TW201515244A - Solar cell and solar cell module - Google Patents

Abstract

Provided is a solar cell having a back surface structure that minimizes carrier recombination loss at the non-acceptance surface, and that affords good electrical contact between the collector electrode and the crystalline silicon substrate. The solar cell is provided with a crystalline silicon substrate having a first conduction type, an emitter layer formed on the crystalline silicon substrate and having a second conduction type, and a base layer formed on the crystalline silicon substrate and having the first conduction type, electrodes for extracting to the outside the charges excited by light impinging on the substrate being respectively formed on the emitter layer and the base layer, wherein a protruding and recessed structure having a plurality of protrusions and recesses is furnished to a region that is at least part of the electrode formation region of the non-acceptance surface.

Description

Solar battery and solar battery module

The present invention relates to a solar cell having a back surface structure excellent in passivation and having good electrical contact between the collector and the crystalline germanium substrate.

Fig. 1 is a schematic view showing a general solar cell using a single crystal or polycrystalline germanium substrate. A concave-convex structure 102 for confining light is formed on the light-receiving surface of the first-conductivity-type crystalline germanium substrate 101. The uneven structure 102 is obtained by immersing the substrate 101 in an acidic or alkaline solution for a certain period of time. In the acidic solution, a mixed acid solution of acetic acid, phosphoric acid, sulfuric acid, water, or the like is mixed with the hydrofluoric acid nitric acid. When the substrate 101 is immersed in this case, the fine grooves on the rough surface during the processing of the substrate are preferentially etched or the like to form a concavo-convex structure. Further, as the alkali solution, calcium hydroxide or an aqueous sodium hydroxide solution or an aqueous solution of tetramethylammonium hydroxide is used. Since the etching is performed by forming the Si-OH coupling by the alkali etching, the etching speed depends on the crystal plane orientation, and thus the uneven structure in which the etching speed is slow is obtained.

Further, a conductive type emitter layer 103 opposite to the first conductivity type is formed on the light receiving surface of the substrate 101. The first conductivity type mainly uses a p-type germanium substrate to which a group III element such as B is added, and one of the emitter layers 103 is used. It is formed by thermally diffusing a group V element such as P.

Further, a protective film 104 is formed on the emitter layer 103 so as to cover the emitter layer 103. The protective film 104 has the following two functions.

The first one is used as a reflection preventing film for maximally taking light incident on the solar cell, and a dielectric body having a refractive index smaller than that of crystallization and larger than air is used. Specifically, titanium oxide, tantalum nitride, tantalum carbide, hafnium oxide, aluminum oxide, or the like may be used. These film thicknesses differ depending on the refractive index of the film. In the case of a tantalum nitride film, in general, The light receiving surface is about 80 to 100 nm.

The second effect is the carrier suppression of the surface of the crucible. It has a passivation effect on the defect terminal of the surface of the substrate on which the light-generated carrier is destroyed. The atoms adjacent to the ruthenium atom in the crystal are covalently bonded to each other to form a stable state. However, due to the absence of bound adjacent atoms at the surface of the end of the atomic arrangement, unstable energy levels known as unbound or dangling bonds occur. Because of the electrical activity, the dangling bond captures the charge generated by the light inside the crucible and is destroyed, and the characteristics of the solar cell are impaired. In order to suppress the loss, the dangling bond is lowered in the solar cell by applying some surface termination treatment, or the antireflection film holds the electric charge, thereby greatly reducing any of the electrons or holes in the surface. The concentration that inhibits the recombination of electrons and holes. In particular, the latter is called field effect passivation. It is known that a tantalum nitride film or the like holds a positive charge, and field effect passivation is known.

Then, the protective film 104 is passed through the emitter layer 103 to form an electrode 105 for extracting a carrier generated by light. The formation of the electrode In the method, a method in which a metal paste of a metal fine particle such as silver is mixed with an organic binder by printing such as screen printing and heat-treated to be bonded to a substrate is widely used. Electrode formation is generally performed after formation of a dielectric film. Therefore, in order to bring the electrode into contact with the crucible, it is necessary to remove the dielectric film between the electrode and the crucible, and by adjusting the glass component or the additive in the metal paste, the metal paste can be passed through the protective film 104 to be in contact with the crucible. .

Further, the non-light-receiving surface on the opposite side of the light-receiving surface forms a base layer 106 of a conductive type impurity having the same concentration as that of the substrate 101 in order to suppress the recombination of the carriers for generating light, and to cover the base layer 106. In this manner, the electrode 107 is formed.

In terms of the formation method of the base layer 106, from the viewpoint of cost, generally, the above-mentioned p-type ruthenium substrate is printed with an aluminum paste mixed with aluminum microparticles in an organic binder using a screen or the like, and a eutectic point of lanthanum and aluminum. A method of heat treatment at a temperature of (577 ° C) or more. When the heat treatment is performed at this temperature, lanthanum is ingested more aluminum during recrystallization and recrystallized to form a base layer. Further, during the above heat treatment and recrystallization, most of the aluminum paste remaining at the interface with the tantalum contact remains, and becomes the electrode 107.

On the other hand, in the base layer-electrode structure using aluminum, the effect of suppressing the carrier recombination on the back surface of the solar cell is limited, and the absorption coefficient of light is large, which causes a problem of large optical loss.

Then, in order to avoid these problems and to increase the efficiency of the solar cell, a so-called PR (Passivated Rear) structure type solar cell shown in Fig. 2 has been proposed. The PR structure is characterized by having a non-light-receiving surface of the substrate 201 The planarization is performed, and the protective film 207 having a high passivation effect is covered, and the base layer 206 and the electrode 208 are localized to reduce the surface recombination of the carrier.

Further, 201 is a substrate, 202 is a embossing, 203 is an emitter layer, 204 is a protective film, and 205 is an electrode.

In the method of forming the uneven structure on the light-receiving surface and smoothing the non-light-receiving surface, the ruthenium substrate after the dicing process is immersed in an alkali or an acid solution to perform damage etching, and then only the light-receiving surface is exposed to the reactive ions. Or a method of forming a concavo-convex structure by etching a gas, or immersing the substrate after the damage etching in an alkali or an acid solution to form an uneven structure on both surfaces of the substrate, and then using a rotary etcher or a belt-type etching device to the non-light-receiving surface A method of performing wet etching on a concavo-convex structure.

Further, in the method of partially forming the base layer or the electrode, a protective film is formed by patterning such as photolithography or etching paste, and an opening is provided, and impurities are added to the opening by thermal diffusion or the like, and then by A method of forming a metal such as Al or Ag on the base layer by physical vapor deposition (Non-Patent Document 1).

[prior technical literature] [Patent Document]

[Non-patent literature] J. Knobloch, et. al., IEEE PVSC, pp.271~276, 1993.

However, in the above-described manner, it is easy to obtain high conductivity and adhesion by electrodes which are physically vapor-deposited. Conversely, since the raw material utilization rate is low on the production surface and the engineering is complicated, there is a problem that the cost becomes high. Therefore, even in the formation of the PR structure, by using an electrode such as a metal paste similar to the electrode 105 of FIG. 1, it is necessary to reduce the cost.

The present inventors have created the present invention in view of the above and meticulously studied the results. That is, the present invention provides the following solar cell.

In other words, the solar cell according to the embodiment of the present invention includes: a crystalline germanium substrate having a first conductivity type; and an emitter layer having a second conductivity type formed on the crystalline germanium substrate, and being formed on the crystalline germanium substrate. a base layer having a first conductivity type, wherein an electrode for extracting electric charges excited by light incident on the substrate to the outside is formed in the emitter layer and the base layer, and at least a part of the region where the electrode is formed in the substrate is formed. It has a concave-convex structure with a plurality of irregularities.

Even if at least one of the electrodes is formed on the non-light-receiving surface of the substrate, at least a part of the non-light-receiving surface other than the region where the electrode is formed may be smoother than the uneven structure. In addition, the height difference between the concave portion and the convex portion in the uneven structure may be 0.5 μm or more. Furthermore, even if the electrode is a sintered body of metal particles and glass.

A solar battery module according to an embodiment of the present invention is configured by electrically connecting the solar cells.

According to the present invention, it is possible to form a high-quality PR structure easily and inexpensively on the back surface of the solar cell, and it is extremely effective for increasing the efficiency and cutting costs of the solar cell.

101, 201, 301, 401‧‧‧ substrates

102, 202, 302, 402‧‧

103, 203, 303, 403‧‧ ‧ the emitter layer

305, 405‧‧‧ concave and convex structure

104, 204, 207, 306, 307, 406, 407‧‧ ‧ protective film

105, 107, 205, 208, 308, 309, 408, 409‧‧‧ electrodes

106, 206, 304, 404‧‧‧ base layer

Fig. 1 is a view showing an example of a structure of a general solar battery by a prior art.

Fig. 2 is a view showing another example of the structure of a general solar cell by the prior art.

Fig. 3 is a view showing the configuration of a solar cell relating to the present invention.

Fig. 4 is a view showing a modification of the structure of the solar cell according to the present invention.

Fig. 5 is a graph showing the influence of the height difference of the uneven structure on the contact resistance of the electrode.

An example of a method of manufacturing a solar cell of the present invention will be described below with reference to Fig. 3 . However, the present invention is not limited to the solar cell produced by the method.

Use a high concentration alkali such as sodium hydroxide or calcium hydroxide at a concentration of 5 to 60%, or a mixed acid of hydrofluoric acid and nitric acid, etc., and etch it in a high-purity antimony-doped phosphorus or arsenic or antimony-like V group element and the resistivity is set. It is 0.1~5Ω. Cm original The slice damage of the surface of the n-type crystalline germanium substrate is cut. The crystal ruthenium substrate may be produced by a method such as a casting method, a Cz method or an FZ method.

Next, a scribe 302 for optical confinement is formed on the substrate 301. The engraving 302 is made by immersing in an alkali solution of heated sodium hydroxide, calcium hydroxide, calcium carbonate, sodium carbonate, sodium hydrogencarbonate or tetramethylammonium hydroxide (concentration: 1 to 10%, temperature: 60 to 100 ° C) It is easy to make in 10 minutes to 30 minutes. In the above solution, a specific amount of 2-propanol was dissolved, and the reaction was controlled to be large. When this method is applied to a single crystal germanium substrate having a crystal plane orientation of <100>, a so-called random pyramid structure in which a plane direction <111> is mostly exposed in a pyramid shape is obtained. Further, when the crystal plane orientation is a random polycrystalline germanium substrate, since the random pyramid cannot be uniformly formed, it is possible to apply, for example, H ₂ or CHF ₃ , SF ₆ , CF by high frequency at a pressure of about 1 to 20 Pa. _4. A method of etching a ruthenium by a reactive ion of a gas such as C ₂ F ₆ , C ₃ F ₈ or ClF ₃ , more preferably a method of immersing the substrate in an acidic mixed solution of hydrogen fluoride, nitric acid, acetic acid or phosphoric acid. For a more specific method of acid etching in the latter, a mixed solution of, for example, 15 to 31% by weight of nitric acid and 10 to 22% by weight of hydrofluoric acid is used. More preferably, the acetic acid is mixed by 10 to 50 w% to the above mixed acid solution. The liquid temperature is set to 5 to 30 ° C, and the crucible substrate is immersed for about 10 minutes to 30 minutes, whereby an isotropic embossed structure having an arc-shaped cross section can be easily obtained.

Next, an emitter layer 303 is formed. It is generally suitable to use BBr ₃ containing a boron gas to diffuse boron to the substrate by vapor phase diffusion at 800 to 1000 ° C. Furthermore, it is not limited to this, and even a boron compound which can be screen-printed or spin-coated can be used. The emitter layer 303 must be formed only on the light-receiving surface. In order to achieve this, it is necessary to perform processing such as diffusion in a state in which the two non-light-receiving surfaces are overlapped face-to-face, or diffusion of tantalum nitride or the like on the non-light-receiving surface. The barrier is such that the added impurities do not diffuse to the non-light-receiving surface.

The boron concentration on the surface of the emitter layer 303 is preferably 1 × 10 ¹⁹ or more and 3 × 10 ²⁰ atoms/cm ^{3 , more} preferably about 5 × 10 ¹⁹ or more and 1 × 10 ²⁰ atoms / cm ³ . When it is less than 1 × 10 ¹⁹ atoms/cm ³ , the contact resistance between the substrate and the electrode becomes large, and when it is set to 3 × 10 ²⁰ atoms/cm ³ or more, the defect in the emitter layer and the Auger composite The combination of the charge carriers caused by (Auger recombination) is obvious, and the output of the solar cell is lowered. After the diffusion, the glass produced on the surface is removed with hydrofluoric acid or the like.

Next, a base layer 304 is formed. It is generally suitable to use POCl ₃ to diffuse phosphorus into the substrate by vapor phase diffusion at 900 to 1100 ° C. Furthermore, it is not limited to this, and even a phosphorus compound which can be screen-printed or spin-coated can be used. In general, the solar cell must form the base layer 304 only on the non-light-receiving surface. In order to achieve this, it is necessary to perform processing such that two sheets are overlapped in a state in which the light-receiving surfaces of the two substrates face each other to be diffused, or on the light-receiving surface. A diffusion barrier such as tantalum nitride is formed on the side so that phosphorus does not diffuse to the light receiving surface.

The surface phosphorus concentration of the base layer 304 is preferably 1×10 ¹⁹ or more and 1×10 ²¹ atoms/cm ^{3 in} order to obtain good electrical contact between the substrate and the electrode, and is set to be 5×10 ¹⁹ or more and 1×10. The degree of ²¹ atoms/cm ³ or less is more preferable. When it is less than 1 × 10 ¹⁹ atoms/cm ³ , the contact resistance between the substrate and the electrode becomes large, and the output of the solar cell decreases. 1 × 10 ²¹ atoms / cm ³ is the approximate solid solution limit of phosphorus to ruthenium. After the diffusion, the glass produced on the surface is removed with hydrofluoric acid or the like.

Next, a concavo-convex structure 305 is formed in the electrode formation region. The concavo-convex structure 305 can be applied to, for example, the same as the engraving 302 formed on the light receiving surface. Here, at this time, the uneven structure 305 may be formed simultaneously with the engraving 302 by the above-described wet processing or the like from the production side. In the case where it is formed simultaneously with the engraving 302, the concavo-convex structure 305 is formed before the formation of the base layer 304.

At this time, the uneven structure 305 is left only in the electrode formation region, and it is necessary to smooth other regions. The smoothing can be suitably carried out, for example, by using a commercially available etching paste, by performing screen printing on the screen, etching etching, and obtaining a smoothed surface. Further, even after application of an acid-resistant photoresist or wax in the electrode formation region, the etching of the non-light-receiving surface may be performed by fluoronitric acid using a spin etching apparatus or a belt-type etching apparatus. Further, when a batch type processing apparatus is used, both the electrode formation region and the light receiving surface are applied, and the substrate is immersed in fluoronitric acid to etch the engraving. After the etching, the coating is removed using a specific chemical solution such as an alkali solution. The amount of etching of the crucible is not particularly limited. When considering the effect of reducing surface defects and productivity, it is preferably set to 0.3 to 10 μm, and more preferably 1 to 5 μm.

Further, when the non-light-receiving surface is not formed with a embossing, even before the formation of the base layer, the base layer, and the emitter layer, an uneven structure is formed in the electrode formation region of the non-light-receiving surface, and the uneven structure is obtained as shown in FIG. The structure can also be. At this time, even if it is formed by photolithography and etching, irregularities may be formed in the electrode formation region, and it is also possible to apply sandblasting to the electrode formation region. A method of forming a concavity and convexity, or a method of using a laser ablation of a crucible as disclosed in Japanese Laid-Open Patent Publication No. 2003-258285.

The formation of the base layer and the emitter layer can be directly applied to the method previously described. However, at this time, as shown in FIG. 4, the base layer 404 is formed on the non-light-receiving surface. When the concentration of phosphorus in the region other than the electrode formation region is to be suppressed, even if a method of smoothing the non-light-receiving surface of FIG. 3 is applied, the base layer 404 may be etched by screen printing or inkjet printing of the phosphorus compound. The method may be applied only to the region where the uneven structure 405 is formed and may be subjected to heat treatment.

The width or diameter of the bottom of the convex portion of the concavo-convex structure must be smaller than the line width of the electrode in order to obtain good electrical contact and adhesion between the electrode and the crucible. Since the electrode line width is generally 30 μm to 300 μm, it is preferable that the width of the uneven structure is set to an upper limit of 1/10.

As described above, in the sinterable conductive paste, the low-melting glass is dissolved, and during the precipitation and solidification, the bonding of the glass and the crucible is obtained, and by having the unevenness, the glass is precipitated to the concave portion, the convex portion Helps expand the contact area of metals. In this case, the height difference of the uneven structure is generally set to 0.5 μm or more, and more preferably 1 μm or more. In the fine unevenness of 0.5 μm or less, since the convex portion is covered with the glass, the contact resistance of the electrode is increased. In addition, the upper limit of the height difference is different depending on the thickness of the electrode, the production method, and the like. For example, when a general solar cell using screen printing is used, it is preferably 20 μm or less, and more preferably 15 μm or less. For a height difference of 20 μm or more, the conductive paste is insufficiently filled in the concave portion, and further, due to the shape of the convex portion, when the electrode is sintered, the glass is precipitated. The recess is insufficient, and most of the surface of the crucible is covered with glass to make the contact resistance large.

The width W _t of the electrode formation region formed by the above-mentioned engineering is also different depending on the design of the solar cell, but in general, it is preferably 0.8 to 1.5 times the width W _m of the electrode 308, and 1.0 to 1.3 times. good. When it is less than 0.8 times, since the electrode is applied to the smooth portion, the electrical contact with the substrate is insufficient, and when it is more than 1.5 times, the surface recombination loss of the carrier is revealed.

Further, the formation of the emitter layer may be performed even after the formation of the base layer. At this time, the smoothing process of the base layer may be performed even after the formation of the base layer, and may be performed after both the base layer and the emitter layer are formed.

Next, a tantalum nitride film or the like of about 100 nm is formed on the light-receiving surface and the non-light-receiving surface of the substrate 301 as protective films 306 and 307. Film formation using a chemical vapor deposition apparatus, using mixed metostere and ammonia as a reaction gas, nitrogen may be used instead of NH ₃ , and further, dilution of a film formation species by H ₂ gas or process pressure may be performed. Adjust, dilute the reaction gas, and achieve the desired refractive index. In order to improve the optical properties, the refractive index is preferably from 1.5 to 2.2. Further, it is not limited to the tantalum nitride film, and a single layer film such as ruthenium oxide, carbon ruthenium, amorphous tantalum, aluminum oxide, titanium oxide, tin oxide, or zinc oxide, or a combination of the laminated films may be used. can. Furthermore, even if the light-receiving surface and the non-light-receiving surface are different, a different film type can be used.

Next, the electrode 308 is screen-printed on the light-receiving surface of the substrate 301. For printing and drying Ag powder and glass powder with organic binder After the Ag paste is mixed, the Ag powder is passed through the protective film 306 by heat treatment, and the electrode and the crucible are turned on.

Further, the electrode 309 is screen-printed on the base layer of the non-light-receiving surface, and the Ag paste is mixed with the Ag powder and the glass powder and the organic binder after printing and drying for about 1 second to 5 minutes. The heat treatment is performed at 700 to 860 ° C, whereby Ag powder is passed through the protective films 306 and 307, and the electrodes and the crucible are turned on. Further, even if the electrode 307 and the electrode 308 are replaced in the order of formation, the sintering may be performed once.

The above is an example of an embodiment of a solar cell when an n-type germanium substrate is used. However, as described below, the present invention is also applicable to a solar cell using a p-type germanium substrate. The p-type germanium solar cell can be fabricated in the same manner as the above-described n-type germanium solar cell. At this time, the substrate 301 can be obtained by doping high-purity germanium with boron or aluminum, gallium or indium-like group III elements, and the resistivity can be generally adjusted. Into 0.1~5Ω. Cm.

Next, a base layer 304 is formed. It is generally suitable to use BBr ₃ to diffuse boron into the substrate by vapor phase diffusion at 900 to 1100 ° C. Furthermore, it is not limited to this, and even a boron compound which can be screen-printed or spin-coated can be used. The base layer 304 must be formed only on the non-light-receiving surface. In order to achieve this, it is necessary to perform processing such as diffusion in a state where the light-receiving surfaces of the two sheets are overlapped face-to-face, or diffusion barrier such as tantalum nitride is formed on the light-receiving surface. Barrier so that the added impurities do not diffuse to the light receiving surface.

The surface boron concentration of the base layer 304 is preferably 1×10 ¹⁹ or more and 1×10 ²¹ atoms/cm ^{3 in} order to obtain good electrical contact between the substrate and the electrode, and is set to be 5×10 ¹⁹ or more and 1×10. The degree of ²¹ atoms/cm ³ or less is more preferable. When it is less than 1 × 10 ¹⁹ atoms/cm ³ , the contact resistance between the substrate and the electrode becomes large, and the output of the solar cell decreases. 1 × 10 ²¹ atoms / cm ³ is the approximate solid solubility limit of boron. After the diffusion, the glass produced on the surface is removed with hydrofluoric acid or the like.

Next, the region other than the electrode formation region of the boron diffusion surface is smoothed. For smoothing, for example, a commercially available etching paste can be suitably used, and the uneven printing structure is etched by screen printing to obtain a smoothed surface. Further, even after application of an acid-resistant photoresist or wax in the electrode formation region, a non-light-receiving surface concavo-convex structure may be etched with fluoronitric acid using a spin etching apparatus or a belt-type etching apparatus. Further, when a batch type processing apparatus is used, both the electrode formation region and the light receiving surface are applied, and the substrate is immersed in fluoronitric acid to etch the uneven structure. After the etching, the coating is removed using a specific chemical solution such as an alkali solution.

Next, an emitter layer 303 is formed. It is generally suitable to use POCl ₃ to diffuse phosphorus into the substrate by vapor phase diffusion at 800 to 1000 ° C. Furthermore, it is not limited to this, and even a phosphorus compound which can be screen-printed or spin-coated can be used. In general, a solar cell must form a base layer 304 only on a light-receiving surface. In order to achieve this, it is necessary to perform processing such as superimposing two sheets in a state in which the non-light-receiving surfaces of the two substrates face each other to be diffused, or to be non-light-receiving. A diffusion barrier such as tantalum nitride is formed on the surface side so that phosphorus does not diffuse to the non-light-receiving surface.

The phosphorus concentration on the surface of the emitter layer 303 is preferably 1 × 10 ¹⁹ or more and 3 × 10 ²⁰ atoms/cm ^{3 , more} preferably 5 × 10 ¹⁹ or more and 1 × 10 ²⁰ atoms / cm ³ . When it is less than 1 × 10 ¹⁹ atoms/cm ³ , the contact resistance between the substrate and the electrode becomes large, and when it is set to 3 × 10 ²⁰ atoms/cm ³ or more, the defect in the emitter layer and the Auger composite The combination of the charge carriers caused by (Auger recombination) is obvious, and the output of the solar cell is lowered. After the diffusion, the glass produced on the surface is removed with hydrofluoric acid or the like. Further, the base layer may be formed even after the formation of the emitter layer. Further, the smoothing process of the base layer may be performed after forming both the base layer and the emitter layer. In the subsequent work, the same method as in the case of using the n-type germanium substrate can be applied.

Any of the above embodiments is directed to a solar cell in which a base layer is formed on a non-light-receiving surface, but the form of the solar cell is not limited thereto, and the present invention is also applicable to forming an emitter layer on a non-light-receiving surface. A solar cell in which a base layer is formed on a light-receiving surface, and is also applicable to a solar cell of a full-electrode rear surface type in which an emitter layer and a base layer are formed on a non-light-receiving surface.

[Examples] [Example 1]

150mm square, thickness 250μm and specific resistance 1Ω. The boron-doped <100> p-type raw diced ruthenium substrate is immersed in a mixed solution of 5% calcium hydroxide aqueous solution and 2-propanol at 80 ° C after removing the damaged layer by hot concentrated calcium hydroxide aqueous solution. Minutes, a random pyramid-shaped scribe is formed, followed by washing in a hydrochloric acid/hydrogen peroxide mixed solution.

Next, a diffusion surface was etched by a mixed acid solution (MH-1 manufactured by Nippon Kasei Co., Ltd.) using a rotary etching machine (MSE2000 manufactured by Sanyi Semiconductor Co., Ltd.). The discharge time of the mixed acid solution and the number of rotations of the substrate were adjusted to prepare a sample of the step etching etching.

Next, heat treatment was performed at 850 ° C for 30 minutes in a POCl ₃ atmosphere to form an emitter layer. After the diffusion, the glass layer was removed with hydrofluoric acid, washed with pure water, and dried. Further, the Ag paste was applied to the embossed surface by screen printing, and after drying, a comb-shaped electrode having an average line width of 90 μm was formed by heat treatment at 820 ° C in a conveyor belt furnace.

The uneven structure at five points on the electrode formation surface of the sample was measured by a scanning electron microscope, and the average height difference of the unevenness was calculated, and the contact resistance of the electrode was measured by a ladder method. Further, the tape test by JIS K6854 was carried out to evaluate the presence or absence of electrode peeling.

As shown in FIG. 5, when the average uneven height difference is less than about 0.5 μm, the relative value of the contact resistance sharply rises. Table 1 shows the results of the tape test. Electrode peeling occurs when the average uneven height difference is 0.3 μm or less.

[Example 2]

150mm square, thickness 250μm and specific resistance 1Ω. The boron-doped <100> p-type raw diced ruthenium substrate is immersed in a mixed solution of 5% calcium hydroxide aqueous solution and 2-propanol at 80 ° C after removing the damaged layer by hot concentrated calcium hydroxide aqueous solution. Minutes, a random pyramid-shaped scribe is formed, followed by washing in a hydrochloric acid/hydrogen peroxide mixed solution. The average uneven height difference at this time was about 2 μm.

Next, the light-receiving surfaces were superposed on each other, and heat-treated at 980 ° C for 30 minutes in a BBr ₃ atmosphere to form a base layer. Next, the non-light-receiving surfaces were superposed on each other, and heat-treated at 830 ° C for 30 minutes in a POCl ₃ atmosphere to form an emitter layer. After the diffusion, the glass layer was removed with hydrofluoric acid, washed with pure water, and dried.

Next, the etching paste (Iseshape SolarEtch(R)SiS manufactured by Merck) was screen-printed at a non-electrode-forming region of the non-light-receiving surface, and held at 170 ° C for 100 seconds, after etching to remove the engraving, Rinse with pure water.

Next, a tantalum nitride film having a film thickness of about 100 nm is formed on the light receiving surface and the non-light receiving surface by plasma CVD. Further, an Ag paste was applied to the light-receiving surface and the non-light-receiving surface by screen printing, and after drying, an electrode was formed by heat treatment at 820 ° C in a conveyor belt furnace.

[Comparative Example 1]

The substrate was formed in the same manner as in Example 1, and a substrate on which the emitter and the base layer were formed, and a tantalum nitride film having a film thickness of about 100 nm was formed on the light receiving surface and the non-light receiving surface by plasma CVD. Further, an Ag paste was applied to the light-receiving surface and the non-light-receiving surface by screen printing, and after drying, an electrode was formed by heat treatment at 820 ° C in a conveyor belt furnace.

[Comparative Example 2]

The etched substrate was formed in the same manner as in Example 1 and Comparative Example 1, and the etching paste was screen-printed on the non-light-receiving surface, and held at 170 ° C for 100 seconds. After etching and removing the embossing, the etch was washed with pure water. net.

Next, the light-receiving surfaces were superposed on each other, and heat-treated at 980 ° C for 30 minutes in a BBr ₃ atmosphere to form a base layer. Next, the non-light-receiving surfaces were superposed on each other, and heat-treated at 830 ° C for 30 minutes in a POCl ₃ atmosphere to form an emitter layer. After the diffusion, the glass layer was removed with hydrofluoric acid, washed with pure water, and dried.

Then, by plasma CVD, the light-receiving surface and the non-light-receiving surface are comprehensive. A tantalum nitride film having a film thickness of about 100 nm is formed. Further, an Ag paste was applied to the light-receiving surface and the non-light-receiving surface by screen printing, and after drying, an electrode was formed by heat treatment at 820 ° C in a conveyor belt furnace.

The current-voltage characteristics were measured under the dark state of Example 1 and Comparative Example 1 and Comparative Example 2 and the pseudo-sunlight irradiation of an atmospheric optical path of 1.5 g. As shown in Table 2, in Example 1, the open voltage and the curve factor were simultaneously improved, indicating the highest conversion efficiency.

[Industrial use feasibility]

According to the present invention, it is possible to form a high-quality PR structure easily and inexpensively on the back surface of a crystal solar cell, and it is extremely effective for increasing the efficiency and cutting costs of the solar cell.

301‧‧‧Substrate

302‧‧‧ Engraving

303‧‧ ‧ emitter layer

305‧‧‧Concave structure

306, 307‧‧ ‧ protective film

308, 309‧‧‧ electrodes

304‧‧‧ base layer

Claims (5)

A solar cell comprising: a crystallization substrate having a first conductivity type; an emitter layer having a second conductivity type formed on the crystallization substrate; and a group having a first conductivity type formed on the crystallization substrate In the electrode layer, an electrode for extracting electric charges excited by light incident on the substrate to the outside is formed in the emitter layer and the base layer, respectively, and an area in which the electrode is formed in the substrate At least a part of the structure has a concave-convex structure having a plurality of irregularities. The solar cell according to claim 1, wherein at least one of the electrodes is formed on a non-light-receiving surface of the substrate, and at least a portion of the non-light-receiving surface except the region in which the electrode is formed is smoother than the uneven structure. The solar cell according to claim 1 or 2, wherein a difference in height between the concave portion and the convex portion in the uneven structure is 0.5 μm or more. The solar cell according to any one of claims 1 to 3, wherein the electrode is a sintered body of metal particles and glass. A solar cell module, which is electrically connected to the solar cell described in any one of claims 1 to 4.