JP2005260149A - Method of manufacturing photovoltaic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photovoltaic device in which deterioration of an amorphous semiconductor layer is eliminated and sneak of the film which causes the current leakage is eliminated to enhance the cell characteristics. <P>SOLUTION: The photovoltaic device comprises a laminate consisting of an i-type amorphous silicon film 2, a p-type amorphous silicon film 3, and an ITO film 4, on a surface of an n-type single-crystal silicon substrate 1, and an i-type amorphous silicon film 6, an n-type amorphous silicon film 7, and an ITO film 8 on the rear surface of the substrate 1. The method of manufacturing the photovoltaic device is to form a groove 11 on the side surface of the substrate 1, whose width and depth are larger than the total film thickness of the laminate consisting of the i-type amorphous silicon film 2, the p-type amorphous silicon film 3, and the ITO film 4 formed on the substrate, and to subsequently form the laminate consisting of the i-type amorphous silicon film 2, the p-type amorphous silicon film 3 and the ITO film 4, and on the rear surface of the substrate 1, the i-type amorphous silicon film 6, the n-type amorphous silicon film 7, and the ITO film 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a photovoltaic device using a semiconductor junction.

  In recent years, research and practical application of solar cells using crystalline silicon such as single crystal silicon and polycrystalline silicon as photovoltaic elements have been actively conducted. In particular, a solar cell having a heterojunction formed by combining amorphous silicon and crystalline silicon can form the junction by a low-temperature process of 200 ° C. or less, and obtain high conversion efficiency. It attracts attention because it is. In such a photovoltaic device, in order to improve the photoelectric conversion efficiency, it is necessary to improve the fill factor (FF) while maintaining a high short circuit current (Isc) and an open circuit voltage (Voc).

  Therefore, a sun having a so-called HIT structure in which a substantially intrinsic amorphous silicon film (i-type amorphous silicon film) is inserted between an n-type single crystal silicon substrate and a p-type amorphous silicon film. A battery has been developed (see, for example, Patent Document 1).

  On the other hand, in the production of a photovoltaic device combining a conventional amorphous semiconductor and crystalline silicon, unlike a photovoltaic device made only of crystalline silicon, non-forming for forming a junction on a crystalline silicon substrate is performed. It is necessary to form a crystalline silicon layer or a conductive thin film.

  Here, conventionally, when these films are formed on a substrate, an amorphous silicon layer or a conductive thin film is formed only on the surface of the substrate in order to use a manufacturing method such as plasma CVD, sputtering, or vapor deposition. In other words, it wraps around the side surface or the back surface, causing a short circuit of the element through these, resulting in a problem of a decrease in output due to leakage.

In order to solve the above-described problems, an amorphous semiconductor layer and a conductive thin film that form a heterojunction with the substrate are formed on the entire front and back surfaces of a one-conductivity-type crystalline semiconductor substrate, and then non-exposed by a laser. A method for suppressing a leakage current path by removing a crystalline semiconductor layer and a conductive thin film has been proposed (see, for example, Patent Document 2).
JP-A-11-224954 JP-A-9-129904

  According to the method according to Patent Document 2 described above, the amorphous semiconductor layer and the conductive thin film are removed by a laser, so that a short circuit of the photovoltaic element due to wraparound is effectively prevented. However, when laser processing is performed after forming an amorphous semiconductor layer and a conductive thin film, the amorphous semiconductor layer at the laser-processed end is altered, microcrystallized, and altered microcrystal-like. There is a problem that a leak current occurs in the semiconductor layer and cell characteristics deteriorate.

  The present invention has been made in view of the above-described conventional problems, and eliminates the deterioration of the amorphous semiconductor layer, eliminates the wraparound of the film, and eliminates leakage current to improve cell characteristics. The purpose is to provide.

  The present invention comprises a laminate composed of an amorphous semiconductor layer of another conductivity type and a conductive thin film on the surface of a crystalline semiconductor substrate of one conductivity type, and at least a back electrode film is provided on the back surface of the substrate. A method of manufacturing a photovoltaic device according to claim 1, wherein a groove having a width and a depth larger than the larger sum of the film thicknesses of the films provided on the front and back surfaces of the substrate is formed on the side surface of the substrate. Thereafter, at least a back electrode film is provided on the back surface of the substrate, which is a laminated body including an amorphous semiconductor layer of another conductivity type and a conductive thin film.

  The substrate is formed of a single crystal silicon substrate, and irregularities are formed by anisotropic etching, and a groove having a width not exceeding 100 μm and a depth not less than 10 μm and not more than 120 μm is preferably formed on the side surface by laser processing.

  As described above, according to the present invention, by forming a groove on the side surface of the substrate in advance, it is possible to generate a large leakage current path so that the conductive films on the front and back sides are reliably separated on the side surface of the substrate and are electrically connected. It can suppress and a solar cell characteristic improves.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a photovoltaic device according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part of the photovoltaic device according to the embodiment of the present invention.

  An n-type single crystal silicon wafer having a resistivity of about 1 Ω · cm and a thickness of about 300 μm and having a (100) plane is prepared. An uneven pyramid structure of about 10 μm is formed by anisotropic etching using (NaOH). The thickness of the silicon wafer on which the irregularities are formed is 240 μm.

  On the side surface of the n-type single crystal silicon substrate 1 provided with the pyramidal irregularities, a groove 11 having a desired width and depth is formed around the side surface using a YAG laser. This width and depth form a rectangular groove 11 having a larger width and deeper depth than the larger one of the total thicknesses formed on the front and back surfaces in a subsequent process. This is to prevent the film formed in the groove 11 from wrapping around to prevent the film formed on the front and back sides from being connected to prevent the film formed later.

  In this embodiment, as will be described later, since the amorphous silicon film is about 10 nm and the transparent conductive film is about 100 nm, the groove 11 having a width and depth exceeding 120 nm may be formed. In the case of processing using a laser, the width exceeds 20 μm, so the above conditions are satisfied. Further, since the depth of about 2 μm is processed, the above condition is satisfied. If the width and depth of the groove 11 are too large, there is a problem of strength. In the case of the substrate 1 having a thickness of 240 μm, the width should not exceed 100 μm and the depth should not exceed 120 μm.

  The substrate 1 in which the grooves 11 are formed is cleaned according to a normal method to remove impurities, and a thickness of about 10 nm is formed on the upper surface of the n-type single crystal silicon substrate 1 using a known RF plasma CVD (13.56 MHz). On the substantially intrinsic i-type amorphous silicon film 2 and the i-type amorphous silicon (a-Si) film 2 having p-type amorphous silicon (a-Si) having a thickness of about 10 nm A film 3 is formed. The conditions for forming this film are shown in Table 1.

An ITO film 4 is formed on the p-type amorphous silicon (a-Si) film 3 by sputtering as a transparent conductive film having a thickness of about 100 nm. The ITO film 4 is made of In ₂ O ₃ to which SnO ₂ is added.

The ITO film 4 is formed by sputtering as follows. The SnO ₂ powder is 5 wt%, and a sintered body with In ₂ O ₃ powder is used as a target, which is placed on the cathode. In addition, at least one of Si, Ge, and Ti may be used as a dopant. An appropriate amount of these compound powders may be mixed with indium oxide powder and sintered to prepare a target. It is possible to change the amount of Sn in the ITO film by changing the amount of SnO _2. However, in order to improve the light transmittance of ITO, the amount of Sn with respect to In is 1 to 10 at%. Furthermore, 2 to 7 at% is preferable. The sintered density of the target is preferably 90% or more.

In order to suppress plasma damage during film formation, use a device that can apply a strong magnetic field of 300 to 3000 Gauss from the magnet to the cathode surface, place the element facing the cathode in parallel, and then evacuate the chamber To do. The substrate temperature is heated from room temperature to 200 ° C. with a heater. Further, a mixed gas of Ar and O ₂ is flowed to maintain the pressure at 0.4 to 1.3 Pa, and DC power is applied to the cathode at 0.5 to 2 kW to start discharging. The film formation rate was about 10 to 80 nm / min with the substrate stationary with respect to the cathode.

  By forming the ITO film 4 with a thickness of 100 nm under such conditions, the ITO film 4 is reliably separated by the grooves 11.

  Further, a comb-shaped collector electrode (paste electrode) 5 is formed in a predetermined region on the upper surface of the ITO film 4. The comb-shaped electrode 5 is composed of a conductive filler made of silver (Ag) and a thermosetting resin, and is formed in a predetermined pattern made up of finger portions and bus bar portions by printing.

  Further, a substantially intrinsic i-type amorphous silicon (a-Si) having a thickness of about 10 nm is formed on the lower surface of the n-type single crystal silicon substrate 1 using a known RF plasma CVD (13.56 MHz). An n-type amorphous silicon (a-Si) film 7 having a thickness of 10 nm is formed on the film 6 and the i-type amorphous silicon (a-Si) film 6. As described above, the i-type amorphous silicon (a-Si) film 6 and the n-type amorphous silicon (a-Si) film 7 are sequentially formed on the lower surface of the n-type single crystal silicon substrate 1. A so-called BSF (Back Surface Field) structure is formed.

  On the n-type amorphous silicon (a-Si) film 7, an ITO film 8 having a thickness of 100 nm is formed by the same formation method as that for the surface side. A comb-shaped collector electrode (paste electrode) 9 is formed in a predetermined region on the ITO film 8.

  Table 1 shows the formation conditions of amorphous silicon (a-Si) at the time of producing a typical solar cell by the RF plasma CVD method.

  Table 2 shows a conventional structure in which a non-deposition region of an a-Si film and an ITO film is formed on the end face using a mask, and an entire surface on which the a-Si film and the ITO film are formed up to the end face of the substrate without using a mask for expanding the effective area. Solar cells each having a groove having a width of 40 μm and a depth of 40 μm were formed in the central portion of the side surface of the formation structure and the substrate 1 according to an embodiment of the present invention, and the characteristics were compared. The film forming conditions and the like were all made the same by the method described above.

  As can be seen from Table 2, although the current increases in the entire surface formation structure as the effective area is increased compared to the conventional structure, the a-Si film at the end face, the leakage current path due to the wraparound of the ITO film, particularly the a-Si film The leakage current due to the ITO film having a lower electrical resistance than F. However, the output was rather lowered. On the other hand, according to the embodiment of the present invention, the ITO film is completely separated by the groove 11 on the end face, and the occurrence of a leakage current path is suppressed. F. And high current.

Table 3 shows the normalized F.D. when the width of the groove 11 is constant at 40 μm and the depth is changed to 2 to 120 μm at the center of the side surface (thickness 240 μm) of the substrate 1. F. Is a change. Normalization was performed according to the values for the entire surface formation in Table 1.

  From Table 3, the standardized F.D. Although F is improved, the improvement effect is small up to 5 μm. This is because the substrate is provided with irregularities on the substrate surface by alkali etching, and the same irregularities as the substrate surface having a size of about 10 μm are formed on the side surface of the substrate. For this reason, it is considered that the formation of the groove shallower than the concavo-convex is because the controllability is not sufficient and the effect of the present invention cannot be sufficiently obtained. However, when the depth is deeper than 10 μm, the effect becomes clear and it is considered that the leakage path was successfully separated through the ITO film intended in the present invention.

  Next, the standardized F.D. when the depth of the groove 11 is fixed at 10 μm and the width is changed at 20 to 100 μm. F. Is shown in Table 4. Normalization was performed according to the values for the entire surface formation in Table 1. From Table 4, the same level of effect was obtained in any case.

  Subsequently, after the formation of the transparent conductive film, the amorphous silicon film / transparent conductive film is removed by laser to compare the solar battery cell formed by the method for suppressing the leakage current path with the solar battery cell according to the present invention. Table 5 shows the results of the test.

  As a result, when post-processing was performed with a laser, the damage of the crystalline silicon on the substrate end face became clear from the transmission electron micrograph, and the alteration (microcrystallization) of the silicon at the laser-processed end was also confirmed. As a result, recombination centers increase at the silicon substrate end face, and leakage current is generated in the modified microcrystalline-like silicon. F. Etc. are thought to have declined. On the other hand, in the present invention in which the substrate 1 is processed in advance as compared with post-processing, it is possible to remove the damaged layer by the cleaning process, and there is no possibility of alteration of the a-Si film or the transparent conductive film, which is effective. I understand that there is.

  In the embodiment described above, the groove 11 is provided on the substrate 1 by YAG laser processing. However, the groove 11 may be formed by photolithography and etching.

1 is a sectional view of a photovoltaic device according to an embodiment of the present invention. It is a principal part expanded sectional view of the photovoltaic apparatus by embodiment of this invention.

Explanation of symbols

1 n-type single crystal silicon substrate 2 i-type amorphous silicon layer 3 p-type amorphous silicon layer 4 ITO film 5 comb-shaped collector electrode 6 i-type amorphous silicon layer 7 n-type amorphous silicon layer 8 ITO film 9 Comb collector 11 Groove

Claims (3)

A photovoltaic device comprising a laminate comprising an amorphous semiconductor layer of another conductivity type and a conductive thin film on the surface of a crystalline semiconductor substrate of one conductivity type, and at least a back electrode film provided on the back surface of the substrate. A method for manufacturing a power device, wherein a groove having a width and depth larger than the larger sum of the film thicknesses of the films provided on the front and back surfaces of the substrate is formed on the side surface of the substrate, Thereafter, a laminate comprising an amorphous semiconductor layer of another conductivity type and a conductive thin film, and at least a back electrode film is provided on the back surface of the substrate. The substrate is made of a single crystal silicon substrate, and irregularities are formed by anisotropic etching, and a groove having a width not exceeding 100 μm and a depth not less than 10 μm and not more than 120 μm is formed on the side surface by laser processing. A method for manufacturing a photovoltaic device, which is characterized. 3. The semiconductor device according to claim 1, wherein single crystal silicon is used as the one conductivity type crystalline semiconductor substrate, and a semiconductor layer made of an amorphous or microcrystalline silicon semiconductor is provided at least on a light incident side. Photovoltaic device manufacturing method.

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