JP2014075418A - Silicon substrate for solar cell and manufacturing method therefor, and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon substrate for a solar cell in which combination of carriers and current leakage can be suppressed on the interface of a silicon substrate precursor, and to provide a manufacturing method therefor.SOLUTION: The silicon substrate for a solar cell has a planar silicon substrate precursor 101, and an aluminum oxide film 102 covering the side face 101c and two principal surfaces 101a, 101b of the silicon substrate precursor 101. The silicon substrate precursor 101 is composed of p-type silicon, and at least one of two principal surfaces 101a, 101b of the silicon substrate precursor 101 is shaped to have a texture.

Description

  The present invention relates to a silicon substrate for a solar cell, a manufacturing method thereof, and a solar cell.

  In recent years, solar cells have been increasingly and widely used from the viewpoint of effective use of natural energy. As a material constituting a solar cell, crystalline silicon has been mainly used so far.

  A solar cell using crystalline silicon is formed by joining n-type silicon and p-type silicon. By irradiating the crystalline silicon with light, a pair of electrons and holes is generated in the vicinity of the boundary (pn junction surface) between the two. Then, the generated electrons and holes can be captured by the electrodes connected to the n-type silicon and the p-type silicon, respectively, and a current due to the captured electrons and holes can be generated.

  That is, the crystalline silicon solar cell has a function of converting the energy of irradiated light into electric energy that can be output to the outside. In particular, crystalline silicon solar cells have a high rate of conversion to electrical energy (photoelectric conversion efficiency) in the energy of irradiated light, and occupy an important position in the solar cell market. Technological development is underway to enhance it.

  In order to further increase the photoelectric conversion efficiency of the crystalline silicon solar cell, it is important to suppress carrier recombination at the interface (Non-Patent Document 1). The carrier recombination here is that the unstable energy level (interface level), called dangling bonds that do not have adjacent atoms to be bonded, on the surface that is the terminal of the atomic arrangement This is a phenomenon in which the carriers generated in are captured and disappear. As a result, it is known that the number of carriers constituting the current extracted to the outside is reduced, and the characteristics of the solar cell are impaired.

Plasma Fusion Res. Vol. 85, no. 12 (2009) 820-824

  The present invention has been made in consideration of the above points. It is a first object of the present invention to provide a silicon substrate for a solar cell capable of suppressing carrier recombination at the interface of a silicon substrate precursor. The purpose.

  The present invention also provides a method for manufacturing a silicon substrate for a solar cell, in which an aluminum oxide film having a film thickness capable of tunneling carriers is formed on a side surface and two main surfaces of a planar silicon substrate precursor. Second purpose.

  A silicon substrate for a solar cell according to claim 1 of the present invention includes a flat silicon substrate precursor, and an aluminum oxide film covering a side surface and two main surfaces of the silicon substrate precursor, and the silicon substrate The precursor is made of p-type silicon, and at least one of the two main surfaces of the silicon substrate precursor has a textured shape.

  The silicon substrate for a solar cell according to claim 2 of the present invention is the silicon substrate for solar cell according to claim 1, wherein the aluminum oxide film is thicker on the side surface side of the silicon substrate precursor than on the two main surface sides of the silicon substrate precursor. It is the shape which has.

  The silicon substrate for a solar cell according to claim 3 of the present invention is the silicon substrate for solar cell according to claim 1 or 2, wherein the film thickness of the aluminum oxide film on each of the two main surfaces of the silicon substrate precursor is 0.5 [nm]. The above is 3 [nm] or less.

  According to a fourth aspect of the present invention, there is provided a method for producing a silicon substrate for a solar cell, wherein a flat tray provided with a through hole having a protrusion continuous with an inner surface is disposed in a film forming apparatus, and the through hole is provided. In the ALD, only one of the peripheral surfaces of the two main surfaces of the planar silicon substrate precursor having a texture formed on at least one main surface is supported by the protrusions. A first step of adsorbing trimethylaluminum molecules on the side surface and two main surfaces of the silicon substrate precursor using a method, and a second step of oxidizing the adsorbed trimethylaluminum molecules after the first step And an aluminum oxide film is formed on the side surface and two main surfaces of the silicon substrate precursor by repeating the process consisting of a plurality of times.

  The solar cell which concerns on Claim 5 of this invention is a solar cell which expresses a photoelectric conversion function between a light-receiving surface and the back surface facing this light-receiving surface, Comprising: In any one of Claims 1-3. The silicon substrate for solar cells described above, a semiconductor layer made of n-type amorphous silicon formed on the main surface of the silicon substrate for solar cells on the light receiving surface side, and formed on the light receiving surface side of the semiconductor layer A transparent conductive film, a light receiving surface electrode formed on the light receiving surface side of the transparent conductive film, and a back electrode formed on a main surface on the back surface side of the solar cell silicon substrate, It is characterized by that.

  According to the configuration of the silicon substrate for a solar cell according to the present invention, an aluminum oxide film having a negative fixed charge is formed on the substrate interface, thereby generating an electric field passivation effect and suppressing carrier recombination at the substrate interface. It is possible to provide a silicon substrate for a solar cell that can be used.

  Further, according to the configuration of the silicon substrate for a solar cell according to the present invention, the silicon substrate precursor is made of P-type silicon, and the aluminum oxide film forming the passivation film contains a lot of negative fixed charges. Therefore, the potential energy of electrons that are minority carriers is increased at the interface between the silicon substrate precursor and the aluminum oxide film, and the electrons are moved away from the interface. Therefore, it is possible to provide a silicon substrate for a solar cell that can suppress leakage of electrons (current) from the interface to the outside.

  In addition, according to the method for manufacturing a silicon substrate for a solar cell according to the present invention, a high-quality aluminum oxide film whose film thickness is controlled in molecular units is formed on the side surface and two main surfaces of the flat silicon substrate precursor. Can be formed. Therefore, the manufacturing method of the silicon substrate for solar cells which formed the aluminum oxide film | membrane of the film thickness which can tunnel a carrier on the side surface and two main surfaces of a flat silicon substrate precursor can be provided.

(A) It is sectional drawing of the silicon substrate for solar cells based on 1st embodiment. (B) It is an expanded sectional view of the edge part of the silicon substrate for solar cells based on 1st embodiment. It is a manufacturing process flow of a solar cell. It is sectional drawing of the manufacturing apparatus of the silicon substrate for solar cells which concerns on 1st embodiment. (A) It is a top view of the tray which supports the silicon substrate for solar cells. (B) It is the figure which expanded the one part upper surface among the trays which support the silicon substrate for solar cells. (C) It is the figure which expanded some cross sections among the trays which support the silicon substrate for solar cells. (A)-(d) It is a manufacturing-process figure of the silicon substrate for solar cells which concerns on 1st embodiment. (A), (b) It is sectional drawing of the solar cell based on the experiment example of 1st embodiment.

  Hereinafter, based on a preferred embodiment, the present invention will be described with reference to the drawings.

<First embodiment>
Fig.1 (a) is a figure explaining the structure of the silicon substrate 100 for solar cells which concerns on 1st embodiment. The silicon substrate 100 for solar cells includes a flat silicon substrate precursor 101, an aluminum oxide film 102 covering one main surface 101a, the other main surface 101b, and a side surface 101c other than both main surfaces of the silicon substrate precursor. It consists of.

  The silicon substrate precursor 101 is made of p-type single crystal silicon or p-type polycrystalline silicon, and one main surface 101a and the other main surface 101b have a textured shape. In the present embodiment, one main surface 101a and the other main surface 101b are respectively defined as surfaces that are located in the middle of the surfaces including the tops and the surfaces including the valleys that constitute the texture shape. .

  FIG.1 (b) is the figure which expanded the cross section of the area | region A by the side of one main surface 101a among the peripheral parts of the silicon substrate 100 for solar cells shown to Fig.1 (a). As shown in FIG.1 (b), one main surface 101a of a silicon substrate precursor is a surface located in the middle of the surface 101p containing each top part, and the surface 101v containing each trough part which comprise a texture shape. It has become. That is, the distance d1 between one main surface 101a and the surface 101p including each top is equal to the distance d2 between one main surface 101a and the surface 101v including each valley. The film thickness Ta of the aluminum oxide film 102 formed on the one main surface 101a side of the silicon substrate precursor is defined as the distance from each inclined surface constituting the texture shape to the surface of the aluminum oxide film 102.

  When the thickness of the aluminum oxide film 102 is smaller than 0.5 [nm], the passivation function for the interface of the silicon substrate precursor 101 cannot be maintained. Further, when the film thickness of the aluminum oxide film 102 is larger than 3 [nm], it is difficult to tunnel carriers. Therefore, the film thickness of the aluminum oxide film 102 is desirably 0.5 [nm] or more and 3 [nm] or less in the two main surfaces 101a and 101b, and is 1 [nm] or more and 2 [nm] or less. If so, it is more desirable.

  It is desirable that the aluminum oxide film 102 has a shape that is thicker on the side surface 101c side of the silicon substrate precursor 101 than on the two main surfaces 101a and 101b side. That is, in FIG. 1B, the film thickness Tc of the aluminum oxide film 102 formed on the side surface 101c side of the silicon substrate precursor is the aluminum oxide film formed on the one main surface 101a side of the silicon substrate precursor. It is desirable that the film thickness is larger than the film thickness Ta of 102.

  In addition, as 1st embodiment, although the two main surfaces 101a and 101b of the silicon substrate precursor showed both the shapes which have a texture, at least one of the two main surfaces 101a and 101b is shown. Any shape having a texture may be used. That is, only one of the two main surfaces 101a and 101b may be dry-etched, and only the processed surface may have a textured shape.

  As described above, according to the configuration of the solar cell silicon substrate 100 according to the first embodiment, since the interface of the silicon substrate precursor 101 is covered with the aluminum oxide film 102, carrier recombination can be suppressed. A possible silicon substrate 100 for a solar cell can be provided. And the solar cell which raised the photoelectric conversion rate can be obtained by using the silicon substrate 100 for solar cells which concerns on 1st embodiment.

  Further, according to the configuration of the solar cell silicon substrate 100 according to the first embodiment, the silicon substrate precursor 101 is made of P-type silicon, and the aluminum oxide film 102 forming the passivation film contains a lot of negative fixed charges. Yes. Therefore, the potential energy of electrons that are minority carriers is increased at the interface between the silicon substrate precursor 101 and the aluminum oxide film 102, and the electrons are moved away from the interface. Therefore, it is possible to provide the solar cell silicon substrate 100 capable of suppressing leakage of electrons (current) from the interface to the outside. And the solar cell which raised the photoelectric conversion rate can be obtained by using the silicon substrate 100 for solar cells which concerns on 1st embodiment.

<Method for producing silicon substrate for solar cell>
The manufacturing method of the silicon substrate for solar cells based on 1st embodiment is demonstrated. FIG. 2 is a manufacturing process flow of the solar cell. The solar cell is mainly composed of silicon substrate precursor (base) cleaning, aluminum oxide (Al ₂ O ₃ ) film formation (film formation), amorphous silicon film formation (film formation), transparent conductive film (ITO film) formation, It is manufactured by sequentially performing six process steps of forming an aluminum electrode and forming a silver electrode. The silicon substrate for solar cells according to the first embodiment is manufactured by sequentially performing the first two process processes, that is, the process of cleaning the silicon substrate precursor and the process of forming the aluminum oxide film. Below, the manufacturing method of the silicon substrate for solar cells which concerns on 1st embodiment is demonstrated in detail.

  First, in the silicon substrate precursor cleaning step, the silicon substrate precursor 101 is subjected to wet etching using potassium hydroxide (KOH) or sodium hydroxide (NaOH) as an etchant. Then, organic substances and metal contaminants remaining in the treated silicon substrate precursor 101 are removed using hydrofluoric acid to process the two main surfaces 101a and 101b into a textured shape.

FIG. 3 is a cross-sectional view of the film forming apparatus 10 for forming the aluminum oxide film 102 on the silicon substrate precursor 101. The film forming apparatus 10 includes a film forming chamber 11, a flat plate 103 that is disposed inside the chamber 11, forms a lower electrode for plasma formation, and supports the silicon substrate precursor 101, and the tray 103. A heater 13 for heating the silicon substrate precursor 101, a shower plate 17 for irradiating the silicon substrate precursor 101 with gas, and an upper electrode 18 for forming plasma are provided. The heater 13 is in contact with the tray 103. The shower plate 17 and the main surface of the tray 103 are arranged so that the main surfaces are parallel to each other. An exhaust hole 12, a trimethylaluminum (TMA) gas supply hole 14, a nitrogen (N ₂ ) gas supply hole 15, and an oxidizing agent (for example, H ₂ O) supply hole 16 are provided on the wall of the chamber. .

  An aluminum oxide film forming process using the film forming apparatus 10 of FIG. 3 will be described. 4A is a plan view of the tray 103 shown in FIG. 3 as viewed from the upper electrode 18 side. The tray 103 includes a plurality of structural portions R that support the silicon substrate precursor 101 in a fixed state. FIG. 4A shows a state in which the silicon substrate precursor 101 is removed in order to explain the shape of the tray 103.

  FIG. 4B is an enlarged view of a region B surrounding one of the plurality of structural portions R provided in the tray 103 of FIG. The structure portion R has a shape in which a through hole H penetrating between two main surfaces of the tray 103 is provided, and a protrusion 103 c continuous with the inner side surface 103 b is provided inside the through hole H. The surface of the protrusion 103 c on the side in contact with the silicon substrate precursor 101 is an inclined surface 103 a processed into a taper shape in the thickness direction of the tray 103. In addition, in the thickness direction of the tray 103, an angle formed by the inclined surface 103a and the inner surface 103b is an obtuse angle.

  4C is a diagram showing a cross section of the tray 103 included in the region B and the silicon substrate precursor 101 supported by the tray 103 taken along the line CC in FIG. 4B. is there. In the silicon substrate precursor 101, only the peripheral edge 101e of the other main surface 101b is supported by the inclined surface 103a of the protrusion 103c. In this state, a film forming process is performed on the silicon substrate precursor 101.

  By using the tray 103 described above, the side surface 101c of the silicon substrate precursor and the two main surfaces 101a and 101b are simultaneously exposed to the film forming gas when the film forming process is performed in the chamber 11. Therefore, the film forming process for the side surface 101c and the two main surfaces 101a and 101b of the silicon substrate precursor can be performed simultaneously. That is, when the film formation process is performed one surface at a time, a process of inverting the silicon substrate precursor 101 is required, but this process becomes unnecessary by using the tray 103 of this embodiment. Therefore, the apparatus structure can be simplified as compared with a case where a mechanism for inverting the silicon substrate precursor 101 is provided. In addition, the time required for inversion of the silicon substrate precursor 101 is reduced, and the film formation processing time can be shortened.

  Further, in the vicinity of the contact point between the side surface 101c of the silicon substrate precursor and the tray 103, the flow path of the film forming gas becomes narrow, so that the film forming gas tends to stay there. For this reason, the film formation rate is higher on the side surface 101c than on the two main surfaces 101a and 101b. Therefore, the aluminum oxide film 102 can have a shape having a thickness on the side surface 101 c side of the silicon substrate precursor 101 than on the two main surfaces 101 a and 101 b side of the silicon substrate precursor 101.

  A distance d4 between the inner side surfaces 103b facing each other of the through-hole H is formed to be larger than a distance d5 between the peripheral edge portions 101e facing each other on the main surface of the object to be processed. Further, the distance d3 between the tips 103e of the protrusions 103c facing each other in the through hole H is formed to be smaller than the distance d5 between the peripheral edges 101e facing each other on the main surface of the object to be processed. The protrusion 103c is formed at a certain depth from the main surface of the tray 103, and the two main surfaces 101a and 101b of the silicon substrate precursor and the main surface of the tray 103 are arranged in parallel to each other. Shall be.

  FIG. 4A shows an example in which the shape of the structure portion R is also square when the main surface of the silicon substrate precursor 101 is square, but the shape of the structure portion R is the silicon substrate precursor. Any shape that can include the main surface of the body 101 is acceptable, and the shape may not be square.

  The method of the film-forming process for manufacturing the silicon substrate for solar cells based on 1st embodiment is demonstrated using process drawing shown to Fig.5 (a)-(d). Note that the film formation process in the present embodiment is performed using the ALD method. First, the silicon substrate precursor 101 is placed on the tray 103 provided in the film forming chamber. Here, as described above, the silicon substrate precursor 101 is placed in the through hole H provided in the tray 103 and is supported by the protrusion 103 c on the inner side surface of the through hole H. 5A to 5D, the two main surfaces 101a and 101b of the silicon substrate precursor are both shown to be flat, but at least one of the two main surfaces 101a and 101b is The texture shape has a microscopic scale. During the film forming process, the temperature of the silicon substrate precursor 101 is desirably controlled in the range of 80 to 200 [° C.].

  In the first step, for example, 10 [SLC] of nitrogen gas is flowed into the chamber and the pressure is set to 300 [Pa], and then trimethylaluminum (TMA) gas is supplied at 1 [cc / cycle] per cycle. In 10 seconds, supply is made uniform in the chamber. Then, trimethylaluminum molecule Sa is adsorbed on the side surface 101c and the two main surfaces 101a and 101b of the silicon substrate precursor. After the adsorption, nitrogen gas is kept flowing for 10 seconds to purge (remove) the trimethylaluminum molecule Sa adsorbed excessively on the side surface 101c and the two main surfaces 101a and 101b of the silicon substrate precursor 101. After the purge, as shown in FIG. 5A, the trimethylaluminum molecule Sa adsorbed on the side surface 101c and the two main surfaces 101a and 101b of the silicon substrate precursor forms a layer close to a monomolecular layer.

  Next, in the second step, oxygen gas is introduced as an oxidation source, and oxygen ions and oxygen radicals generated by the RF discharge are supplied to the trimethylaluminum molecule Sa adsorbed on the substrate surface in the first step, thereby trimethylaluminum. The molecule Sa is oxidized to obtain a high-quality aluminum oxide film 102a. As an oxidation source of the trimethylaluminum molecule Sa, water or the like may be used in addition to ions or radicals obtained by ionizing oxygen gas.

  Next, in the third step, for example, 10 [SLC] of nitrogen gas is allowed to flow into the chamber and the pressure is set to 300 [Pa], and then trimethylaluminum (TMA) gas is supplied at 1 [cc / cycle], 1 Deliver uniformly within the chamber at 10 seconds per cycle. Then, the trimethylaluminum molecule Sb is adsorbed onto the aluminum oxide film 102a. After the adsorption, the nitrogen gas is allowed to flow for 10 seconds to purge (remove) the trimethylaluminum molecules Sb adsorbed excessively on the aluminum oxide film 102a. After the purge, as shown in FIG. 5C, the trimethylaluminum molecule Sb adsorbed on the aluminum oxide film 102a forms a layer close to a monomolecular layer.

  Next, in the fourth step, oxygen gas is introduced as an oxidation source, and oxygen ions and oxygen radicals generated by the RF discharge are supplied to the trimethylaluminum molecule Sb adsorbed on the substrate surface in the third step, thereby trimethylaluminum. The molecule Sb is oxidized to obtain a high-quality aluminum oxide film 102b. As the oxidation source of the trimethylaluminum molecule Sb, water or the like may be used in addition to ions or radicals obtained by ionizing oxygen gas.

  The process consisting of the third step and the fourth step is the same as the process consisting of the first step and the second step, respectively. FIG. 5 shows only four process diagrams corresponding to the first to fourth processes. However, in the fourth and subsequent processes, the process continues until the film thickness of the aluminum oxide film 102 reaches a desired film thickness. The process consisting of one step and the second step is repeated a plurality of times. By repeating the process consisting of the first step and the second step 5 to 25 times, the film thickness of the aluminum oxide film 102 has a passivation function with respect to the interface of the silicon substrate precursor 101, and enables carrier tunneling. The film thickness becomes (0.5 to 3 [nm]). By setting the number of repetitions to about 10 times, the aluminum oxide film 102 having an optimum film thickness (1 to 2 [nm]) can be obtained.

  As described above, according to the method for manufacturing the solar cell silicon substrate 100 according to the first embodiment, the film thickness is expressed in molecular units on the side surface 101c and the two main surfaces 101a and 101b of the planar silicon substrate precursor. It is possible to form a high-quality aluminum oxide film 102 controlled by the above. Accordingly, a method of manufacturing a silicon substrate for a solar cell is provided, in which an aluminum oxide film 102 having a thickness capable of tunneling carriers is formed on a side surface 101c and two main surfaces 101a and 101b of a planar silicon substrate precursor. Can do.

[Experimental example]
Fig.6 (a) is sectional drawing of the solar cell 110 formed using the silicon substrate 119 for solar cells which concerns on 1st embodiment. Solar cell 110 has a light receiving surface that receives light and a back surface that faces the light receiving surface. The solar cell silicon substrate 119 constituting the solar cell 110 includes an n-type semiconductor layer (n layer) 114, a transparent conductive film 115, and a light receiving surface electrode 117 on the light receiving surface side α of the solar cell 110. In order, a back electrode 116 is provided on the back side β of the solar cell 110.

  The silicon substrate 119 for solar cells includes a flat silicon substrate precursor 111, a main surface 111a on one side (light receiving surface side α) of the silicon substrate precursor, a main surface 111b on the other side (back surface side β), and both main surfaces The aluminum oxide film 112 covers the side surface 111c other than the surface. In FIG. 6A, the two main surfaces 111a and 111b of the silicon substrate precursor are shown to be flat, but at least one of the two main surfaces 111a and 111b is microscopic. It should have a texture shape with a large scale.

  The n layer 114 is made of n-type amorphous silicon, and is formed by sandwiching the aluminum oxide film 112 on one main surface 111a side of the silicon substrate precursor 111 by using PECVD (Plasma Enhanced CVD) method. The thickness of the n layer 114 to be formed is about 2 to 5 [nm].

  The transparent conductive film 115 is made of indium tin oxide (ITO), and is formed on the surface of the n layer 114 on the light receiving surface side α using the sputtering method after the n layer 114 is formed. The formed transparent conductive film 115 has a thickness of about 80 to 100 [nm].

  The back electrode 116 contains any element of Ag, Al, or Cu as a main component, and after forming the transparent conductive film 115, the other main surface 111b of the silicon substrate precursor 111 is formed using a sputtering method or a screen printing method. On the side, an aluminum oxide film 112 is sandwiched. The thickness of the back electrode 116 to be formed is about 200 to 500 [nm].

  Note that a layer made of an element such as Ti, W, Nb, Ni, or Cr may be provided between the back electrode 116 and the aluminum oxide film 112. This layer functions as a barrier layer for preventing the metal element constituting the back electrode 116 from diffusing to the aluminum oxide film 112 side, and as an adhesion layer for bringing the back electrode 116 and the aluminum oxide film 112 into close contact with each other. To do.

  The light receiving surface electrode 117 is made of Ag element, and is formed on the surface of the transparent conductive film 115 on the light receiving surface side α by performing baking using a screen printing method after forming the back electrode 116.

  FIG.6 (b) is sectional drawing of the solar cell 120 formed using the silicon substrate 129 for solar cells which concerns on 1st embodiment. The configuration in which the p-type semiconductor layer (p layer) 128 is provided on the back surface side β of the solar cell silicon substrate 129 is different from the configuration of the solar cell 110 in FIG.

  The p layer 128 is made of p-type amorphous silicon, and is formed by sandwiching the aluminum oxide film 122 on the other main surface 121b side of the silicon substrate precursor 121 by using PECVD (Plasma Enhanced CVD) method. The thickness of the formed p layer 128 is about 2 to 5 [nm]. In FIG. 6B, the two main surfaces 121a and 121b of the silicon substrate precursor are shown to be flat, but at least one of the two main surfaces 121a and 121b is microscopic. It should have a texture shape with a large scale.

  The p-type impurity concentration is higher in the p layer 128 than in the silicon substrate precursor 121. By providing the p layer having a high p-type impurity concentration between the back electrode 126 and the silicon substrate precursor 121, the electric field is weakened between the back electrode 126 and the silicon substrate precursor 121, and the electrical resistance is reduced. The The configuration except that the p-type semiconductor layer (p layer) 128 is provided on the back surface side β of the solar cell silicon substrate 129 is the same as the configuration of the solar cell 110 in FIG.

  By setting the aluminum oxide film 122 to a film thickness that allows carriers to tunnel, carriers generated in the silicon substrate precursor 121 tunnel through the aluminum oxide film 122 even if the wiring layer is not formed. The electrode 127 or the back electrode 126 can be reached. That is, in the solar cells 110 and 120 formed using the solar cell silicon substrate according to the first embodiment, it is not necessary to form the wiring layer, and in order to form the wiring layer, the aluminum oxide film 122 is formed. It is possible to reduce the process of providing an opening (contact hole) in the substrate and to simplify the process.

Table 1 shows the electrical characteristics of the solar cell when the thickness 119 of the aluminum oxide film constituting the solar cell 110 is changed to 0 [nm] (no film), 1.1 [nm], and 10 [nm]. The experimental results are summarized for the short-circuit current density J _sc , the open circuit voltage V _oc , the _fill factor FF, and the conversion efficiency E _ff ). The structure in which the aluminum oxide film 119 is not formed corresponds to the structure of a conventional solar cell.

According to the experimental results, when the thickness of the aluminum oxide film 119 is formed to 1.1 [nm], the short-circuit current density J _sc , the open-circuit voltage V _oc , and the _fill factor FF are compared to the case of the conventional configuration. As a result, the conversion efficiency _Eff is improved. This is because the aluminum oxide film 119 having a negative fixed charge is formed on the substrate interface, thereby generating an electric field passivation effect and suppressing carrier recombination at the substrate interface.

On the other hand, when the thickness of the aluminum oxide film 119 is set to 10 [nm], the short-circuit current density J _sc , the open-circuit voltage V _oc , and the _fill factor FF are significantly reduced as compared with the conventional configuration. As a result, the conversion efficiency E _ff decreases. This is because the aluminum oxide film 119 is too thick and carriers cannot tunnel. Therefore, in order to improve the characteristics of the solar cell, it is not desirable that the thickness of the aluminum oxide film covering the substrate be 10 [nm] or more.

  The method for producing the sample used in this experiment will be described below. First, a p-type silicon substrate is etched for 10 minutes using a solution of KOH (12% wt, 60 ° C., 0.6 g). Then, using a commercially available texture etching solution, a texture etching treatment is further performed for 30 minutes so that the reflectance (wavelength 400 to 800 [nm] average) becomes 12.56%.

  After the texture etching treatment, a rinsing treatment is performed for 3 minutes using pure water (25 ° C.). The substrate is immersed in a mixed solution of nitric acid: hydrofluoric acid = 100: 1 for 2 minutes to etch the interface of the substrate. Rinse for 3 minutes with water (25 ° C.). Then, the mixture is immersed in a solution (80 ° C.) in which hydrochloric acid, hydrogen peroxide solution, and pure water are mixed at a volume ratio of 1: 1: 5 for 5 minutes, and pure water (25 ° C.) is used for 3 minutes. A rinse treatment is performed, and finally, the substrate is immersed in a solution of HF (4% / wt) for 1 minute, followed by a rinse treatment for 3 minutes using pure water (25 ° C.) to prepare a silicon substrate for a solar cell used in the experiment.

Next, a film formation process of aluminum oxide by ALD is performed on the silicon substrate for solar cell. After evacuation so that the pressure in the chamber becomes 6.8 × 10 ⁻³ [Pa], nitrogen gas is flowed into the chamber for 2 [SLM], the pressure is set to 200 [Pa], and TMA gas is supplied. Is supplied at 2 [cc / cycle] for 1 second for 1 cycle, and then oxygen gas is supplied at 100 [sccm]. Then, 200 [W] is applied to an RF electrode having a frequency of 13.56 [MHz], and charged particles such as radicals, ions, and electrons are supplied to form an Al ₂ O ₃ monomolecular film. The above-described process (cycle purge) is performed to prepare a sample in which Al ₂ O ₃ is formed to a thickness of about 1.1 [nm], a sample in which the film is formed to 10 [nm], and a sample in which no film is formed. Here, the substrate temperature during the film forming process is set to 150 [° C.].

After an Al ₂ O ₃ passivation film is formed on both main surfaces of the substrate, an n-type amorphous silicon (na-Si) film is formed on the light-receiving surface side of the substrate by PECVD. The thickness of the na-Si film to be formed is 5 [nm] here. However, plasma pretreatment is performed before film formation.

In the plasma pretreatment, for example, H ₂ (300 [sccm]) and PH ₃ (5 [sccm]) are supplied into the chamber as the reaction gas, the pressure is set to 60 [Pa], and the frequency is set to 27. Plasma is generated at 12 [MHz], ES is 30 [mm], and power density is 10 [mW / cm ² ] for 30 seconds. Here, the substrate temperature during the plasma pretreatment is set to 150 [° C.].

In the film formation process using plasma, for example, H ₂ (200 [sccm]), PH ₃ (10 [sccm]), SiH ₄ (10 [sccm]) are supplied as reaction gases into the chamber, and the pressure is set to 80 [ After setting the frequency to Pa], the frequency is 27.12 [MHz], the ES is 35 [mm], the power density is 10 [mW / cm ² ], and plasma is generated for 180 seconds. Here, the substrate temperature during the film forming process is 150 [° C.].

Next, an ITO film is formed on the na-Si film formed on the light receiving surface side of the substrate by a sputtering method. Here, the thickness of the ITO film to be formed is 90 [nm]. In the film formation process, for example, oxygen gas (9 [sccm]) and Ar gas (50 [sccm]) are supplied as reaction gases, the ultimate pressure is 3.6 × 10 ⁻⁴ [Pa], and the film formation pressure is 0. After setting to 0.8 [Pa], the TS is set to 70 [mm] and the power density is set to 3.2 [W / cm ² ]. Here, SnO (10% wt) is used as a target for the sputtering treatment. The substrate temperature during the film forming process is 200 [° C.] here.

Finally, an Al electrode is formed on the back side of the substrate by sputtering. Here, the film thickness of the Al electrode to be formed is 500 [nm]. In the film formation process, for example, Ar gas (50 [sccm]) is supplied, the ultimate pressure is set to 3.7 × 10 ⁻⁴ [Pa], the film formation pressure is set to 0.9 [Pa], and the set temperature of the heater is set. The temperature is 100 [° C.], the power density is 3.2 [W / cm ² ], the specific resistance is 3.1 [Ω · cm], and the TS is 70 [mm].

  The present invention can be widely applied to the case where the photoelectric conversion efficiency of a solar cell using crystalline silicon is increased.

DESCRIPTION OF SYMBOLS 10 ... Film-forming apparatus, 100 ... Silicon substrate for solar cells,
101a, 101b ... main surface, 101c ... side surface, 101e ... peripheral edge,
102 ... aluminum oxide film, 103 ... tray, 103b ... inside surface,
103c ... projection, 110 ... solar cell, 114 ... semiconductor layer,
115: Transparent conductive film, 116: Back electrode, 117 ... Light receiving surface electrode,
H ... through-hole, Sa, Sb ... trimethylaluminum molecule.

Claims (5)

A planar silicon substrate precursor;
An aluminum oxide film covering a side surface and two main surfaces of the silicon substrate precursor,
The silicon substrate precursor is made of p-type silicon,
A silicon substrate for a solar cell, wherein at least one of the two main surfaces of the silicon substrate precursor has a textured shape.   The said aluminum oxide film is a shape which has thickness in the side surface side of the said silicon substrate precursor rather than two main surface sides of this silicon substrate precursor, The solar cell for Claim 1 characterized by the above-mentioned. Silicon substrate.   The film thickness of the said aluminum oxide film in two main surfaces of the said silicon substrate precursor is 0.5 [nm] or more and 3 [nm] or less, respectively, The Claim 1 or 2 characterized by the above-mentioned. Silicon substrate for solar cells. In the film forming apparatus, a flat tray provided with a through hole having a protrusion continuous with the inner surface is arranged,
In the through hole, a texture is formed on at least one main surface, and only one of the peripheral portions of the two main surfaces of the planar silicon substrate precursor is supported by the protrusion. As
Using ALD method,
A process comprising a first step of adsorbing trimethylaluminum molecules on the side surface and two main surfaces of the silicon substrate precursor, and a second step of oxidizing the adsorbed trimethylaluminum molecules after the first step. A method of manufacturing a silicon substrate for a solar cell, wherein an aluminum oxide film is formed on a side surface and two main surfaces of the silicon substrate precursor by repeating the above. A solar cell that expresses a photoelectric conversion function between a light receiving surface and a back surface facing the light receiving surface,
The silicon substrate for solar cells according to any one of claims 1 to 3,
A semiconductor layer made of n-type amorphous silicon, formed on the main surface of the solar cell silicon substrate on the light-receiving surface side;
A transparent conductive film formed on the light-receiving surface side of the semiconductor layer;
A light-receiving surface electrode formed on the light-receiving surface side of the transparent conductive film;
A back electrode formed on a main surface of the back surface side of the silicon substrate for solar cell.

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