TWI503999B - Solar cell and manufacturing method thereof - Google Patents

Description

Solar battery unit and method of manufacturing same

The present invention relates to a solar cell unit and a method of manufacturing the same.

At present, as a surface reflection preventing structure of a solar battery cell, a texture structure formed by wet etching through an alkaline solution or an oxygen solution is generally used. On the other hand, it is known that a structure (so-called sub-wavelength structure) in which irregularities of the same or finer wavelength as the wavelength of sunlight are periodically formed is used for the surface reflection preventing structure, and a lower reflectance is achieved. Therefore, the user who uses the sub-wavelength structure as the surface reflection preventing structure of the solar battery cell can be expected to lower the reflectance than in the related art and increase the output current. For example, in the case of the sub-wavelength structure, the user can use the nano-column array structure, which will be described later, as the surface reflection preventing structure, and the user can compare the solar cell with the conventional structure. The increase in output current is displayed by simulation.

The structure of the nanocolumn solar cell units described and studied later has been classified into three types. These 3 types are indicated Nanowire Solar Cell (subsurface-junction), Nanowire Solar Cell (planar-junction), and Nanowire Solar Cell (radial-junction) shown in Table 2 of Non-Patent Document 1. The Nanowire system here is synonymous with the nano column of this specification. Hereinafter, in the present specification, a Nanowire Solar Cell (subsurface-junction) is described as a planar deep junction type nano column solar battery cell, and a Nanowire Solar Cell (planar-junction) is described as a planar shallow junction type nano column solar energy. In the battery unit, the Nanowire Solar Cell (radial-junction) is described as a radial junction type nano column solar battery unit.

Here, in the above-described three types of solar battery cells, a pn junction is formed by forming an n+ layer in which a high concentration of impurities is doped on the surface of the p-type substrate (p and n may be reversed). Hereinafter, a "layer in which a high concentration is doped with an impurity" is described as an "emitter layer". The role of the emitter layer is mainly to form the potential difference of the pn junction and separate the electrons from the hole, function as a conduction path for the carrier collected in the emitter layer to reach the electrode, and reduce the contact impedance with the electrode. The role of 3 points. In the planar deep junction type nano column solar cell and the planar shallow junction type nano column solar cell, the pn junction surface is formed in a planar shape parallel to the substrate surface. On the other hand, in the radial junction type nano column solar cell, the pn junction surface is formed in parallel with the surface of the nano column.

Here, the difference between the above three types of solar cells is located at the position of the emitter layer in the nano column. Deep joint type nai in planar In the rice column solar cell unit, the emitter layer exists in the entire range of the nano column. In this regard, in the planar shallow junction type nano column solar cell, the emitter layer is present on the top of the column. Further, in the radial junction type nano column solar cell, the emitter layer is present in the side wall portion of the column. As described above, although the positions of the emitter layers in the nano-pillar are different, in the conventional nano-pillar solar cell structure, the point system of the emitter layer exists in at least a part of the column of the nano column. For common.

Further, Non-Patent Document 2 discloses that the carrier generation rate distribution in the nano-column solar cell is investigated by simulation, and the carrier generation rate inside the nano-column is shown to be directly below The carrier yield of the substrate is higher by two to three digits.

However, Patent Document 1 discloses a solar cell in which a plurality of openings having light effect on the surface of the substrate are provided. In view of the structure related to the third embodiment of the present invention, the opening width of the opening portion is approximately 1 to 15 μm, which is different from the sub-wavelength structure. . Accordingly, the technique described in Patent Document 1 is expected to have a configuration different from that of Embodiment 3 of the present invention. The details are described later in the third embodiment.

[Previous Technical Literature] [Patent Document]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2011-77370

[Non-patent literature]

Non-Patent Document 1: IEEE IEDM Technical Digest, pp. 856 - 859 (2011).

Non-Patent Document 2: IEEE IEDM Technical Digest, pp. 704 - 707 (2010).

<For recombination loss>

As described above, the emitter layer has a useful function for the solar cell, and the case of providing the emitter layer itself is necessary. However, in the conventional three types of solar battery cells, there is an emitter layer in the nano column, and there is a problem that the recombination loss is large. Hereinafter, a nano column solar battery cell will be taken as an example, and this problem will be described.

9 is a result of a review conducted by the inventors before the present invention, and a nanocolumn array structure in which a nanocolumn 2 having a diameter of 40 nm and a height of 200 nm is arranged on the substrate 1 at intervals of 40 nm is subjected to an FDTD method ( The result of the carrier generation rate distribution when light having an incident wavelength of 460 nm is calculated by Finite Differential Time Domain method). In Fig. 9, the darker the range of black, the higher the carrier generation rate, and conversely, the white range is that the carrier generation rate is low. Similarly to the result of Non-Patent Document 2, in FIG. 9, the carrier generation rate in the inside of the column 2 is higher than that in the substrate. Moreover, it is also understood from Fig. 9 that in the inside of the nanocolumn 2, the carrier generation rate in the side wall portion is particularly high.

Here, in a semiconductor doped with a high concentration, it is understood that the probability of recombination of the Auger becomes high in various recombination processes. In addition, the life of the Auger recombination is also shortened as the concentration of impurities increases. Therefore, the semiconductor which is doped at a high concentration causes light absorption, and the electron hole pair is generated. These carriers are in a short period of time, and the probability of elimination by the Auger recombination is also high. Along with the fact that there is a solar cell having an emitter layer in the nanocolumn, the loss due to the recombination of the Auger is a problem.

In the conventional three-column solar cell structure, in the planar deep junction type nano column solar cell, the volume occupied by the emitter layer is larger than that of the other two types, and the recombination loss is the largest. . For comparison, in the planar shallow junction type nano column solar cell unit and the radial junction type nano column solar cell unit, the emitter layer is thinned, and the recombination loss is relatively small, but These systems are also incapable of avoiding the recombination loss of the emitter layer doped with a high concentration in the range of at least a portion of the nanopillar. Further, as described above, as shown in Fig. 9, the carrier generation rate in the side wall portion of the nanocolumn 2 is particularly high as the carrier generation rate distribution in the inside of the nanocolumn 2. In this case, in the radial junction type nano column solar battery cell, although the emitter layer is formed into a thin film, when all the side wall portions are doped with a high concentration, there is a fear that the recombination loss becomes large.

<For surface electrode>

As another problem of the conventional solar battery unit, The subject of the surface electrode is described. In the planar deep junction type nano column solar cell, the emitter layer is formed as a continuous layer, and even if the surface electrode is provided in any of the emitter layers, the entire emitter layer can be made. The carrier reaches the surface electrode. Therefore, the surface electrode can be placed in a different range from the nano column. Subsequently, the surface electrode is generally used in a crystalline Si solar cell, but may also be a finger made of a non-transparent metal of Ag or Al. The electrode of the bus bar pattern may be used in a thin film solar cell, and a transparent conductive oxide such as ITO (In-Sn-O) may be formed on the entire electrode.

On the other hand, in the planar shallow junction type nano column solar cell and the radial junction type nano column solar cell, as the surface electrode, the finger shape cannot be used. The electrodes of the bus bar pattern must be formed using a full-surface electrode, and as a result, the electrode material is limited to a transparent conductive oxide such as ITO. The reason is as follows. First, in the case of a planar shallow junction type nano column solar battery cell, an emitter layer is formed only on the top of the nano column, and the emitter layers in different nano columns are isolated from each other. Accordingly, in order to collect the carrier from the emitter layers, it is necessary to electrically connect the electrodes to the isolated plurality of emitter layers, and it is necessary to form the electrodes in a comprehensive manner without using the pattern electrodes. Further, in the case of the radial junction type nano column solar battery cell, as described above, the sheet resistance of the emitter layer is increased in order to thin the emitter layer, and as a result, when the pattern electrode is used, the series impedance loss becomes For the sake of the big reason, it is necessary to use a full-surface electrode as a surface electrode system.

Such as the above two units, for the necessary formation of electrodes in a comprehensive In the case of the unit structure, the upper portion of the nano column is also covered by the electrode, and the metal such as Ag or Al which reflects sunlight is not used as the surface electrode. Thus, the material of the surface electrode is defined as a transparent conductive oxide.

When a transparent conductive oxide such as ITO is used as the surface electrode, contact resistance between the emitter layer and the transparent conductive oxide and loss due to light absorption of the transparent conductive oxide occur.

First, the contact impedance is described. When compared with the metal of Ag or Al which is generally used as the material of the pattern electrode, the transparent conductive oxide of ITO or the like has a high contact resistance with a semiconductor material such as Si. In general, the contact resistance can be lowered by increasing the surface impurity concentration of the semiconductor. However, as described above, in the solar cell unit, the increase in the surface impurity concentration causes an increase in the recombination loss, and cannot be contacted. Those whose impedance is lowered to arbitrarily increase the surface impurity concentration. Accordingly, when the transparent conductive oxide is used as the surface electrode, it is difficult to avoid both the loss through the high contact resistance and the recombination loss.

Further, in general, a transparent conductive oxide is known to absorb ultraviolet light or infrared light, and when it is used as a surface electrode, a loss of light amount reaching the light absorbing layer of the solar battery cell is reduced. In the above case, when a transparent conductive oxide such as ITO is used as the surface electrode, the characteristics of the solar cell are degraded.

When merging above, the subwavelength structure, especially the nanometer The column array structure is used as a surface reflection preventing structure, and the problems of the conventional solar cell are as follows. First, in a solar battery cell in which an emitter layer doped at a high concentration in a nano column is present, there is a problem that the recombination loss is large. Secondly, in the case where the emitter layers are used as isolated solar cells or the emitter layer is used as a thinned solar cell, as the surface electrode, the pattern electrode cannot be used, and it is necessary to use a transparent conductive oxide which forms ITO or the like. As a result of the overall electrode, there is a loss due to the contact resistance between the emitter layer and the transparent conductive oxide and the light absorption by the transparent conductive oxide. In the solar battery cell having the sub-wavelength structure, the method for solving the above two problems has not been conventionally used.

The present invention has been made in view of the above circumstances, and an object thereof is to realize a solar cell unit in which a re-bonding loss in a sub-wavelength structure can be reduced and a pattern electrode is used as a surface electrode. The above and other objects and novel features of the present invention will become apparent from the description and appended claims.

The configuration represented by the invention disclosed in the present application will be briefly described as follows.

First, a solar battery cell comprising: a plurality of pillars extending in a specific direction; and a substrate of a first conductivity type and a substrate bonded to the substrate, different from the second conductivity of the first conductivity type Type of emitter layer, plural column system by first conductivity type semiconductor In this case, each of the plurality of column systems is joined to the aforementioned emitter layer in its side.

According to a second aspect of the invention, there is provided a solar battery cell comprising: a first conductive type substrate having a plurality of columnar recesses on a surface thereof; and a portion provided on a surface of the substrate and not provided with a columnar recess, and the first The second conductivity type emitter layer having different conductivity types has a columnar recess having a width of 1 μm or less.

According to a third aspect of the invention, in a method of manufacturing a solar cell, the first pattern of the second conductivity type emitter layer different from the first conductivity type is formed on the surface of the first conductivity type substrate by using a metal pattern as a mask. Engineering, and a second engineer who uses a metal pattern to form a plurality of columns of the first conductivity type on the surface of the substrate.

According to the present invention, in the solar battery cell having the sub-wavelength structure, the recombination loss inside the sub-wavelength structure can be reduced, and the pattern electrode can be used as the surface electrode.

1‧‧‧Substrate

2‧‧‧Neizhu

3‧‧‧ convex

4‧‧‧Nemicon

11‧‧ ‧ emitter layer

12‧‧‧ Passivation film

13‧‧‧ surface electrode

21‧‧‧BSF layer

22‧‧‧Back electrode

31‧‧‧ photoresist

32‧‧‧catalyst metal

33‧‧‧ etching mask

Fig. 1(a) is a top view of a nanocolumn solar cell unit according to Embodiment 1 of the present invention.

Fig. 1(b) is a cross-sectional view showing a nanocolumn solar cell unit according to Embodiment 1 of the present invention.

Figure 2 (a) is only from the nano column of the embodiment 1 of the present invention. The top view of the passive cell structure is removed from the solar cell.

Fig. 2 (b) is a cross-sectional view showing only the structure of the passivation film removed from the column solar cell of Example 1 of the present invention.

Fig. 3 (a) is a first top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (b) is a first cross-sectional view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (c) is a second top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (d) is a second cross-sectional view showing a first manufacturing method of the nanocolumn solar battery cell according to the first embodiment of the present invention.

Fig. 3 (e) is a third top view showing a first manufacturing method of the column solar cell of the first embodiment of the present invention.

Fig. 3 (f) is a third cross-sectional view showing a first manufacturing method of the nanocolumn solar battery cell according to the first embodiment of the present invention.

Fig. 3 (g) is a fourth top view showing a first manufacturing method of the nanocolumn solar battery cell according to the first embodiment of the present invention.

Fig. 3 (h) is a fourth cross-sectional view showing a first method of manufacturing the nanocolumn solar cell of the first embodiment of the present invention.

Fig. 3 (i) is a fifth top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (j) is a fifth sectional view showing a first manufacturing method of the nanocolumn solar battery cell according to the first embodiment of the present invention.

Figure 3 (k) shows the nanocolumn of the embodiment 1 of the present invention. The sixth top view of the first manufacturing method of the solar battery unit.

Fig. 3 (l) is a sixth sectional view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (m) is a seventh top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (n) is a seventh sectional view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (o) is an eighth top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 3 (p) is a cross-sectional view showing the eighth manufacturing method of the first column solar cell of the first embodiment of the present invention.

Fig. 4 (a) is a first top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 4 (b) is a first cross-sectional view showing a first method of manufacturing the nanocolumn solar cell of the first embodiment of the present invention.

Fig. 4 (c) is a second top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 4 (d) is a second cross-sectional view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 4 (e) is a third top view showing a first manufacturing method of the nanocolumn solar battery cell of the first embodiment of the present invention.

Fig. 4 (f) is a third cross-sectional view showing a first method of manufacturing the nanocolumn solar cell of the first embodiment of the present invention.

Figure 5 (a) is a nano-groove sun relating to Embodiment 2 of the present invention. The above figure of the battery unit.

Figure 5 (b) is a cross-sectional view showing a nanochannel solar cell of Embodiment 2 of the present invention.

Fig. 6(a) is a top view showing only the structure of the passivation film removed from the nanochannel solar cell of Example 2 of the present invention.

Fig. 6 (b) is a cross-sectional view showing only the structure of the passivation film removed from the nanochannel solar cell of Example 2 of the present invention.

Fig. 7 (a) is a top view of a nanoporous solar cell unit according to Example 3 of the present invention.

Fig. 7 (b) is a cross-sectional view showing a nanopore solar battery cell of Example 3 of the present invention.

Fig. 8(a) is a top view showing only the structure of the passivation film removed from the nanopore solar cell unit of Example 3 of the present invention.

Fig. 8 (b) is a cross-sectional view showing only the structure of the passivation film removed from the nanoporous solar cell unit of Example 3 of the present invention.

9 is a result of a carrier generation rate distribution when light having an incident wavelength of 460 nm is calculated by an FDTD method for a nanocolumn array structure in which a nanometer column having a diameter of 40 nm and a height of 200 nm is arranged at intervals of 40 nm.

Example 1 <Definition of terms>

In this specification, in the sub-wavelength structure, the nano column is also adopted. Array structure, nanopore array structure, and three types of structures of nano-groove array structure. Hereinafter, the definitions of the three types of structures will be described. The nano-column array structure is a columnar structure (hereinafter referred to as "nano column" or "column") which is equivalent to the wavelength of sunlight or has a finer width, and is periodically arranged on the surface of the substrate. Construction. The column axis direction of the columnar structure is perpendicular to the substrate surface. In the following examples, a column is exemplified as the column of the nano column, but a different cross-sectional shape such as a corner column may be used. The nanopore array structure refers to a structure in which a columnar structure having a finer width is formed in the same manner as the wavelength of sunlight, and the structure is periodically opened on the surface of the substrate. The column axis direction of the columnar structure is perpendicular to the substrate surface. Similarly, the shape of the columnar structure is not a cylinder, but may be a different sectional shape such as a corner post. The nano-groove array structure means that the convex portions having the same wavelength as the sunlight or having a finer width are periodically arranged on the surface of the substrate, and as a result, there are periodic grooves (grooves) between the convex portions. Construction. The cross-sectional shape of the convex portion is generally a quadrangle, a triangle, or a fan shape. When viewed from the upper surface of the substrate, the nano-pillar array structure and the nanopore array structure have a one-dimensional periodic structure for a structure having a periodicity of two dimensions. However, the columnar structure and the "width" of the convex portion are taken as the length parallel to the direction of the substrate surface.

When the reflection preventing effect of these three types of sub-wavelength structures is described, the reflectance of the nano-pillar array structure and the nanopore array structure is generally the same, and the nano-groove array structure is the same as the above 2 When the types of structures are compared, the reflectance is generally high. In addition, the nano-column array structure and the nanopore array structure are not from the incident light. The vertical direction enters the substrate surface from the oblique direction, and also shows a relatively low reflectance. However, the nano-groove array structure is known to reflect the reflectance when the light enters the vertical direction to the groove. The taller. As described above, the three types of sub-wavelength structures are different in point of the anti-reflection effect, but they are all objects of the present invention as described below. In the present specification, a nano-column array structure, a nanopore array structure, and a nano-groove array structure are provided as solar cell units having a surface reflection preventing structure, and each is described as a nano column solar cell unit, and a nanopore solar cell Battery unit, nano-groove solar cell unit.

However, in the following embodiments, the substrate or the like is referred to as a p-type, and the emitter layer is described as an n-type. However, the same configuration may be considered as the opposite configuration, and the present application is hereby incorporated by reference. The scope of the technical scope of the invention.

<unit construction>

1(a) and 1(b) are a top view and a cross-sectional view of a nanocolumn solar cell unit according to Embodiment 1 of the present invention. The nanocolumn solar cell of Example 1 was attached to a substrate 1, and a nanocolumn solar cell of a nanocolumn 2 was formed. Fig. 1 shows a structure in which the column 2 is cylindrical. However, as described above, the column 2 can also be a column or the like having a columnar structure having different cross-sectional shapes. The passivation film 12 is formed on the outermost surface of the nanopillar 2 and the emitter layer 11, but the passivation film 12 is not present directly under the surface electrode 13, and the emitter layer 11 and the surface electrode 13 are in contact with each other. Figure 1 (b) is a cross-sectional view of whether there are isolated or not The emitter layer 11 is actually, but the emitter layer 11 is spread over a layer that is continuous over the substrate 1. To show this, the top view and the cross-sectional view of the structure in which only the passivation layer 12 is removed from the nanocolumn solar cell structure of the first embodiment are shown in Figs. 2(a) and 2(b). As shown in the upper diagram of Fig. 2(a), the range of the emitter layer 11 between the nano-columns 2 is, without being isolated from each other, continuous throughout the substrate 1.

In general, a solar cell is configured by semiconductor pn bonding or pin bonding, or Schottky bonding of a semiconductor and a metal. Hereinafter, a solar battery cell configured by pn bonding will be described. In the nanocolumn solar cell of the first embodiment, the substrate 1 and the nanopillar 2 are made of a conductive (first conductivity type) semiconductor material. Hereinafter, the case where the substrate 1 and the nano-pillar 2 are both p-type semiconductors will be described, but the present invention is also applicable to the case where the p-type and the n-type are opposite. When the substrate 1 and the nano-pillar 2 are p-layers, the emitter layer 11 is doped at a high concentration, and a conductive type (second conductivity type) layer different from the first conductivity type is used, and the substrate 1 and the substrate are provided. When the rice column 2 is a p-type, it is an n ⁺ layer. Accordingly, the substrate 1 and the nano-pillar 2 and the emitter layer 11 form a pn junction. In particular, the nanopillar 2 is formed with a pn junction with the emitter layer 11 on its side surface, and does not form a pn junction with the emitter layer 11 at its front end portion. Further, in the solar battery cell, the same conductivity type as the substrate is used, and a BSF (Back Surface Field) layer doped with a high concentration is generally formed between the substrate and the back surface electrode. In the nanocolumn solar cell of the first embodiment, a BSF layer 21 made of a p ⁺ layer is formed between the substrate 1 and the back surface electrode 22. However, in FIG. 1, a structure in which the BSF layer 21 and the back surface electrode 22 are spread over the entire surface is shown, but for example, a passivation film is formed between the BSF layer 21 and the back surface electrode 22, and is removed only in a partial range. The passivation film is in contact with the BSF layer 21 and the back surface electrode 22, and a so-called point contact structure may be used.

The material constituting the nanocolumn solar cell of Example 1 will be described. The substrate 1 of the light absorbing layer, the material of the nano-pillar 2, the emitter layer 11, and the BSF layer 21 are semiconductors of Si, CdTe, CuInGaSe, InP, GaAs, Ge, etc., which may adopt single crystal, polycrystalline, Various structures such as microcrystals, amorphous, and the like. The material of the passivation film 12 is an insulator such as SiO ₂ , SiN (tantalum nitride), amorphous Si, SiC (cerium carbide), CdS, or the like, or a laminated structure of these insulators. The material of the surface electrode 13 and the back surface electrode 22 is a metal such as Ag, Al, Ti, Pd, Ni, Cu, or the like, or a laminated structure thereof.

As described above, the solar battery cell of the first embodiment is characterized in that the substrate 1 having the plurality of columns 2 extending in a specific direction and being the first conductivity type (p type) is bonded to the substrate 1 and provided. Unlike the second conductivity type (n-type) emitter layer 11 of the first conductivity type, the plurality of pillars 2 are formed of a first conductivity type semiconductor, and the plurality of pillars 2 are formed on the side surface thereof and the emitter. Layer 11 joiner. Here, the impurity concentration of the emitter layer 11 is higher than the impurity concentration of the plurality of columns 2.

The solar cell system according to Example 1 has the following effects via the related configuration. First, the emitter layer 11 can be used as a structure that is not provided inside the nano-pillar 2. Thereby, the advantage of passing through the emitter layer 11 can be enjoyed at the same time, and the recombination loss inside the nanocolumn can be reduced. Probability.

Second, the emitter layer 11 can be used as a continuous layer between the nanopillars 2. Thus, unlike the isolated planar shallow junction type nano column solar cell of the emitter layer, the surface electrode 13 can be collected from the entire range of the emitter layer 11 when electrically connected to a portion of the emitter layer 11. Carrier. Accordingly, the solar cell of the first embodiment is a surface electrode 13 electrically connected to the emitter layer 11, and a laminated structure of Ag, Al, Ti, Pd, Ni, Cu, or the like can be used. The pattern electrode is formed.

Further, as described above, the nano-pillar 2 is formed of a p-type semiconductor and does not include an n-type emitter layer, so that the passivation film 12 can be bonded to the nano-pillar 2 and the emitter layer 11 . Setter.

Further, unlike the radial junction type nano column solar cell in which the emitter layer is required to be thinned, it is not necessary to form the emitter layer 11 as a thin film. Accordingly, the emitter layer 11 is made thicker, and the sheet resistance can be relatively reduced. Specifically, the film thickness of the emitter layer 11 can be, for example, 500 nm or more.

As described above, according to the solar battery cell of the first embodiment, compared with the conventional solar battery cell, the recombination loss inside the sub-wavelength structure can be reduced, and the pattern electrode can be used as the surface electrode.

<First Manufacturing Method>

3 is a view showing the first of the nano column solar battery cells of Example 1. Diagram of the manufacturing method. The method for producing a nanocolumn solar cell of the first embodiment is two methods for forming a different column. In the first production method, a nano column is formed by a growth method, and in the second production method, a nano column is formed by a processing method. Hereinafter, a first manufacturing method of the nanocolumn solar battery cell of the first embodiment will be described with reference to Fig. 3 . However, in the manufacturing method shown in FIG. 3, the structure of the back side, that is, the formation of the BSF layer 21 and the back surface electrode 22 is omitted. These two types of engineering can be performed in the same manner as the general solar cell manufacturing method.

First, a photoresist 31 is formed on the surface of the substrate 1. The upper view of the structure after formation is shown in Fig. 3(a), and the cross-sectional view is shown in Fig. 3(b). The photoresist 31 is first patterned on the substrate 1 and then patterned by photolithography. After the patterning, the range in which the photoresist 31 is not present becomes the range of the nano column 2 of the final solar cell structure. However, as shown in FIGS. 3(a) and 3(b), the range in which the surface electrode 13 is finally formed is not patterned, and it is preferable that the nanopillar 2 is not formed.

Next, the catalyst metal 32 is formed on the photoresist 31. The upper view of the structure after formation is shown in Fig. 3(c), and the cross-sectional view is shown in Fig. 3(d). The catalyst metal 32 is a structure which is necessary when the nano column 2 is grown as described later, and generally Cu, Au, Pt or the like is used. The formation of the catalyst metal 32 is performed by a vapor deposition method, a sputtering method, a CVD method, or the like.

Thereafter, the photoresist 31 and the catalyst metal 32 formed directly above the photoresist 31 are removed by the lift-off method. The upper view of the structure after removal is shown in Fig. 3(e), and the cross-sectional view is shown in Fig. 3(f). Lifting method As a result, a structure in which the patterned catalyst metal 32 is present is formed on the substrate 1. As a method of forming this structure, in the first embodiment, a method of removing the photoresist 31 is described, but there are also other methods as follows. That is, on the surface of the substrate 1, a method of forming the patterned catalyst metal 32 from the beginning is not formed without forming the photoresist 31. For forming the patterned catalyst metal 32, a vapor deposition method using a metal mask or a method of dispersing nano particles of a catalyst metal is used. For these methods, compared with the method described in Embodiment 1, the method of using the lift-off method has the advantage of shortening the number of projects and cost, but on the other hand, there is a possibility that the pattern size of the catalyst metal 32 is likely to occur. The problem of unevenness. The unevenness of the pattern size of the catalyst metal 32 is ultimately the unevenness of the pattern size of the nano-pillars 2. The selection by the lift-off method, or the formation of the patterned catalyst metal 32 from the beginning, should be considered to the extent that the unevenness of the pattern size of the nano-pillars 2 can be tolerated.

In addition, in the method of dispersing the nanoparticles of the catalyst metal, only in the range where the surface electrode 13 is finally formed as described above, the patterning is not performed, and the nanopillar 2 is not formed. Apply the following means. That is, it is necessary to additionally have a surface in which the nanoparticle which has not been patterned after dispersing the nanoparticles on the substrate 1 is removed, or the surface of the substrate 1 which is not subjected to patterning before the dispersion of the nanoparticles is adjusted. In the case of chemical properties, the dispersed nanoparticles are repelled as a process in which nanoparticles are not present in the range where they are not patterned. Accordingly, as a result of the method described above, there is a problem that the number of projects or the cost increases as a result of the method of dispersing the nanoparticles.

Next, the emitter layer 11 is formed. Along with this, in the range of the nano-pillar 2 in the process of FIG. 3(j), the portion joined to the emitter layer 11 (pn junction portion) is also formed and formed. The upper view of the structure after formation is shown in Fig. 3(g), and the cross-sectional view is shown in Fig. 3(h). The formation of the emitter layer 11 is performed by an impurity injection method such as a vapor phase diffusion method, a solid phase diffusion method, or an ion implantation method. Accordingly, the catalyst metal 32 serves as a catalyst for the growth of the nanocolumn 2, and also serves as a mask for the diffusion of impurities. Therefore, the relative positions of the nanopillar 2 and the emitter layer 11 are self-integratedly adjusted. However, when the emitter layer 11 is formed by the impurity implantation method, as described above, the catalyst metal 32 functions as a photomask, but the diffusion of the impurity injected into the substrate 1 is generally the same. Accordingly, in fact, the emitter layer 11 is formed partially on the lower portion of the catalytic metal 32, that is, the lower portion of the nanocolumn 2. When the lateral diffusion length of the emitter layer 11 is larger than the diameter of the nano-pillar 2, the structure in which the nano-pillar 2 and the substrate 1 are separated by the emitter layer 11 is formed. As described above, when the substrate 1 and the nano-pillar 2 are p-layers and the emitter layer 11 is an n ⁺ layer, the structure of the nano-pillar 2, the emitter layer 11, and the substrate 1 is a pn ⁺ p structure. The holes generated inside the nanopillar 2 are caused to be recombined in the emitter layer 11 before reaching the substrate 1. Thus, the substrate 1 and the nano-pillar 2 must be separated from each other by the emitter layer 11, and the lateral diffusion of the emitter layer 11 can be suppressed.

Thereafter, the catalyst metal 32 is used as a species, and the nanopillar 2 is formed by growing a portion (protrusion portion) of the nanopillar 2 that protrudes from the upper portion of the emitter layer 11. The above diagram of the structure after growth is shown in Figure 3. (i) The cross-sectional view is shown in Fig. 3(j). The growth of the nanocolumn 2 is carried out by a VLS (Vapor Liquid Solid) growth method or the like. It is known that Cu is used as the catalyst metal 32, and the nanocolumn having a small defect density is realized by performing VLS growth at a high temperature of about 1000 °C. However, in the case where the ion implantation method is used in the method of forming the emitter layer 11, the activation of ions can be performed by adding heat to the sample between the growth of the VLS, but at this time, as described above, Care must be taken not to carry out the lateral diffusion of the emitter layer 11 as much as possible.

Next, the catalyst metal 32 is removed. The upper view of the structure after removal is shown in Fig. 3(k), and the cross-sectional view is shown in Fig. 3(l). The removal of the catalyst metal 32 is carried out by wet etching according to the solution. At this time, the etching rate for the substrate 1, the column 2, and the emitter layer 11 is slow, that is, a solution having a high etching selectivity is preferably used.

Thereafter, the passivation film 12 is formed. The upper view of the structure after formation is shown in Fig. 3(m), and the cross-sectional view is shown in Fig. 3(n). The formation of the passivation film 12 may be performed by a film formation method such as a CVD method, a sputtering method, an epitaxial growth method, or a vapor deposition method, or the material of the passivation film 12 is a nano-pillar 2 and an emitter layer 11 In the case of an oxide or a nitride of a material, the passivation film 12 may be formed by surface oxidation or surface nitridation.

Finally, the surface electrode 13 is formed. The upper view of the structure after formation is shown in Fig. 3(o), and the cross-sectional view is shown in Fig. 3(p). The formation of the surface electrode 13 is performed by a film formation method such as a printing method, a vapor deposition method, a plating method, a sputtering method, or a CVD method. The surface electrode 13 and the emitter layer 11 are bonded to each other, and it is necessary to remove the passivation film 12 existing therebetween. The method of removing the passivation film 12 can be selected from a method of performing a method of photolithography and etching, using a method of etching an electric paste, and printing the surface electrode 13 and then firing it to electrically conduct it. . In the cross-sectional view of Fig. 3(p), the passivation film 12 directly under the surface electrode 13 is removed over the same width as the surface electrode 13, but the width of the removed passivation film 12 is taken as the width of the surface electrode 13. In the narrower case, the contact area of the emitter layer 11 and the surface electrode 13 may be reduced. The contact area between the emitter layer 11 and the surface electrode 13 is reduced, and the effect of recombination suppression is known. On the other hand, the contact resistance is increased, and it is necessary to consider the re-bonding and the contact resistance at two points. Area is optimized.

The above is the first manufacturing method of the solar battery cell of Example 1. This manufacturing method is characterized in that a metal pattern (catalyst metal 32) is used as a mask, and a second conductivity type (n-type) different from the first conductivity type is formed on the surface of the first conductivity type (p-type) substrate 1. The project of the emitter layer (Fig. 3(g)(h)), and the process of forming a plurality of nanopillars 2 on the surface of the substrate 1 using the same metal pattern (catalytic metal 32) (Fig. 3(i) ( j)).

According to the related feature, the first catalyst method can use the same catalyst metal 32 as a mask for forming the emitter layer, or can be used as a species for growing the nano column, thereby reducing the processing cost and reducing the processing cost. The relative positions of the nanopillar 2 and the emitter layer 11 can also be self-aligned. Further, in comparison with the second manufacturing method described later, in the first manufacturing method, any of the isotropic injection method and the anisotropic injection method may be used in forming the emitter layer 11. However, in addition to the above works, it is suitable for additional use. It is also possible to improve the crystallinity or film quality of each film, or heat treatment for improving the quality of the interface with the adjacent film, plasma treatment, and the like.

<Second Manufacturing Method>

4 is a view showing a second method of manufacturing the nanocolumn solar cell of Example 1. As described above, in the first production method, the nanocolumn 2 is formed by a growth method, but in the second production method, the nanocolumn 2 is formed by a processing method. Hereinafter, a second method of manufacturing the nanocolumn solar cell of the first embodiment will be described with reference to FIG. However, similarly to the first manufacturing method, the forming process of the structure on the back side is omitted.

First, an etching mask 33 is formed on the surface of the substrate 1. The upper view of the structure after formation is shown in Fig. 4 (a), and the cross-sectional view is shown in Fig. 4 (b). The etching mask 33 is a photomask for forming an etching process of the nanocolumn 2 in the next process, and metal nanoparticle, SiO ₂ , a photoresist, or the like is generally used as the material. In the case where metal nanoparticles are used, the etching mask 33 can be formed by dispersing the nanoparticles. Further, the etching of the metal may be performed by a lift-off method or an etching method to form the etching mask 33. For the case of using SiO ₂ or a photoresist, the etching mask 33 can be formed by patterning using photolithography.

Next, the surface of the substrate 1 is processed to form a portion (protrusion portion) which protrudes into the upper portion of the emitter layer 11 and then protrudes from the upper portion of the emitter layer 11. The upper view of the structure after formation is shown in Fig. 4(c), and the cross-sectional view is shown in Fig. 4(d). The formation of the protruding portion is performed by a method such as dry etching, wet etching, or laser evaporation. From the viewpoint of reflection prevention effect It is preferable that the aspect ratio of the nano-pillar 2, that is, the value of "height/diameter" is large, and it is preferable to form a protruding portion by dry etching using high processing anisotropy. Further, in order to increase the aspect ratio, it is also effective to use the etching mask 33 as a laminated structure of two or more layers.

Thereafter, the emitter layer 11 is formed. Along with this, the portion (pn junction portion) bonded to the emitter layer 11 among the nano-pillars 2 is also combined and formed. The upper view of the structure after formation is shown in Fig. 4(e), and the cross-sectional view is shown in Fig. 4(f). The formation of the emitter layer 11 is performed by the impurity injection method as in the first production method. However, unlike the first production method, the isotropic implantation method such as the vapor phase diffusion method cannot be used, and ion implantation must be used. The law of anisotropic injection of law. The reason for this is assumed to be that the emitter layer 11 is also formed on the side wall portion of the nano-pillar 2 when the impurity is injected by the isotropic injection method in the present process.

As the engineering system after the first, the structure shown in FIGS. 3(k) and (l) of the first manufacturing method 1 can be obtained by removing the etching mask 33, and thereafter, the history and the first manufacturing method are obtained. The same engineering can realize the nano column solar cell structure construction of Embodiment 1.

The above is the second manufacturing method of the solar battery cell of the first embodiment. This manufacturing method is characterized in that it has a process of forming a plurality of nano-pillars 2 on the surface of the substrate 1 by etching the etching mask 33 as a mask (Fig. 4(a)(b)), and via use. At the time of the anisotropic implantation method, a process of impregnating the surface between the substrate 1 and the plurality of columns 2 (Fig. 4(c)(d)) is injected.

The related embodiment 1 can also be manufactured through the related works. Solar battery unit. Further, in the second manufacturing method, the nano column 2 is formed by a processing method, and when a single crystal is used as the substrate 1, the nano column 2 formed by the processing method is the same as the first manufacturing method. The nano column 2 formed by the growth method is superior in terms of crystallinity or purity, and the recombination loss can be reduced.

Example 2

5(a) and 5(b) are a top view and a cross-sectional view of a solar battery cell according to a second embodiment of the present invention. The difference from Embodiment 1 is that the structure of Embodiment 1 is a nano-column solar cell, and the structure of Embodiment 2 is a nano-trench solar cell having a plurality of surfaces extending in a specific direction parallel to the surface of the substrate 1. The point of the unit of the convex portion 3. In the same manner as in the first embodiment, the top view and the cross-sectional view of the structure in which only the passivation layer 12 is removed from the nano-pillar solar cell structure of the second embodiment are shown in Figs. 6(a) and (b). 5 and 6 show a structure in which the cross-sectional shape perpendicular to the extending direction of the convex portion 3 and the surface of the substrate is a square shape. However, as described above, the convex portion 3 may have a different cross-sectional shape such as a triangle or a sector. .

As described above, the solar battery cell of the second embodiment is characterized in that the substrate 1 having the first conductivity type (p type) and the surface of the substrate 1 are of the first conductivity type and have a plurality of convexities extending in a specific direction. The portion 3 is provided on the surface of the substrate 1, and the second conductivity type (n-type) emitter layer 11 different from the first conductivity type, and the emitter layer 11 is provided between the plurality of convex portions 3.

According to the related features, as in the case of the first embodiment, the loss of recombination inside the convex portion 3 can be reduced. Further, as shown in the upper diagram of Fig. 6(a), the emitter layer 11 is continuous on the outer circumference of the plurality of convex portions 3. In this way, the emitter layers 11 are not isolated, and the entire surface of the substrate 1 is continuous. Thus, as in the first embodiment, the pattern electrodes can be used as the surface electrodes 13.

As described above, as in the case of the second embodiment, as in the case of the nano-column solar cell of the first embodiment, the re-bonding loss inside the convex portion 3 is also reduced in the nano-groove solar cell, and as the surface electrode 13 , and the pattern electrode can be used.

The manufacturing method of the structure of the second embodiment is the same as that of the first embodiment. However, as a method of forming the convex portion 3, a processing method is generally used. Subsequently, the structure of the nano-groove solar cell of Example 2 was produced by the same method as the second manufacturing method of the nano-column solar cell of Example 1. The point where the convex portion 3 is not formed in a portion of the surface of the substrate 1 described above can be realized by the pattern of the etching mask 33 designed in the second manufacturing method of the first embodiment.

Example 3

7(a) and 7(b) are a top view and a cross-sectional view of a solar battery cell according to a second embodiment of the present invention. Different from Example 1, the structure of Example 3 is a nanopore solar cell, and in the nanopore solar cell of Example 3, inside the sub-wavelength structure, that is, the sidewall of the nanopore 4. At the top of the range, the point where the emitter layer 11 is formed 2 of them. In the same manner as in the first embodiment, the top view and the cross-sectional view of the structure in which only the passivation layer 12 is removed from the nanocolumn solar cell structure of the third embodiment are shown in Figs. 8(a) and (b). 7 and 8 show a structure in which the nanopore 4 is a cylindrical recess. However, as described above, the nanopore 4 may be a columnar structure having a different cross-sectional shape. The nanopore solar cell structure of the third embodiment can be regarded as a structure in which a nanopore is used in place of a nanocolumn in the above planar shallow junction type nano column solar cell. However, the following differences were made between the nanopore solar cell unit of Example 3 and the planar shallow junction type nano column solar cell. That is, in the planar shallow junction type nano column solar cell, as described above, the emitter layer 11 formed on the top of the column 2 is isolated from each other, and as the surface electrode 13, it is not necessary to form a pattern electrode. In the comprehensive electrode. On the other hand, in the nanopore solar battery cell of the third embodiment, the shallow electrode layer 11 formed on the surface of the substrate 1 in which the nanopore 4 is not provided is as shown in the upper view of Fig. 8(a). The entire substrate 1 is entirely continuous, and as the surface electrode 13, a pattern electrode can be used.

As described above, the solar battery cell of the third embodiment has a substrate 1 having a plurality of columnar recesses (nano holes 4) on its surface and being of a first conductivity type (p type), and a substrate 1 disposed on the substrate 1 The surface of the second conductivity type (n-type) of the emitter layer 11 which is different from the first conductivity type is not included in the columnar recess, and the width of the columnar recess is 1 μm or less.

According to the relevant features, by the emitter layer 11 than the nanopore The height of 4 is used as a thin film, and the recombination loss of the solar cell in the nano hole can be reduced to the same extent as the planar shallow junction type nano column solar cell unit, and the planar shallow junction type nano column solar cell unit Unlike the surface electrode 13, a pattern electrode can be used. Specifically, the film thickness of the emitter layer 11 can be, for example, 500 nm or less.

As a manufacturing method of the structure of the third embodiment, first, the emitter layer 11 is formed over the entire substrate 1, and then the nanopore 4 is formed, and then the passivation film 12 and the surface electrode 13 are formed. The emitter layer 11 can also be formed by any method of impurity injection or film formation. The formation of the nanopore 4 is generally carried out by etching or by laser processing. The formation of the passivation film 12 can be carried out by surface oxidation or surface nitridation as in the case of Example 1, and may be carried out by a film formation method. In the case where the passivation film 12 is formed by the film formation method, when the nanopore 4 is viewed from above, the side wall of the nanopore 4 is not shaded, that is, the opening area at the top of the nanopore 4 is used as the bottom portion. It is preferred that the opening area is the same or a larger shape.

However, Patent Document 1 discloses a solar battery cell structure having a hole array structure as a surface reflection preventing structure and a shallow emitter layer formed on the side wall portion of the hole. This configuration is similar to the configuration of Embodiment 3, but there are differences between the two as follows. First, the diameter of the pores in the structure of Patent Document 1 is 1 μm or more, and the width of the nanopore to be used in the present invention is 1 μm or less. The width of the nanopore is defined as a diameter of 1 μm or less, which is defined as having the same diameter as the wavelength of sunlight or a finer diameter, and the sunlight is Among them, light having a wavelength of 1 μm or less is particularly strong, and in a solar battery cell, two points in a wavelength range generally used. Further, the structure of Patent Document 1 has a feature that the bottom portion is wider than the opening of the hole. It is assumed that in the nanopore solar cell, unlike the columnar recess of the third embodiment, when the area of the bottom portion is used as the shape of the opening portion of the nanopore, the opening portion as described in the third embodiment is used. When the area of the bottom is the same as the nanopore, the range between the bottom of the adjacent nanopore is narrowed and the series impedance is increased; the surface area of the nanopore increases and the surface recombination loss increases. In the case of the nanopore, there is a range of shadows, and as a surface passivation layer of a nanopore, it is difficult to use a film formation method such as a CVD method, and the above 3 The point becomes a topic. Accordingly, in the structure of Patent Document 1, it is difficult to make the diameter of the opening portion 1 μm or less.

When the above is the case, the hole array used in the structure of Patent Document 1 is of such a size, not a sub-wavelength structure. Further, in the structure of Patent Document 1, when the size of the opening of the hole is reduced to about 1 μm or less which is equivalent to the sub-wavelength structure, the series resistance is increased, the recombination loss is increased, and the film formation method is used. When the passivation film is difficult, the three points are a problem. The structure of Patent Document 1 is difficult if the diameter of the opening is 1 μm or less.

The invention described in Patent Document 1 and the invention according to the third embodiment are different in configuration and effect.

The invention made by the inventors of the present invention has been specifically described based on the embodiments, but the present invention is not limited to the foregoing implementation. For example, various changes can be made without departing from the scope of the content.

12‧‧‧ Passivation film

13‧‧‧ surface electrode

Claims (9)

A solar battery cell comprising: a plurality of pillars extending in a specific direction; and a substrate of a first conductivity type; and a second conductive layer different from the first conductivity type and bonded to the substrate In the emitter layer of the type, the plurality of pillar systems are formed of the first conductivity type semiconductor, and the plurality of pillar systems are joined to the emitter layer on the side surface thereof, and the emitter layer is in the plurality of pillars If the portion is not provided, the electrode is electrically connected to the emitter layer, and the electrode is made of Ag, Al, Ti, Pd, Ni, Cu, or the like. The film thickness of the electrode layer is 500 nm or more. The solar battery unit according to claim 1, further comprising a passivation film which is provided in combination with the plurality of pillars and the emitter layer. The solar battery unit according to claim 1, wherein the concentration of the impurity in the emitter layer is higher than the concentration of the impurity in the plurality of columns. The solar battery unit according to claim 1, wherein the plurality of columns have a width of 1 μm or less. A solar battery cell characterized by having a plurality of columnar recesses on a surface thereof, a first conductivity type substrate, and a portion provided on the surface of the substrate and not provided with the columnar recesses, and the foregoing The second conductivity type emitter layer having different conductivity types, wherein the columnar recess has a width of 1 μm or less, and further includes an electrode electrically connected to the emitter layer, wherein the electrode is made of Ag, Al, Ti, or Pd. In the case of a laminated structure of Ni, Cu, or the like, the film thickness of the emitter layer is 500 nm or less. The solar battery unit according to claim 5, wherein the concentration of the impurity in the emitter layer is higher than the concentration of the impurity in the plurality of columns. The solar battery unit according to claim 5, wherein a thickness of the emitter layer is smaller than a height of the columnar recess. A method for producing a solar battery cell, comprising: a first project of forming a second conductivity type emitter layer different from the first conductivity type on a surface of a first conductivity type substrate by using a metal pattern as a mask; And a second engineer who forms the plurality of pillars of the first conductivity type on the surface of the substrate by using the metal pattern, wherein the emitter layer is not provided for the plurality of pillars; Electrodes that are electrically connected to the pole layer, The electrode is made of Ag, Al, Ti, Pd, Ni, Cu, or the like. The method of manufacturing a solar battery cell according to the eighth aspect of the invention, wherein the second engineering system is to grow the plurality of pillars by using the metal pattern as a seed.