structures.Through the accumulation of top and bottom Telecom Battery and even middle Telecom Battery, the total thickness of multi-junction Telecom Battery is the same as that of single-junction Telecom Battery, but the overall light absorption is greatly improved.Because the top, middle, and bottom Telecom Battery in the stack are thinner, multi-junction Telecom Battery are less sensitive to the increased density of photoinduced attenuation defects.
At present, the A - Si: H absorption layer with the highest stable conversion efficiency obtained by a single junction amorphous silicon thin film solar cell has a thickness of 250320 nm, and the optimal thickness mainly depends on the effect of the light trapping structure.The University of New Chastel in Switzerland has achieved the highest stable conversion efficiency record of 9.47 % for a single-junction amorphous silicon thin-film solar cell with a substrate configuration [ 92 ], and its volt-ampere characteristic curve and quantum efficiency under illumination are shown in the actual figure of 14.
Multi - junction amorphous thin film solar cell
The purpose of introducing the concept of stacked Telecom Battery is to increase the output voltage of amorphous silicon thin film solar Telecom Battery [ 6 ].Later, people realized that stacked Telecom Battery can also improve the stability of amorphous silicon thin film solar Telecom Battery [ 121 ].Laminated Telecom Battery, also known as double-junction Telecom Battery ( DualJunction or DoubleJunction ), refer to stacked Telecom Battery with two P - I - N junctions.The triple junction Telecom Battery has three P - I - N junctions.The structure of multi-junction Telecom Battery is much more complicated than that of single-junction Telecom Battery.There are two key requirements for the good operation of multi-junction amorphous silicon thin film solar Telecom Battery:
The current generated at the maximum power point needs to be equal in each element Telecom Battery to realize current matching.The internal series connection between the component Telecom Battery must have low electrical and optical losses.
In multi-junction amorphous silicon thin film solar Telecom Battery, N - P junction is often used to realize the internal series connection of different element Telecom Battery, and carriers recombine with opposite charge carriers from adjacent element Telecom Battery?so as to transfer carrier to that Telecom Battery of the next element.The tunneling effect of the doped layer contributes to carrier recombination, so such a semiconductor junction is called a tunnel recombination junction.
Since the element Telecom Battery are connected in series with each other as current sources, multi-junction amorphous silicon thin film solar Telecom Battery require current matching.The component Telecom Battery with the lowest current often determines the net current of the multi-junction Telecom Battery.In order to avoid current loss, each element cell must generate equal current, and the current generated by the element cell mainly depends on the thickness of the absorption layer, so current matching can be realized by adjusting the thickness of the absorption layer of each element cell.In order to analyze the more complex current matching of multi-junction batteries.And determining the optimal absorption layer thickness requires computer modeling [ 1 8 ].
The interface between each element cell of the multi-junction amorphous silicon thin film solar cell is treated by tunnel junction.When the Telecom Battery is biased in the forward direction, the interface is N - P junction connected in the opposite direction, and ohmic contact rather than rectifying contact is made between the element batteries, so that the stacked Telecom Battery can operate normally.By preparing the tunnel junction, ohmic contact can be formed between the element Telecom Battery.The tunnel junction can ensure complete recombination of electrons reaching the N - type layer of the top cell and holes reaching the P - type layer of the bottom cell, and recombination of photo-generated carriers at the interface can enable current to flow through the entire solar cell.The high electric field strength of the reverse bias N - P junction is favorable for carriers to enter the defect states of the tunnel composite junction under the tunneling effect, and effective carrier recombination occurs in these defect states.The tunnel junction is prepared by depositing a microcrystalline silicon MC - Si: H film on the surface of at least one doped layer to obtain a better ohmic contact [ 121' 122 ].Another method is to combine a thin oxide layer between the two element Telecom Battery to function as an effective tunnel composite layer [ 123 ].If the N - P junction is a high quality ohmic contact, the open circuit voltage of the stacked Telecom Battery is the sum of the open circuit voltages of each element cell.In this way, the optimization of stacked Telecom Battery will be simplified to the optimization W of component Telecom Battery.
Multi - junction amorphous silicon thin-film solar Telecom Battery have a unique advantage in that the absorption spectrum range of each element cell can be customized to correspond to different parts of the solar spectrum, so that absorption layers with wider or narrower band gaps than the intrinsic A - Si: H can be matched with each other to achieve more effective utilization of the solar spectrum.The element cell with wider absorption layer band gap can convert higher energy photons into higher open-circuit voltage, while the element cell with narrower absorption layer band gap can absorb red light or near-infrared light and obtain lower v.The spectral decomposition method can achieve higher conversion efficiency than the single junction Telecom Battery.
Laminated Telecom Battery
Multi - junction amorphous silicon thin film solar Telecom Battery have used a combination of several absorption layer materials.The first laminated Telecom Battery uses the same amorphous silicon A - S: H material as the absorption layer of the element Telecom Battery, and the 3 - Fen: Ri / 3 - Yi: Bu 1 laminated Telecom Battery is called the same band gap laminated Telecom Battery.Compared with laminated batteries using different band gap absorbing layers, A - Si: laminated batteries have the advantages of simple preparation method and low cost, while the disadvantage is relatively low conversion efficiency.A - Si: H / A - Si: H laminated Telecom Battery has a stable conversion efficiency of 10.1 % for the upper layer configuration and the substrate configuration, respectively.
Laminated Telecom Battery with theoretical conversion efficiency limits require the absorption layer material combination of the top cell and the bottom cell to have band gaps of 1.7 eV and 1.1 eV, respectively [ 125' 23 ].The wide band gap intrinsic hydrogenated amorphous silicon carbon A - SiC: H layer is not an ideal top cell absorbing layer material because its defect density increases with the increase of optical band gap.The A - Si: H material also has a wide optical band gap ( 1.80 eV ), the deposition temperature is relatively low, and the A - Si: H material with a high hydrogen - silane dilution ratio has been proved to be the most ideal absorption layer material for the top cell [ 85' 773 ].
At present, hydrogenated amorphous silicon germanium A - SiGe: H and microcrystalline silicon MC - Si: H are used as low band gap absorption layers.- Si: H is widely used in laminated batteries and can form non-microcrystalline laminated batteries ( see Section 4.3.3 ).The disadvantage of A - SiGe: H is that its electrical characteristics deteriorate with the increase of Ge content, and A - SiGe: H with band gap less than 1.4 eV cannot have enough electrical characteristics.Through the alloy, the defect density of A - & Ge: H will increase, and the filling factor of component Telecom Battery will decrease.These problems should be considered in the current matching process. Stacked Telecom Battery need to match the maximum power point after photoaging, so the short-circuit current density of component Telecom Battery is only a rough reference for current matching.
Moreover, the interface between the doped layer and the A - SiGe: H layer will attract a larger band level.For example, there is a band order of 0.5 eV between a typical P - type A - SiC: H layer with an optical band gap of 1.95 eV and an A - SiGe: H layer with an optical band gap of 1.45 eV.These band gaps are believed to hinder effective photo-generated carrier collection.In order to overcome these transport barriers, it is necessary to form a complex Ge concentration distribution and a graded layer # 126,127 in the interface region.
The current matching conditions of A - Si: H / A - SiGe: H laminated Telecom Battery are: the top Telecom Battery A - Si: H absorbing layer thickness is 100150 RNN, while the bottom Telecom Battery A - SiGe: H absorbing layer thickness is 120150 nm.The advantage of using a combination of a _ si: h and a - sige: h is that the total thickness of the absorption layer is less than 300 nm.For the best results of laboratory conversion efficiency of the upper layer configuration and substrate configuration of A - Si: H / A - SiGe: H laminated Telecom Battery, see actual .3.
The further optimization of A - Si: H / A - SiGe: H laminated Telecom Battery comes from:
More effective light trapping effect;
adjusting the optical band gap of the absorption layer;
Composition control of A - SiGe: H materials;
The light loss of the transparent conductive oxide TCO layer and the doped layer is reduced.
If these methods are applied, the short-circuit current density of the laminated Telecom Battery can be further increased and the total thickness of the absorption layer can be reduced [ 12 ].
Triple junction Telecom Battery
If a third layer of element Telecom Battery is added to the stack, the resulting triple junction cell has a higher conversion efficiency.So far.The highest stable conversion efficiency of amorphous silicon thin-film solar Telecom Battery is realized by the U.S. Uni - Solar substrate configuration with triple junction Telecom Battery stacked as A - Si: H / A - SiGe: H / A - SiGe: H, and stainless steel sheets as flexible substrates.If we compare the quantum efficiency of the triple junction Telecom Battery with that of the single junction Telecom Battery, we can clearly see that the triple junction Telecom Battery effectively uses a wider spectral region.Uni - Solar also reported a triple junction Telecom Battery with an initial conversion efficiency of 15.2 %, indicating that it is possible to further improve the stable conversion efficiency W ..Wireless load sharing of single phase telecom inverters
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