JPH06151908A - Method of sealing defect of solar battery - Google Patents

Abstract

PURPOSE:To improve the solar battery property such as the conversion efficiency of an photo-electric transfer element by sweeping voltage so that the increase speed of a current may be at a specified value or less thereby depositing resin. CONSTITUTION:Deposited resin 110 is used for insulating the defective sections 109 by short circuit, shunt, etc., being caused by the pin hole of a semiconductor layer, the grain boundary of a polycrystalline semiconductor, the spike-shaped defect of a substrate, a lower electrode 102, etc., and other causes, and further it has a function of improving moisture resistance at the same time. The deposited resin needs to be stacked directly on the defective section, so it is stacked on a semiconductor layer 105, but as the process of deposition, the deposition may be performed after formation of an upper electrode 106. Though the deposition is performed, using constant voltage method or constant current method, the increase speed of a current in the deposition process is 10mA/cm<2>/ sec or less. Hereby, the solar battery property such as the conversion efficiency, etc., of a photo-electric transfer element can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable defect sealing method for solar cells. More specifically, the present invention relates to a method for repairing a short circuit or a shunt that occurs in a solar cell manufacturing process and manufacturing a solar cell having high initial characteristics and high reliability.

[0002]

2. Description of the Related Art Solar cells, which are photoelectric conversion elements that convert sunlight into electric energy, are widely applied as a power source for consumer appliances such as calculators and wristwatches, and also substitute fossil fuels such as petroleum and coal. It is drawing attention as a technology that can be put to practical use as power for use.

A solar cell is a technique utilizing the diffusion potential generated at a pn junction of a semiconductor. A semiconductor such as silicon absorbs sunlight to generate photo carriers of electrons and holes, and the photo carriers are pn. It is taken out to the outside by drifting by the internal electric field generated by the diffusion potential of the junction.

In manufacturing a solar cell, almost the same process as in manufacturing a semiconductor element is used. Specifically, a p-type or n-type valence electron controlled silicon single crystal is produced by a crystal growth method such as the CZ method, and the single crystal is sliced to produce a silicon wafer having a thickness of about 300 μm. Further, a pn junction is formed by forming layers of different conductivity types by an appropriate means such as diffusing a valence electron control agent so as to have a conductivity type opposite to that of the wafer.

However, since the solar cell manufacturing method uses the same process as the semiconductor element manufacturing, the production cost is high and the cost is higher than that of the existing power generation method. Under such circumstances, cost reduction is an important technical issue in the practical application of solar cells for electric power, and various studies have been made. In terms of materials, materials such as lower cost materials and materials with higher conversion efficiency are being sought, and tetrahedral amorphous semiconductors such as amorphous silicon, amorphous silicon germanium, and amorphous silicon carbide, CdS, II-VI such as Cu ₂ S
Group III-V compound semiconductors such as GaAs and GaAlAs are preferred materials. In particular, thin-film solar cells that use amorphous semiconductors are capable of producing larger-area films than single-crystal solar cells,
It is expected to be promising because it has advantages such as thin film thickness and deposition on any substrate material.

In the structure of an amorphous silicon solar cell, for example, when light is incident from the side opposite to the substrate, a lower electrode is provided on the substrate, and a semiconductor junction consisting of a thin p-layer, i-layer and n-layer is laminated thereon. In addition, an upper electrode is provided. Further, a grid electrode and a bus bar are provided for collecting electricity. Amorphous silicon is inferior in film quality to crystalline silicon or polycrystalline silicon and therefore has a problem of low conversion efficiency. To solve this problem, a so-called tandem cell in which two or more semiconductor junctions are stacked in series is used. Are also being considered.

By the way, when the above-mentioned solar cell is used for supplying electric power to a general household, for example, an output of about 3 KW is required. If a solar cell with a conversion efficiency of 10% is used, a large area solar cell of 30 m ² is required. However, it is difficult to produce a defect-free solar cell over a large area due to the manufacturing process of the solar cell. For example, in a polycrystal, a low resistance part is generated in the grain boundary part, or a thin film such as amorphous silicon. It is known that in a solar cell, pinholes and defects are generated due to the influence of dust during film formation of a semiconductor layer, which causes shunts and shorts, and these shunts and shorts significantly reduce conversion efficiency.

The cause of pinholes and defects and their effects will be described in more detail. For example, in the case of an amorphous silicon solar cell deposited on a stainless steel substrate, the substrate surface is not a completely smooth surface, and scratches or dents,
Alternatively, because of the presence of spike-shaped protrusions and the provision of a back reflector with unevenness for the purpose of irregularly reflecting light on the substrate, a thin semiconductor layer with a thickness of several hundred Å such as p and n layers is It is not possible to completely cover such a surface, or another cause is that pinholes are generated due to dust during film formation. The semiconductor between the lower electrode and the upper electrode of the solar cell is lost due to the pinhole, and the lower electrode and the upper electrode come into direct contact with each other, the spike-like defect of the substrate comes into contact with the upper electrode, or the semiconductor layer is removed. If the shunt or short circuit has a low resistance, if not completely lost, the current generated by light flows in parallel through the upper electrode and flows into the low resistance part of the shunt or short circuit, and the generated current is lost. If there is such a current loss, the open circuit voltage of the solar cell will drop. In particular, when the light intensity is low, the magnitude of the current generated by light and the leak current due to the shunt do not change so much, so that the drop in open circuit voltage becomes remarkable. Amorphous silicon solar cells generally require a transparent upper electrode over the entire surface of the semiconductor because the semiconductor itself has a high sheet resistance.
A conductive antireflection film such as O ₂ or ITO is provided. Therefore, even with a minute defect, the current flowing into the defect through the upper electrode becomes considerably large. Furthermore, when the defective portion is located under the grid electrode or the bus bar, the current lost due to the defective portion becomes larger.

On the other hand, at the defective portion due to the pinhole-like defect, not only the electric charge generated in the semiconductor layer leaks to the defective portion, but also an ionic substance is generated due to the interaction with moisture. At the time of use, there is a phenomenon that the electric resistance of the defective portion gradually decreases with the lapse of use time, and characteristics such as conversion efficiency deteriorate.

When a short circuit occurs as described above, the current loss can be reduced by removing or insulating the upper electrode at that location. As a method of selectively removing the upper electrode of the shunt or the short portion, there is a so-called passivation method disclosed in US Pat. No. 4,729,970, for example. This method uses AlCl ₃ , ZnCl ₂ , SnCl ₄ , SnCl ₂ , T
A solar cell and a counter electrode are dipped in a solution of a Lewis acid such as iCl _4, and a voltage is applied to change the stoichiometric ratio of the transparent conductive oxide electrode as the upper electrode, thereby increasing the resistance. is there. However, even if the upper electrode has a high resistance as described above, there is a problem that short circuit occurs again when the grid electrode is formed in the shunt portion when the grid is provided. As a measure against this, by selectively covering only the defective portion with an insulating material or a material having a high resistance sufficient to substantially prevent a shunt or a short circuit, the contact resistance with the transparent electrode, the grid electrode, or the bus bar is reduced. There is a method of increasing the conversion efficiency, and it is attracting attention as an effective means for preventing a decrease in conversion efficiency. As a specific method for selectively insulating only a defective portion of a solar cell, as disclosed in, for example, US Pat. No. 4,197,141, a polycrystalline solar cell is immersed in an electrolyte solution and an electric field is applied. There is a method of applying a voltage to oxidize a defective portion due to a polycrystal grain boundary or a lattice mismatch, or to deposit an insulator on the defective portion, or to etch the defective portion. However, according to the invention, although there is a concept of selectively depositing an insulator, it is the content of depositing an oxide of a metal such as aluminum, chromium, or copper, and the deposition of an organic polymer material is described. Not not. Further, the disclosed embodiment is an example of anodizing a defective portion of a gallium arsenide solar cell, and it is not disclosed whether a similar technique can be used for a silicon solar cell or the like.

In contrast, US Pat. No. 4,451,97
As disclosed in Japanese Unexamined Patent Publication (Kokai) No. 0, there is a method of detecting a defective portion of a solar cell with a detector and then applying an insulating material to the detected defective portion with an applicator. However, in this method, both the defect detector and the applicator are considerably large devices, and the detection is possible only in a range larger than the actual size of the defect. In addition, there is a problem in that the grid electrode cannot be printed because it rises high.
Further, since it is necessary to sweep the substrate or the applicator, there is a problem that the processing speed is slow.

[0012]

SUMMARY OF THE INVENTION In view of the above situation, an object of the present invention is to provide a defect sealing method for a solar cell which has good mass productivity and can be stably managed.

[0013]

A method for sealing defects in a solar cell according to the present invention is a method for sealing defects in a solar cell in which an electrodeposition resin is selectively deposited on a defective portion of the solar cell to insulate the defective portion. And the rate of increase in current is 10 mA /
It is characterized in that the voltage is swept so as to be not more than cm ² / sec and electrodeposition deposition is performed.

[0014]

The present invention relates to a method of selectively insulating a low resistance portion formed by a defect existing in a solar cell, which has good reproducibility and is easy to manage in a production process. The findings of the experiments conducted by the authors were completed by further detailed examination.The essence is that the electrodeposition resin is only defective when the voltage is applied by immersing the solar cell in the electrodeposition paint. The rate of increase of the flowing current is controlled so that the uniform deposition can be achieved. The current can be controlled by, for example, sweeping the voltage from a low voltage to a high voltage, and the current increasing rate is 10 mA / cm ² / sec or less. By electrodeposition at a current increasing rate of 10 mA / cm ² / sec or less, the electrodeposition on the defective portion is completed and the selectivity of electrodeposition on the defective portion is greatly improved. As a result, the electric resistance of the low resistance portion is sufficiently high, and the charge generated in the semiconductor layer is prevented from leaking to the defective portion,
The solar cell characteristics such as the conversion efficiency of the photoelectric conversion element can be significantly improved.

Further, in the solar cell manufactured by the method of the present invention, since the defective portion is insulated with the electrodeposition coating, the permeation and adsorption of water to the defective portion are strongly suppressed, and the use time that occurs during actual use may increase with time. The phenomenon of deterioration of solar cell characteristics is also greatly improved. Furthermore, in the case of a solar cell having a configuration in which a grid electrode is provided on the upper electrode, the defective portion is covered with an electrically insulating resin, so that the defective portion and the grid electrode are directly electrically connected. Shunts can also be prevented.

The defect sealing method for the solar cell of the present invention will be described below.

1 to 5 schematically show an example of the structure of a solar cell using the defect sealing method for a solar cell of the present invention.

FIG. 1 is an amorphous silicon solar cell in which light is incident from the side opposite to the substrate, FIG. 2 is a solar cell having a triple structure of the solar cell of FIG. 1, and FIG. 3 is a thin film of amorphous silicon or the like deposited on a glass substrate. Light is incident on the glass substrate from the solar cell. 4 is a crystalline solar cell, FIG. 5 is a thin-film polycrystalline solar cell, and FIG. 6 is a view of the solar cell having the configuration of FIGS. 1, 2 and 5 as seen from the light incident side. In the figure, 100 is a solar cell body, 101 is a substrate, 102 is a lower electrode, 103 is an n layer, 104 is an i layer, 105 is a p layer, 10
6 is an upper electrode, 107 is a grid electrode, 108 is a bus bar, 109 is a defective portion, and 110 is an electrodeposition resin.

The substrate 101 is a semiconductor layer 103, 104, 1 in the case of a thin film solar cell such as amorphous silicon.
05 is a member that mechanically supports and is also used as an electrode in some cases.

The lower electrode 102 is composed of the semiconductor layers 103 and 10
It is one electrode for taking out the electric power generated at 4, 105, and is required to have a work function that makes an ohmic contact with the semiconductor layer 103. As a specific material, a simple metal or an alloy, a transparent conductive oxide (TCO), or the like is used. Although the surface of the lower electrode 102 is preferably smooth, it may be textured if it causes irregular reflection of light. Also, the substrate 1
When 01 is conductive, the lower electrode 102 need not be provided. As a method for manufacturing the lower electrode 102, a known method such as plating, vapor deposition, and sputtering is preferably used.

Examples of the semiconductor layer of the solar cell used in the present invention include compound semiconductors such as pin-junction amorphous silicon, pn-junction polycrystalline silicon, and CuInSe ₂ / CdS. The semiconductor layers 103, 104, 105 and the lower electrode 102, the upper electrode 106, the grid electrode 107, the bus bar 108 and the like are formed by a generally known method.

The amorphous silicon semiconductor layer may be formed by vapor deposition, sputtering, RF plasma CVD.
Method, microwave plasma CVD method, ECR method, thermal CVD
A known method such as a method or an LPCVD method is used as desired.
As an industrially adopted method, RF plasma CVD in which a source gas is decomposed by plasma and deposited on a substrate
The method is preferred. Further, a microwave plasma CVD method which has a higher decomposition efficiency of the source gas and a higher deposition rate than the RF plasma CVD can also be used. In the case of polycrystalline silicon, C is formed by forming a sheet of molten silicon.
In the case of uInSe ₂ / CdS, it is formed by a method such as electron beam evaporation, sputtering, or deposition by electrolytic decomposition of an electrolytic solution.

As the film forming apparatus described above, a batch type apparatus or a continuous film forming apparatus can be used as desired.

The upper electrode 106 is composed of the semiconductor layers 103 and 10
The electrodes are for taking out the electromotive force generated at 4, 105 and form a pair with the lower electrode 102. Upper electrode 1
06 is required in the case of a semiconductor having a high sheet resistance such as amorphous silicon, and is not particularly necessary in a crystalline solar cell since the sheet resistance is low. Also, the upper electrode 1
Since 06 is located on the light incident side, it needs to be transparent and is also called a transparent electrode. As a method for manufacturing the upper electrode, a resistance heating vapor deposition method, an electron beam heating vapor deposition method, a sputtering method, a spray method, or the like can be used, and is appropriately selected as desired.

The grid electrode 107 is composed of the semiconductor layers 103, 1
This is an electrode for taking out the electromotive force generated at 04 and 105 and is called a collecting electrode. The grid electrode 107 is formed in a substantially skewed shape, although a suitable arrangement is determined depending on the size of the sheet resistance of the semiconductor layer 105 or the upper electrode 106, and is designed so as not to obstruct the incidence of light as much as possible.

The grid electrode is required to have a low specific resistance so as not to be a series resistance of the solar cell, and a preferable specific resistance is 10 ^-2 Ωcm to 10 ^-5 Ωcm. As the material of the grid electrode, Ti, Cr, Mo, W, Al, Ag,
Metal materials such as Ni, Cu, Sn, and Ag, Pt, C
Powder of metal such as u or C or alloy thereof is mixed with polymer binder and binder solvent at an appropriate ratio,
A so-called conductive paste in paste form is used.

As a method of forming the grid electrode 107,
Sputtering using mask pattern, resistance heating, C
VD deposition method, or method of depositing a metal layer on the entire surface and then patterning by etching, method of directly forming a grid electrode pattern by photo CVD, method of forming a negative pattern mask of the grid electrode pattern and then forming by plating There is a method of forming a conductive paste by screen printing. In the screen printing method, a conductive paste is used as a printing ink by using a screen in which a mesh made of polyester or stainless steel is subjected to desired patterning, and the electrode width can be set to about 50 μm at the minimum. . A commercially available screen printing machine is preferably used as the printing machine. The screen-printed conductive paste is heated in a drying oven to crosslink the binder and volatilize the solvent.

The bus bar 108 is an electrode for further collecting the current flowing through the grid electrode 107 at one end. As the electrode material, a metal such as Ag, Pt, Cu or the like, or a material made of C or an alloy thereof can be used, and as a form, a wire-shaped or foil-shaped material is stuck or a conductive paste similar to the grid electrode 107. May be used. As the foil-shaped material, for example, a copper foil, or a copper foil plated with tin, and an adhesive-attached material may be used in some cases. As a method of forming the bus bar 108, a metal wire may be fixed with a conductive adhesive, a copper foil may be attached, or the bus bar 108 may be formed similarly to the grid electrode 107.

The electrodeposition resin 110 is a pinhole in the semiconductor layer,
It is used to insulate a defective portion 109 due to a short-circuit or a shunt or the like caused by grain boundaries of the polycrystalline semiconductor, spike-like defects such as the substrate 101 and the lower electrode 102, and other causes. I have a match. The shunt resistance of the solar cell is ideally infinite, but 1 KΩcm ² or more is preferable, and 1
If the shunt resistance is KΩcm ² or more, the conversion efficiency of the solar cell is not affected.

It is necessary that the electrodeposition resin is directly deposited on the defective portion and is deposited on the semiconductor layer 105.
In the electrodeposition process, it is not necessary to perform electrodeposition immediately after forming the semiconductor layer 105, and electrodeposition may be performed after forming the upper electrode 106.

The deposited electrodeposited film is required to be unaffected by these treatments if there is a step of using a solvent or heat treatment after electrodeposition, depending on the method of manufacturing the solar cell. Further, the defective portion of the solar cell itself is a portion that does not contribute to power generation, but even when the electrodeposition film is selectively deposited, it is larger than the substantial area of the defective portion. Since it is considered that the electrodeposition paint is deposited on the area, it is desirable that the electrodeposition paint is a light transmissive material so as not to prevent light from entering the normal part. Considering the case of using it outdoors as a solar cell, it has good weather resistance, heat,
Stability to humidity and light is required. In addition, when the solar cell is used, the solar cell may be bent or impacted depending on the case, so it is necessary to have both mechanical strength and peel strength. The thickness of the electrodeposited coating film is such that electrical insulation and moisture resistance are maintained, and
Since it is preferable that the light transmittance is not impaired, it is appropriately selected depending on the type of resin, but typically 0.5 μm to 50 μm is suitable.

Next, the electrodeposition method of the defective portion will be described.

In the step of selectively depositing the electrodeposition resin on the defective portion, for example, the electrodeposition apparatus shown in FIG. 7 is used, and the solar cells 204 and 205 having the defective portion and the counter electrode 203 are placed in the electrodeposition coating material. It is performed by immersing and applying a voltage between the solar cell and the counter electrode 203 to deposit an electrodeposition resin on the defective portion. When a voltage is applied to the solar cell, it may be applied to the conductive substrate 204 or the lower electrode.

As the material of the counter electrode, it is required that it is not corroded in the electrodeposition coating, and platinum, carbon, which has corrosion resistance,
Nickel, stainless steel, etc. are preferably used. Also,
The area of the counter electrode is required to be a constant ratio with respect to the area of the solar cell in order to make the electrodeposition uniform. As a so-called polar ratio, the ratio of the solar cell area to the counter electrode area is 1 It is preferably in the range of / 2 to 2/1. Also,
The inter-electrode distance between the solar cell and the counter electrode is an important factor for maintaining the uniformity of electrodeposition, but there are generally suitable ranges depending on various conditions such as the electrical conductivity of the electrodeposition paint and the applied voltage. Is preferably 10 mm to 100 mm. Since the electrodeposited film is selectively deposited only on the defective portion of the solar cell, it is not preferable to expose the conductive portion such as the substrate in the electrodeposition coating. Substrate 2
04 It is desirable to cover the surface with an insulating coating material such as a plastic film or a rubber magnet. Further, when the solar cell is irradiated with light, the normal portion other than the defective portion has a low resistance due to the photovoltaic power, so that the relative ratio of the resistance value of the defective portion and the resistance value of the normal portion becomes small and the selectivity becomes low. . Therefore, if desired, the desired selectivity can be achieved by electrodeposition in the dark.

For the electrodeposition, a constant voltage method or a constant current method is generally used. In the present invention, the rate of current increase during the electrodeposition step is 10 mA / cm ² / sec or less. The voltage applied to the solar cell is a voltage equal to or higher than the hydrogen generation potential calculated from the electrode potential defined by the Nernst equation, specifically, a voltage equal to or higher than the theoretical decomposition voltage of water plus an overvoltage of 2 volts or more. A voltage is needed. Furthermore, since the preferred applied voltage range is different when the conductivity of the electrodeposition paint and the polarity of the voltage applied to the solar cell are reverse bias and forward bias, the configuration, area, and electric power of each solar cell are different. The suitable voltage range is determined from various points such as the physical properties such as the conductivity of the coating material and the polarity of the applied voltage.
It is in the range of 0V. Further, since a part of the applied voltage is also applied to the solar cell, in the case of a polarity such that the solar cell is reverse biased, a voltage within a range in which the solar cell does not break down is applied. There must be. On the other hand, when the polarity is such that it becomes a forward bias with respect to the solar cell, the forward current of the solar cell flows, resulting in poor selectivity, and in consideration of this point, the voltage must not impair the selectivity. I have to.

The current density of electrodeposition depends on the degree of shunting of the solar cell, but is 0.1 in order to form a dense electrodeposition film.
To 10 A / dm ² is a preferable range.

By the way, in the case of the constant voltage method, at the initial stage of electrodeposition, the defect portion has a low resistance, so that the speed of electrodeposition is high and a large current flows, but thereafter, the deposited electrodeposition film has a high resistance, so that the current Is significantly reduced. Such a large fluctuation of the current is difficult to adopt because it affects the stability of the conditions in production. On the other hand, when the constant current method is used to solve this problem, the current is always constant, so the deposition rate of the electrodeposition film is constant, and in this respect, a dense electrodeposition film is formed. . However, since the voltage rises gradually, it is necessary to control the voltage to be equal to or lower than the breakdown voltage when the polarity is such that a reverse bias is applied to the solar cell. This is also a problem in production. The defect sealing method for a solar cell according to the present invention does not cause the above-mentioned problems because the current and voltage flowing during electrodeposition do not rise or fall sharply. Specifically, a method of gradually increasing the voltage and holding it at a constant voltage is used.

As a method for determining the end point of electrodeposition, a method based on time, a method based on Coulomb amount, etc. can be used. Since the electrodeposition film has a high resistance, when the film thickness reaches a certain value, no film is formed on that part.Therefore, depending on the configuration of the solar cell, electrodeposition will automatically end when a defective part is deposited. It is also possible that the current stops flowing. However, in the case where a forward bias is applied to the solar cell, even if there is selectivity at the initial stage of electrodeposition, deposition also occurs in a normal portion with the passage of time. It is necessary to manage the electrodeposition end point by the amount.

The electrodeposition coating material 202 is prepared by dispersing an electrodeposition resin in a solvent at a predetermined concentration and adjusting it to a predetermined electric conductivity.

The electrodeposition resin has insulation and moisture resistance, and the skeleton resin is acrylic resin, polyester resin, epoxy resin, urethane resin, fluorine resin, melamine resin, butadiene resin, or the like, if desired. Is appropriately selected. Further, it is necessary to introduce a functional group capable of causing ionization in a solution in order to dissolve these resins and perform electrophoresis, and the functional group includes a carboxyl group, an amino group and the like. The electrodeposition paint can be classified into a cationic type and an anionic type depending on the polarity of the functional group. Each,
Since the polarities applied to the solar cells are different, they may be appropriately selected according to the desired polarities of the solar cells. Further, in order to cure the electrodeposition resin by heating, since a melamine crosslink, a carbon-carbon double bond, a urethane bond, etc. are used, a functional group capable of causing these crosslinking reactions is appropriately introduced into the skeleton resin or the side chain. The electrodeposition resin needs to be formed only on the defective portion of the solar cell, and for this purpose, unnecessary paint should be easily washed after electrodeposition. The MFT) is preferably 50 ° C or higher.

In order to form a uniform film, it is important that these electrodeposition resins do not precipitate in the solution and are stably suspended. For this purpose, it is desirable that the resin be colloidal particles having an appropriate size. The particle size of colloidal particles is
The range of 10 nm to 100 nm is desirable, and the particle size is preferably monodisperse. The weight average molecular weight of the skeleton resin constituting the colloidal particles is preferably about 1,000 to 20,000. It is also possible to disperse a filler such as an inorganic pigment, ceramics, glass frit or fine particle polymer in the electrodeposition resin in order to improve light resistance, heat resistance, moisture resistance, selectivity of defective portion, etc. To use. In order to selectively and effectively insulate the defective portion of the solar cell, it is preferable that the weight of the electrodeposition film per unit amount of electricity is large. For this purpose, the Coulomb efficiency of the electrodeposition coating is preferably 10 mg / C or more. As the solvent of the electrodeposition paint, a solution containing a transparent conductive oxide, a concentration of an acid or alkali that does not easily dissolve the solar cell constituent materials such as the semiconductor layer and the lower electrode, or a solution containing a metal salt thereof is used. . As the metal salt, a salt having a negative standard electrode potential and a hydrogen overvoltage smaller than the absolute value of the standard electrode potential is used as the metal constituting the salt. The electrodeposition coating composition is diluted with deionized water for use, and the range of good film-forming property is preferably in the range of 1% to 25% in solid content. Further, the conductivity of the electrodeposition liquid is preferably in the range of 100 μS / cm to 2000 μS / cm so that the resin is stably suspended, electrophoresis is likely to occur, and deposition is likely to occur at a desired defect portion.

The desirable mode of the defect sealing method of the solar cell of the present invention is not only the method of electrodepositing the defective portion, but also the method of removing the upper electrode of the low resistance portion by passivation and electrodepositing the latent defect. Also, a method of removing the upper electrode of the exposed defect portion and performing electrodeposition after a forming process for exposing the surface is included.

Further, the electrodeposition may be carried out after the formation of the upper electrode or before the formation of the upper electrode, which is appropriately selected depending on the structure of the solar cell. In the case of the latter method, the number of manufacturing steps can be reduced as compared with the former method, because the passivation is unnecessary. On the other hand, after forming a semiconductor film by a vacuum process, it is necessary to perform electrodeposition of a wet process and further to sufficiently dry water for forming an upper electrode by a vacuum process.

In the above description, the solar cell is in the form of a cut sheet, and the electrodeposition process is single-wafer processing.
Roll-to-roll can be used if necessary. An apparatus suitable for roll-to-roll processing is shown in FIG.
In FIG. 8, reference numeral 310 is a substrate, 301 is a substrate delivery roller, 302 is a substrate winding roller, 303 is an electrolytic bath, 304 is a cleaning bath, 305 is a drying oven, 306 is a power supply,
Reference numeral 307 is a mask film feeding roller, 308 is a mask film winding roller, 309 is a mask film, 311 is a counter electrode, and 312 is a conductive roller.

As a preferred embodiment in this figure, the solar cell is nip type amorphous silicon deposited on a stainless steel substrate, and an ITO upper electrode is formed on the light incident side. The solar cell substrate 310 is delivered from the delivery roll 301 and immersed in the electrolytic bath 303,
After passing through the cleaning tank 304 and the drying furnace 305, it is taken up by the take-up roll 302. Before being immersed in the electrolytic bath 303, a film 309 for a solar cell backside mask is sent out from the mask film sending-out roller 307 and bonded to the backside of the solar cell substrate 310. After the electrodeposition is completed, it is peeled off again, washed, dried, and then wound around the winding roller 308. The conductive roller 312 in contact with the solar cell substrate 310 and the counter electrode 31 immersed in the electrolytic cell 303.
During 1, the voltage of the power supply 306 is applied.

The solar cell produced as described above is modularized by encapsulation by a known method in order to further improve weather resistance and maintain mechanical strength when used outdoors. Specifically, as an encapsulation material, for the adhesive layer, adhesiveness with a solar cell,
EVA (ethylene vinyl acetate) is preferably used in terms of weather resistance and buffering effect. Further, in order to further improve the moisture resistance and the scratch resistance, a fluorine resin is laminated as the surface protective layer. Examples of the fluorine-based resin include tetrafluoroethylene polymer TFE (Teflon manufactured by DuPont, etc.), tetrafluoroethylene / ethylene copolymer ETFE.
(DuPont Tefzel, etc.), polyvinyl fluoride (DuPont Tedlar, etc.), polychlorofluoroethylene C
TFE (Neotron manufactured by Daikin Industries) and the like can be mentioned.
The weather resistance may be improved by adding an ultraviolet absorber to these resins. As a method of encapsulation, it is desirable to use a commercially available device such as a vacuum laminator to heat and pressure bond the solar cell substrate and the resin film in vacuum.

[0047]

EXAMPLES Hereinafter, the method of sealing defects in a solar cell of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A solar cell 100 having the layer structure shown in FIG. 1 was produced as follows. First, a substrate made of SUS430BA that has been thoroughly degreased and washed (30 cm x
(30 cm, thickness 0.2 mm) 101 is put in a DC sputtering device (not shown) to deposit 2000 liters of Cr, and the lower electrode 10
Formed 2. The substrate 101 is taken out and put in an RF plasma CVD film forming apparatus (not shown), and the n layer 103, i layer 104,
Deposition was performed in order of the p layer 105. Then, it is placed in a resistance heating vapor deposition device (not shown) and 1 × 10 5 is introduced while introducing oxygen.
^While maintaining an internal pressure of ^-4 Torr, an alloy of In and Sn was vapor-deposited by resistance heating, and a transparent ITO upper electrode 106 having an antireflection effect was deposited 700 Å.

Next, the back surface side of the substrate 101 was covered with an insulating film made of plastic so that the back surface of the substrate 101 was not electrodeposited during electrodeposition, and the substrate was immersed in the electrolytic bath 201 of FIG. As the counter electrode 203, a SUS304 stainless steel plate having a size of 30 cm × 30 cm so that the polar ratio was 1: 1 and the back side of which was sealed with a plastic insulating film with respect to the substrate 101 was used. As the electrodeposition paint 202, an acrylic anion electrodeposition paint having a solid content of 10% was used. A positive voltage was swept on the substrate 204 from 0 V to 10 V in 15 seconds, and after reaching 10 V, it was held for 60 seconds for electrodeposition. The voltage-time curve and the current one-hour curve at this time are shown in FIG. As shown in the figure, the rate of increase of the current value is 10 mA / cm ² / sec or less, and it can be seen that the current value does not change rapidly within the electrodeposition time.

Next, the substrate 204 is pulled up from the electrolytic bath 201, thoroughly washed with pure water, the unreacted electrodeposition paint is washed off, placed in an oven at 50 ° C. and left for 30 minutes to dry the water. It was Then, the temperature of the oven was raised at a rate of 10 ° C./minute, and after reaching 180 ° C., the temperature was kept for 30 minutes to cure the electrodeposition resin. This sample was It was set to 1-1.

After that, the sample No. When 1-1 was taken out of the oven and cooled, a part of it was cut out and observed with a scanning electron microscope.
Hemispherical deposits 110 having a diameter of 50 μm were scattered and observed. When the infrared absorption of this portion was analyzed by using FTIR with a microscopic function, it was confirmed that there was carbonyl group absorption and the electrodeposition coating material was deposited. Further, when the OBIC image of this sample was observed, it was confirmed that only the deposited portion of the electrodeposition coating did not generate power, and therefore the deposited film was deposited only on the shunt portion. Furthermore, the area where the electrodeposition resin was deposited was 10 times or less the area of the shunt portion, and there was almost no deposition of the electrodeposition film on the unnecessary portion.

Next, sample No. After sticking the mask film on 1-1, IT with ferric chloride and hydrochloric acid etchant
O was etched to form 100 subcells each having a size of 1 cm ² at equal intervals. Then, it was put into an EB vaporizer (not shown) to form a chromium electrode having a size of 1 cm ² on the subcell. FIG. 10 shows the result of measuring the reverse bias withstand voltage of the solar cell by applying a reverse bias to the subcell formed as described above. In the figure, the vertical axis is an arbitrary scale. It is considered that the case where the reverse bias withstand voltage is low indicates that the shunt-prone portion remains. Figure 1
In the case of 0, the reverse bias withstand voltage is about −10 V, which shows that the low resistance portion is insulated by the electrodeposition process and has a good withstand voltage characteristic.

Next, for comparison, the defect sealing of the solar cell was performed in substantially the same manner as described above except that the electrodeposition was performed at a constant voltage.

The upper electrode 106 was formed on the substrate 101 in the same manner as described above, and then the voltage was maintained at 10 V and electrodeposition was performed for 60 seconds. The voltage-time curve and the current-time curve at this time are shown in FIG. As shown in the figure, the current drastically flows at the initial stage of electrodeposition and then sharply decreases. The initial rate of increase in current was 10 mA / cm ² / sec or more. Then, in the same manner as described above, the chrome electrode was formed by separating into subcells.

Further, a reverse bias was applied and the reverse bias breakdown voltage was measured. Results are shown in FIG. As is clear from the comparison between FIG. 10 and FIG. 12, the reverse bias withstand voltage of the solar cell is increased and the low resistance portion is effective when the rate of increase of the current value during electrodeposition is 10 mA / cm ² / sec or less. It turned out to be insulated.

Next, ten solar cells shown in FIG. 1 were prepared by the voltage sweep method shown in FIG. 9, and then the substrate 101 was placed on a screen printing machine (not shown) to form a grid electrode 108 having a width of 100 μm and a length of 8 cm. Were printed at intervals of 1 cm. At this time, the conductive paste used had a composition containing 70 parts of Ag filler, 30 parts of polyester binder (volume ratio), and 20 parts of ethyl acetate as a solvent. After printing, the substrate 101 was put in an oven and kept at 150 ° C. for 30 minutes to cure the conductive paste. Further, a bus bar 109 of copper foil with an adhesive having a width of 5 mm was adhered to produce a 30 cm square single cell shown in FIG.

Next, encapsulation of these samples was performed as follows. EVA is laminated on the upper and lower sides of the substrate 101, and the fluororesin film ETFE is formed on the upper and lower sides of the EVA.
After stacking (ethylene tetrafluoroethylene) (Tefzel made by DuPont), put it in a vacuum laminator and
Hold at 0 ° C. for 60 minutes to carry out vacuum lamination.
These samples are 1-2 to No. It was set to 1-11.

Next, for comparison, a solar cell without electrodeposition was prepared as follows.

First, the upper electrode 106 was formed on the substrate 101. Next, in the same manner as described above, the grid electrode 10
7 was printed. Furthermore, copper foil with adhesive is used for the bus bar 10
8 were laminated, and 10 single cells of 30 cm square shown in FIG. 6 were produced.

Next, encapsulation of this sample was performed in the same manner as described above. The obtained sample was analyzed by R. 1-1 to R.I. It was set to 1-10.

The above sample No. 1-2 to No. 1-1
1 and comparative sample R.I. 1-1 to R.I. The initial characteristics of 1-10 were measured as follows.

First, the voltage-current characteristics of the sample in the dark state were measured, and the shunt resistance was obtained from the slope near the origin. Then 100 in the AM1.5 global solar spectrum
The solar cell characteristics were measured using a pseudo solar light source (hereinafter referred to as a simulator) having a light amount of mW / cm ² , and the conversion efficiency was obtained. The results are shown in FIGS. 13 and 14. Sample N
o. 1-11 to No. 1-20 is a comparative sample R.I. 1-1
To R. It can be seen that the average value is high and the variation is small as compared with 1-10.

The reliability test of these samples was carried out by the temperature and humidity cycle test A specified in the environmental test method and the durability test method of the crystalline solar cell module of Japanese Industrial Standard C8917.
-2.

First, the sample is placed in a thermo-hygrostat whose temperature and humidity can be controlled, and from -40 ° C to + 85 ° C (85% relative humidity).
The cycle test of changing to 10 was repeated 10 times. Next, the solar cell characteristics of the sample after the test were measured using a simulator as in the initial stage. The results are shown in FIGS. 13 and 14. As shown in the figure, the sample of this example had better initial conversion efficiency and shunt resistance than the comparative sample.

From the results of this example, it is understood that the solar cell manufactured by using the defect sealing method for a solar cell of the present invention has good yield, good characteristics, and high reliability.

(Example 2) A solar cell was prepared as follows by a method substantially similar to that of Example 1 except that the solar cell shown in FIG. 2 was used as the solar cell.

First, a lower electrode 102 consisting of an AlSi layer having a texture structure and a ZnO layer as a high resistance transparent conductive member for shunt prevention is formed on a substrate 101, and then a microwave plasma CVD film formation (not shown) is formed. The bottom layer was formed by depositing the n layer 103, the i layer 104, and the p layer 105 in this order in the apparatus. At this time, the i layer 104 is a-SiG
e. Next, the n layer 113, the i layer 114, and the p layer 115 were deposited in this order to form a middle layer. The i layer 114 was made of a-SiGe similarly to the bottom layer. Next, the n-layer 123, i
A layer 124 and a p layer 125 were deposited in this order to form a top layer. The i layer 124 was a-Si. Next, as in Example 1, the transparent upper electrode 106 having an antireflection effect
00Å deposited. As the upper electrode 106, In ₂ O ₃ (I
O) was used.

Next, an electrodeposition process was performed using the fluorine-based anion electrodeposition coating material 202 in the electrolytic cell 201 of FIG. Fig. 15 shows the waveform of the voltage and the curve of current and time during electrodeposition. As shown in the figure, in this embodiment, the voltage is set to 10 for 30 seconds.
It was raised to V and then lowered to 0 V in 30 seconds. Then, the electrodeposition liquid was washed and cured. The grid electrode 107 is printed, and the bus bar 108 is further laminated thereon, as shown in FIG.
A cm square triple cell was prepared. Similarly, ten samples were prepared.

Further, the encapsulation of this sample was performed in the same manner as in Example 1. The obtained sample was Two
-1 to No. It was set to 2-10.

For comparison, a sample prepared by the same method as described above except that no electrodeposition was carried out was used.
2-1 to R.I. It was set to 2-10.

Sample No. 2-1 to No. The initial characteristics of Comparative Sample R. 2-1 to R.I. 16 and 17 in comparison with 2-10.

Next, a reliability test of this sample was conducted in the same manner as in Example 1, and the results are shown in FIGS.

As is clear from the figure, it was shown that by using the defect sealing method of the present invention, a solar cell having good initial characteristics and high reliability can be manufactured.

(Example 3) A solar cell of Fig. 1 was prepared as follows, in substantially the same manner as in Example 1 except that the electrodeposition coating was a cationic electrodeposition coating. First, the upper electrode 106 was formed using a film forming apparatus (not shown).

Next, an electrodeposition treatment was performed in the electrolytic bath 201 of FIG. 7 using the epoxy-based cationic electrodeposition coating material 202. FIG. 18 shows the voltage-time waveform and the current-time curve during electrodeposition. As shown in the figure, the trapezoidal voltage sweep method was used.
After the electrodeposition was completed, it was washed and cured. Grid electrode 107
Was printed, and the bus bar 108 was further laminated to produce a 30 cm square triple cell shown in FIG. Similarly 10
A sample was prepared.

Further, the encapsulation of this sample was carried out in the same manner as in Example 1. The obtained sample was Three
-1 to No. It was set to 3-10.

For comparison, a sample which was not subjected to electrodeposition was prepared in the same manner as in Example 1, and the obtained sample was used as Comparative Sample R. 3-1
To R. It was set to 3-10.

Sample No. 3-1 to No. The initial characteristics of the comparative sample R. 3-1 to R.I. 19 and 20 as compared with 3-10.

Next, the reliability test of this sample was conducted in the same manner as in Example 1, and the results are shown in FIGS. 19 and 20. As shown in the figure, it was shown that the defect sealing method of the present invention can manufacture a solar cell having good initial characteristics and high reliability.

Example 4 Next, a solar cell 100 having the structure shown in FIG. 1 was produced in substantially the same manner as in Example 1 except that the electrodeposition was performed after the formation of the p layer 105.

As in Example 1, the lower electrode 102 was formed on the substrate 101 made of SUS430BA, and the n layer 103, the i layer 104, and the p layer 1 were formed by an RF plasma CVD film forming apparatus (not shown).
Deposition was performed in the order of 05.

Next, as in the first embodiment, the substrate 101 described above is used.
The back side of was covered with an insulating film made of plastic and immersed in the electrolytic cell 201 of FIG. Electrodeposition treatment was performed using the styrene-based anion electrodeposition coating material 202. Voltage at this time −
The time waveform and the current-time curve are shown in FIG. In the present invention, the voltage is a triangular wave. Then, as in Example 1, a transparent upper electrode 106 having a function also serving as an antireflection effect, a grid electrode 107, and a bus bar 108 were laminated to produce a 30 cm square single cell shown in FIG.
Similarly, ten samples were prepared.

Further, the encapsulation of this sample was performed in the same manner as in Example 1. The obtained sample was Four
-1 to No. It was set to 4-10.

For comparison, a sample obtained by preparing a sample without electrodeposition in the same manner as described above was used as a comparative sample R.I. 4-1 to R.I. It was set to 4-10.

The initial characteristics and shunt resistance of the obtained sample are shown in FIGS. 22 and 23.

Next, the durability characteristics of this sample were evaluated in the same manner as in Example 1, and the results are shown in FIGS. 22 and 23.

From the results of this example, it is understood that the solar cell of the present invention manufactured by using the defect sealing method for a solar cell of the present invention has good yield, good characteristics, and good durability.

[0088]

The solar cell is immersed in the electrodeposition coating material, and the voltage is swept and applied so that the increasing rate of the current is 10 mA / cm ² / sec or less. It becomes possible to deposit the resin and insulate the defective portion.

That is, the defect sealing method for a solar cell according to the present invention enables defect sealing that is easy to manage, and it is possible to provide a solar cell with a high yield and high reliability.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a solar cell of the present invention.

FIG. 2 is a schematic diagram showing the configuration of the solar cell of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a solar cell of the present invention.

FIG. 4 is a schematic diagram showing the configuration of the solar cell of the present invention.

FIG. 5 is a schematic diagram showing the configuration of the solar cell of the present invention.

FIG. 6 is a schematic diagram showing a configuration of a solar cell of the present invention.

FIG. 7 is a schematic view showing a single-wafer electrodeposition apparatus.

FIG. 8 is a schematic view showing a roll-to-roll type electrodeposition apparatus.

FIG. 9 is a diagram showing voltage-time and current-time curves during electrodeposition.

FIG. 10 is a graph showing a distribution of breakdown voltage of a solar cell manufactured by the defect sealing method of the present invention.

FIG. 11 is a graph showing voltage-time and current-time curves during electrodeposition in a conventional example.

FIG. 12 is a graph showing a breakdown voltage distribution of a solar cell manufactured by a defect sealing method of a conventional example.

FIG. 13 is a diagram showing conversion efficiency in the initial stage and after the reliability test.

FIG. 14 is a diagram showing shunt resistance in the initial stage and after a reliability test.

FIG. 15 is a diagram showing voltage-time and current-time curves during electrodeposition.

FIG. 16 is a diagram showing conversion efficiency in the initial stage and after the reliability test.

FIG. 17 is a diagram showing the shunt resistance in the initial stage and after the reliability test.

FIG. 18 is a diagram showing voltage-time and current-time curves during electrodeposition.

FIG. 19 is a diagram showing conversion efficiency in the initial stage and after the reliability test.

FIG. 20 is a diagram showing shunt resistance in the initial stage and after a reliability test.

FIG. 21 is a diagram showing voltage-time and current-time curves during electrodeposition.

FIG. 22 is a diagram showing conversion efficiency in the initial stage and after the reliability test.

FIG. 23 is a diagram showing the shunt resistance in the initial stage and after the reliability test.

[Explanation of symbols]

 100 solar cell main body 101 substrate 102 lower electrode 103, 113, 123 n layer 104, 114, 124 i layer 105, 115, 125 p layer 106 upper electrode 107 grid electrode 108 bus bar 109 defective portion 110 electrodeposition film 201 electrolytic cell 202 electrolysis Liquid 203 Counter electrode 204 Substrate 205 Semiconductor layer 206 Power supply 207 Conductive wire 301 Substrate delivery roller 302 Substrate take-up roller 303 Electrolytic bath 304 Cleaning bath 305 Drying oven 306 Power supply 307 Mask film delivery roller 308 Mask film take-up roller 309 Mask film 310 Substrate 311 Counter electrode 312 Conductive roller.

Front Page Continuation (72) Inventor Takahiro Mori 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Soichiro Kawakami 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. A defect sealing method for a solar cell, wherein an electrodeposition resin is selectively deposited on a defect portion of the solar cell to insulate the defect portion, wherein the electrodeposition resin has a current increasing rate of 10 mA.
A method for sealing defects in a solar cell, characterized in that the voltage is swept so as to be not more than 1 / cm ² / sec and electrodeposition deposition is performed.