JP4911878B2 - Semiconductor / electrode contact structure and semiconductor element, solar cell element, and solar cell module using the same - Google Patents

Description

  The present invention relates to a semiconductor / electrode contact structure with improved characteristics, a photoelectric conversion device such as a solar cell element, a semiconductor element such as a diode, a transistor, and a thyristor using the contact structure, and a solar having high efficiency characteristics. The present invention relates to a battery element and a solar battery module using the same.

  A semiconductor element generally has a contact portion between an electrode made of a conductive material such as a metal or a conductive oxide material and a semiconductor. A defect level generally called an interface state is generated on the semiconductor side of the semiconductor / electrode interface. Such a defect level is caused by impurities, strain, non-equilibrium in the process of forming the semiconductor, and functions as a carrier recombination center. Therefore, the semiconductor / electrode contact portion has a great influence on the characteristics of the semiconductor element. Effect.

  Carrier recombination at the semiconductor / electrode contact interface generally acts as a factor that deteriorates the current-voltage characteristics of the semiconductor element, and the recombination amount R at this interface is determined by the recombination center density Nr at the interface and the interface portion. Is proportional to the minority carrier density n.

R∝Nr × n

The recombination center density Nr is considered to be strictly in a relationship of Nr <Nd with the interface defect level density Nd. However, in the range handled in this case, there is almost no problem even if Nr≈Nd.

  Also, the variation in carrier recombination characteristics at this interface greatly affects the yield of semiconductor elements. Therefore, in order to improve the characteristics and yield of the semiconductor element, it is important to sufficiently reduce the carrier recombination amount R at the semiconductor / electrode contact interface.

  Hereinafter, a solar cell that is a representative of the photoelectric conversion device will be described as an example.

  Generally, a solar cell has a pn junction or a pin junction made of a semiconductor, and there are two types of electrodes: an electrode that contacts a p-type semiconductor and an electrode that contacts an n-type semiconductor. FIG. 4 shows the band diagram. In the figure, Ec is the energy position below the conduction band, Ev is the energy position above the valence band, Ed is the defect level on the semiconductor side (interface defect level) at the semiconductor / electrode interface, and Ef is the Fermi level. .

  FIG. 3 shows an example of a solar cell element structure when a pin junction is used among the two junctions. In FIG. 3, 1 is a substrate, 2 is a first electrode as a front electrode, 3 is a semiconductor multilayer film, 3a is a p-type semiconductor layer, 3b is an i-type semiconductor layer, 3c is an n-type semiconductor layer, and 4 is a back electrode. This is the second electrode.

  Here, light enters from the substrate 1 side and is absorbed and photoelectrically converted by the semiconductor multilayer film 3 to generate electron-hole pairs. However, in the case of the pin junction type as in this example, it is particularly photoactive. Electron-hole pairs generated by absorption and photoelectric conversion in the i-type semiconductor layer 3b serving as a layer are the main source of photovoltaic power. The generated electrons and holes (photoexcited carriers) are directed in the direction of the n-type semiconductor layer 3c and the holes are directed in the direction of the p-type semiconductor layer 3a according to the built-in electric field formed in the i-type semiconductor layer 3b. As a result of sweeping, the n-type semiconductor layer 3c has excess electrons and the p-type semiconductor layer 3a has excess holes, and a forward bias voltage is generated with respect to the pin-type junction. Excess carriers flow out to the electrodes, and current flows through the circuit connecting the solar cell and the load. The product of these forward bias voltage and current is the output photovoltaic power.

  Here, the presence of defect levels mainly at the semiconductor / electrode interface (in this example, the first electrode 2 / p-type semiconductor layer 3a and the n-type semiconductor layer 3c / second electrode 4) Two factors can adversely affect solar cell characteristics.

  The first factor is deterioration (increase) of diode characteristics (in the case of a solar cell, an increase in so-called dark current). This is due to the generation of the recombination current at the interface, and the increase in the dark current due to this causes a decrease in the open circuit voltage Voc and a decrease in the fill factor FF as solar cell characteristics.

  The second factor is a decrease in photocurrent. This is because the photoexcited carriers generated in the semiconductor region are recombined and lost at the interface, leading to a decrease in the short circuit current density Jsc as a solar cell characteristic.

  For these problems, there is a measure to highly dope the semiconductor interface region in the semiconductor / electrode contact. This is a method of utilizing the fact that the minority carrier density n is generally reduced in the highly doped portion, so that the recombination amount R at the interface is reduced. This is generally called an HL (High-Low) junction. It is. In particular, this technique is sometimes called a BSF structure because of the historical background of the effect (BSF effect = Back Surface Field effect) when formed on the back side of a solar cell (see, for example, Non-Patent Document 1).

  According to this method, the minority carrier density n can be reduced, but there is no principle reason why the recombination center density Nr due to the interface defect level can be expected to be reduced. On the contrary, it is considered that the recombination center density Nr at the interface generally increases because the amount of strain increases and defect generation occurs and the semiconductor quality generally decreases as the doping amount increases.

Here, it is considered that the maximum value of the interface defect level density is given by the DB density when all the bonds in the interface become dangling bonds (DB). For example, in the case of Si, the DB density at this time is a very large value of about 1 × 10 ¹⁵ / cm ² , and the recombination center density Nr is also a very large value of almost the same order.

  As described above, since the recombination amount R at the interface is proportional to the product of the minority carrier density n and the recombination center density Nr, even if the minority carrier density n can be reduced, the recombination center density Nr cannot be reduced ( On the contrary, if it increases on the contrary, the recombination amount R cannot be reduced sufficiently.

Actually, the reduction of the interface recombination amount R by this method is not sufficient for further improving the efficiency of the solar cell. For example, a further ultrathin SiO ₂ film is formed between the HL junction and the electrode. Development of technology for reducing the Nr is also carried out by interposing a material (for example, see Non-Patent Document 2). However, even in this improved method, it is not easy to form a high quality SiO ₂ film for reducing Nr sufficiently thinly, and high quality SiO ₂ film formation requires a high temperature process. Has a problem that various limitations on the process occur even in the case of a bulk type Si solar cell, and it cannot be applied to a thin film Si solar cell which is a low temperature process.

  There is also a method of widening the band gap of the interface region portion on the semiconductor side in the semiconductor / electrode contact. Since the minority carrier density n generally decreases in the wide gap portion, the recombination amount R at the interface decreases.

Historically, in an amorphous silicon solar cell using hydrogenated amorphous silicon (a-Si: H), a p-type layer in contact with a surface electrode (a transparent conductive film such as SnO ₂ ) is formed by hydrogenated amorphous silicon carbide (a-SiC). : H, band gap≈2.0 eV), and an example in which a heterojunction is formed with an a-Si: H (band gap≈1.8 eV) I-type layer as a photoactive layer is well known ( For example, refer nonpatent literature 2).

  Even in this method, the minority carrier density n can be reduced, but there is no guarantee that the defect level density Nr at the interface will not increase. In addition, since wide gaps generally lead to not only a reduction in minority carrier density n but also a reduction in majority carriers, if a wide gap is too wide, the flow of majority carriers is hindered, and this is a requirement on the premise. The ohmic characteristics of the semiconductor / electrode that has been used will be impaired. Therefore, there was a limit to the wide gap.

Here, a solar cell has been described as an example of a photoelectric conversion device among semiconductor elements. However, the principle characteristic of the above-described problem (recombination of carriers due to the presence of interface defect levels) is a semiconductor / electrode contact. Common to semiconductor devices having For example, in a diode, if the recombination amount R of the semiconductor / electrode contact portion is large, it causes a decrease in current-voltage characteristics such as a rise characteristic due to an increase in dark current. In a transistor, current-voltage characteristics such as on / off characteristics deteriorate. It becomes a factor of.
JP-A-2-76266 JP-A-2-76267 JP 2001-313272 A JP 2003-173980 A Basics and applications of thin-film solar cells (Ohm, 2001), p53-55 MAGreen et all, Proc. 15th IEEE PVSC (1981) p1405 Amorphous silicon (Ohm Co., 1993), p227

  As described above, in order to reduce the carrier recombination amount R at the semiconductor / electrode contact interface that deteriorates the current-voltage characteristics of the semiconductor element, the recombination center density Nr at the interface and the minority carrier density n at the interface part are set. Attempts to reduce each have been made, but there is a problem that if one of them is reduced, the other increases, and the obtained effect has a limit.

  The inventors have repeated experiments and studied in view of the above problems, and as a result, the recombination center density Nr can be reduced without increasing the minority carrier density n. As a result, the semiconductor / electrode contact interface can be reduced. The structure which can reduce the amount R of carrier recombination R in effectively was found. Then, the principle of the essence behind the phenomenon was clarified and the present invention was achieved.

  In view of the above, an object of the present invention is to provide a semiconductor / electrode contact structure in which the amount of carrier recombination R at the contact interface is reduced, and to provide a semiconductor element with improved characteristics by using this semiconductor / electrode contact structure. There is.

  Another object of the present invention is to provide a solar cell element having high conversion efficiency and a solar cell module using the same by applying the semiconductor element having the above-described improved characteristics to the solar cell element. is there.

  Patent Documents 1 and 2 disclose a semiconductor structure having a configuration similar to that of the present invention. Specifically, in a photoelectric conversion element formed by laminating a translucent substrate, a transparent electrode, a p-type semiconductor thin film, an i-type semiconductor thin film, an n-type semiconductor thin film, and a back electrode in this order, the transparent electrode and p In this configuration, an n-type semiconductor thin film (a highly conductive n-type semiconductor thin film or an n-type microcrystalline thin film) is interposed between the type semiconductor thin films.

  However, in this prior invention, since the principle has not been elucidated, the invention has been limited to an invention in which an n-type semiconductor is interposed in a very limited structure of a transparent electrode / p-type semiconductor contact structure. That is, no study has been made on the semiconductor / metal electrode contact structure and the n-type semiconductor / electrode contact structure in the present invention, which will be described later. Therefore, the solar cell characteristics according to the technique disclosed in this prior invention are not studied. The improvement was still inadequate.

  Specifically, even in the conventional structure before the prior invention, since the transparent conductive film is usually n-type, it is not necessary to intervene between the transparent conductive film and the p-type semiconductor, particularly without interposing the n-type layer of the prior invention. N / p reverse junction is formed. Therefore, even if an n-type layer is further interposed in this part, the improvement in characteristics is not so great. And what actually caused the problem was recombination at the interface between the n-type semiconductor and the backside metal electrode, and since this portion had not been improved at all, the improvement in characteristics was only slight. It was. The degree to which recombination at the contact interface can be suppressed is also related to the yield. This is also a particularly important recombination at the interface between the n-type semiconductor and the back surface metal electrode in the prior invention. Since no measures were taken to reduce the yield, sufficient yield improvement could not be realized.

  In order to achieve the above object, the inventors have repeatedly conducted thorough experiments and considerations, and as a result, a semiconductor exhibiting reverse conductivity between a semiconductor (for example, p-type) and an electrode at the semiconductor / electrode contact interface. It has been found that the amount of carrier recombination at the contact interface can be effectively reduced when a semiconductor satisfying a certain condition is interposed while interposing (in this example, n-type).

In view of the above, according to the semiconductor / electrode contact structure of the present invention, in a contact portion between a semiconductor having one conductivity type and an electrode, the conductivity opposite to that of the one conductivity type semiconductor is provided between the one conductivity type semiconductor and the electrode. The concentration of the doping element in both semiconductors in the region where these semiconductors (one-conductivity-type semiconductor and reverse-conductivity-type semiconductor) are in contact is set to be 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ^21. / Cm ³ or less. Thereby, the junction between the one-conductivity-type semiconductor and the reverse-conductivity-type semiconductor can be a tunnel junction or a junction having characteristics equivalent thereto, and a good ohmic property can be realized between the semiconductor / electrode.

Further, the semiconductor / electrode contact structure of the present invention has a conductivity type opposite to the one-conductivity type semiconductor between the one-conductivity-type semiconductor and the electrode at the contact portion between the one-conductivity-type semiconductor and the electrode. In the region where the opposite conductivity type semiconductor is interposed and these semiconductors (one conductivity type semiconductor and the opposite conductivity type semiconductor) are in contact with each other, the doping element concentration in the one conductivity type semiconductor and / or the opposite conductivity type semiconductor is set to a predetermined thickness d1. , D2 may be 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less. Thereby, the junction between the one-conductivity-type semiconductor and the reverse-conductivity-type semiconductor can be a tunnel junction or a junction having characteristics equivalent thereto, and a good ohmic property can be realized between the semiconductor / electrode.

  Further, the predetermined thickness d1 is preferably not less than one atomic layer and not more than the total thickness of the reverse conductivity type semiconductor, and the predetermined thickness d2 is not less than one atomic layer and not more than the total thickness of the one conductivity type semiconductor. desirable. Further, it is desirable that the thickness of the reverse conductivity type semiconductor is not less than one atomic layer and not more than 5 nm. As a result, the tunneling probability of carriers from one conductivity type semiconductor to the electrode through the reverse conductivity type semiconductor can be improved, and the ohmic property between the semiconductor and the electrode can be further improved.

  Furthermore, it is desirable that the reverse conductivity type semiconductor contains an element that expands the band gap of the semiconductor. In particular, it is desirable to contain at least one element selected from the group consisting of carbon, oxygen, and nitrogen. Thereby, since the minority carrier concentration can be further reduced, the recombination amount at the semiconductor / electrode interface can be further reduced by combining with the structure of the present invention. Further, since the expansion of the band gap also reduces the amount of light absorption in the reverse conductivity type layer, the effect of reducing the light absorption loss in this layer can also be obtained.

  And it is desirable for the reverse conductivity type semiconductor to contain a region for reducing the absorption coefficient of the semiconductor. This region is desirably a crystal-containing phase, particularly a phase containing an indirect transition type crystal. As a result, it is possible to achieve better tunnel junction or equivalent junction characteristics at the reverse junction while suppressing light absorption.

  Further, in the semiconductor / electrode contact structure of the present invention, if the electrode is made of a metal material, it can be applied not only to solar cells but also to general semiconductor devices. In particular, if the low resistance of the metal material is used, it can be suitably used for the surface collecting electrode portion in the bulk Si solar cell. Further, if the electrode is made of a transparent conductive material, light is not shielded, so that it can be suitably used as an electrode that transmits light particularly in a photoelectric conversion device or the like.

  Furthermore, if the electrode has a two-layer structure of a transparent conductive material layer and a metal material layer, and the transparent conductive material layer is positioned on the contact surface side with the semiconductor, the metal material component is contained by the transparent conductive material layer. The phenomenon of diffusing into the semiconductor layer and degrading the characteristics of the semiconductor element can be suppressed.

  Furthermore, the semiconductor element of the present invention has a plurality of semiconductor / electrode contact portions, and at least one of them has the semiconductor / electrode contact structure of the present invention. Thereby, since the semiconductor element of this invention can reduce the recombination amount in a semiconductor / electrode contact part, it can acquire the outstanding electric current-voltage characteristic (High conversion efficiency in a solar cell).

  Therefore, the solar cell element of the present invention using such a semiconductor element of the present invention is excellent with high conversion efficiency. Furthermore, the solar cell module of the present invention is a solar cell module having a plurality of solar cell elements that are electrically connected to each other, the solar cell of the present invention being included in the plurality of solar cell elements. Since the element is included, a solar cell module having high conversion efficiency is obtained.

  By the way, the reason why the present invention has the above-described operation and effect is presumed as follows.

  In the semiconductor / electrode contact structure of the present invention, a semiconductor (for example, p-type) having a reverse conductivity (an n-type in this example) is interposed between the semiconductor (for example, p-type) and the electrode, and n having the reverse conductivity is present. In order to realize a good ohmic property between the semiconductor and the electrode, the junction between the p-type semiconductor and the p-type semiconductor needs to be a tunnel junction or a junction having characteristics equivalent thereto.

Here, the junction having the junction characteristics according to the tunnel junction is a value ((V / I) × S, S is the area of the reverse junction) expressed as a surface resistance value in the VI characteristic of the reverse junction. In the applied voltage range of about −0.02 V to about 0.02 V applied to the reverse junction, it means a case of about 1 Ω · cm ² or less. For example, when the area S of the reverse junction is 1 cm ² and the current I flowing when the applied voltage is −0.02 V is −0.04 A, the sheet resistance value is 0.5 Ω · cm ² , If the current I flowing when the applied voltage is +0.02 V is 0.06 A, the sheet resistance value is 0.33 Ω · cm ² , but these sheet resistance values are within the required range of the junction characteristics (1 Ω · cm ² or less). ) Therefore, it can be said that the reverse junction having such a VI characteristic is a junction having a junction characteristic according to a tunnel junction suitable for the present invention.

  A band diagram of the conventional pin type semiconductor device shown in FIG. 3 is shown in FIG. The carrier recombination amount R at the semiconductor / electrode interface is a value proportional to the product of the minority carrier density n at this interface and the recombination center density Nr caused by the interface defect level Ed.

  On the other hand, FIG. 6 shows a structural diagram of a pin type semiconductor element to which the present invention is applied, and FIG. 2 shows a band diagram of the pin type semiconductor element having the same structure. Between the p-type semiconductor layer 3a and the electrode 2, there is an n-type semiconductor layer 6 that forms a tunnel junction with the p-type semiconductor layer 3a or a junction having characteristics equivalent thereto, and the n-type semiconductor layer 3c and the electrode 4 A p-type semiconductor layer 7 is provided between the n-type semiconductor layer 3c and the n-type semiconductor layer 3c to form a tunnel junction or a junction having characteristics equivalent thereto.

  In the semiconductor element of the present invention to which such a semiconductor / electrode contact structure in which a reverse-conductivity type semiconductor is interposed between the one-conductivity type semiconductor / electrode, the defect state density Nd itself at the semiconductor / electrode interface is the conventional element. However, the recombination center density Nr, which is the recombination center of minority carriers corresponding to the minority carriers of the conventional pin type semiconductor device, is greatly reduced.

  The reason is that in the conventional structure, the defect level Ed at the semiconductor / electrode interface is located on the minority carrier side with respect to the Fermi level Ef in the conventional element (see FIG. 4), and most of them function as recombination centers. To do. On the other hand, in the element to which the present invention is applied, the defect level Ed at the semiconductor / electrode interface is positioned on the majority carrier side with respect to the Fermi level Ef by interposing a reverse conductivity type semiconductor at the semiconductor / electrode interface. This is because most of them do not function as recombination centers (see FIG. 2).

  For example, in contrast to electrons that are minority carriers in a p-type semiconductor layer, the defect level Ed is in a state in which almost no electrons exist in the conventional device as shown in FIG. 4, so the recombination loss of minority carriers is very high. Although it occurs with efficiency, in the element to which the present invention is applied, the interface defect level Ed to be a recombination partner corresponding to the minority carrier is almost filled with electrons as shown in FIG. There is little recombination loss of minority carriers.

  That is, according to the present invention, the recombination center density Nr at the semiconductor / metal contact interface can be remarkably reduced as compared with the conventional semiconductor element. For this reason, the recombination amount R can be significantly reduced. Therefore, the device characteristics can be improved (the results shown in Table 1 are because the Jsc improvement is due to the reduction of the recombination loss of photoexcited carriers at the semiconductor / electrode interface, and the Voc improvement is due to the semiconductor / electrode interface). This can be interpreted as a decrease in the dark current component at the same time).

  In addition, since the recombination amount R can be greatly reduced to a level sufficiently exceeding a certain threshold value, a high yield can be obtained.

The reason why the doping concentration in the reverse junction is 1 × 10 ^{18 to} 5 × 10 ²¹ cm ⁻³ is to make the reverse junction a tunnel junction or a junction having a junction characteristic equivalent thereto. As a result, the ohmic property between the semiconductor and the electrode is not impaired.

As described above, in the present invention, in a contact portion between a semiconductor having one conductivity type and an electrode, a reverse conductivity having a conductivity type opposite to that of the one conductivity type semiconductor is provided between the one conductivity type semiconductor and the electrode. And a doping element concentration in both semiconductors in a region where the one-conductivity-type semiconductor and the reverse-conductivity-type semiconductor are in contact with each other is set to 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less. In addition to being able to effectively reduce the amount of minority carrier recombination at the semiconductor / electrode contact interface, it is possible to maintain good ohmic characteristics by forming tunnel junctions or junctions with similar characteristics. When the semiconductor / electrode contact structure of the present invention is applied, the characteristics of the semiconductor element can be dramatically improved.

  In addition, since the recombination amount is greatly reduced beyond a certain threshold, the yield of semiconductor elements can be improved. And especially the conversion efficiency of the solar cell element which is representative of a photoelectric conversion apparatus can be improved, and the solar cell module using this solar cell element also has high conversion efficiency.

  Embodiments of a semiconductor / electrode contact structure and a semiconductor device using the same according to the present invention will be described below in detail with reference to the drawings.

  As a first embodiment of a semiconductor device according to the present invention, a super straight type thin film Si solar cell in which light shown in FIG. 1 is incident from the substrate side will be described.

  In FIG. 1, 1 is a translucent substrate made of glass, 2 is a first electrode made of a transparent conductive film as a surface electrode, 3 is a semiconductor multilayer film made of Si-based material, and 31 is a first electrode made of Si-based material. 1 is a semiconductor junction layer, 32 is a second semiconductor junction layer made of Si-based material, 31a is a p-type semiconductor layer in the first semiconductor junction layer made of Si-based material, and 31b is a first semiconductor layer made of Si-based material. A photoactive layer in the semiconductor junction layer, 31c is an n-type semiconductor layer in the first semiconductor junction layer made of Si-based material, 32a is a p-type semiconductor layer in the second semiconductor junction layer made of Si-based material, 32b Is a photoactive layer in the second semiconductor bonding layer made of Si-based material, 32c is an n-type semiconductor layer in the second semiconductor bonding layer made of Si-based material, and 4 is a back electrode made of metal. Electrode.

  FIG. 7 is a band diagram of the thin film Si solar cell shown in FIG. FIG. 8 is a band diagram unified with the Fermi level Ef (the state after each layer is in contact). Ec is a conduction band edge, Ev is a valence band edge, Eg is a band gap, and Ed is a semiconductor / electrode interface state. In each figure, “μc-Si: H” indicates microcrystalline silicon, “a-Si: H” indicates hydrogenated amorphous silicon, and “a-SiC: H” indicates hydrogenated amorphous silicon carbide. In each drawing, these materials are shown for each layer, but this is only one typical example, and as will be described later, the material of each layer is not necessarily limited to these examples.

In the present invention, an n-type semiconductor layer 31d made of a Si-based material, which is a semiconductor layer of reverse conductivity type, is provided between the first electrode 2 and the p-type semiconductor layer 31a in the first semiconductor junction layer. In addition, a p-type semiconductor layer 32d made of a Si-based material, which is a semiconductor layer of opposite conductivity type, is provided between the second electrode 4 and the n-type semiconductor layer 32c in the second semiconductor junction layer. It is said. Each of these reverse conductivity type semiconductor layers has a doping element concentration of 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ , and forms a tunnel junction or a junction having characteristics equivalent thereto with the semiconductor layer in contact with the semiconductor layer. ing.

  With the semiconductor / electrode contact structure of the present invention, the electrical characteristics of the first electrode 2 and the p-type semiconductor layer 31a in the first semiconductor junction layer, as well as the second electrode 4 and the second semiconductor junction layer. The electrical characteristics with the n-type semiconductor layer 32c in the middle are greatly improved by the above-described effects of the present invention.

  That is, as shown in FIG. 8, the n-type semiconductor layer 31d provided between the first electrode 2 and the p-type semiconductor layer 31a in the first semiconductor junction layer, and the second electrode 4 and the second electrode 4 The p-type semiconductor layer 32d provided between the semiconductor junction layer and the n-type semiconductor layer 32c causes the defect level Ed at the semiconductor / electrode interface to be positioned on the majority carrier side with respect to the Fermi level Ef. Become. As a result, since most of these defect levels do not function as recombination centers, the amount of minority carrier recombination can be remarkably reduced at these semiconductor / metal interfaces, and good VI characteristics can be obtained. A semiconductor device having the same can be realized. Therefore, in terms of solar cell characteristics, the problem described in the problem section is solved, and an improvement in the open circuit voltage Voc and an improvement in the short circuit current density Jsc can be realized. Accordingly, the yield can be greatly improved.

  Hereinafter, the process for forming the thin film Si solar cell element of the present invention will be described.

  First, a translucent substrate is prepared as the substrate 1. Specifically, a plate material or a film material made of glass, plastic, resin, or the like can be used. For example, in the case of glass, so-called blue plate glass (soda lime glass) or white plate glass (borosilicate glass) having a thickness of about several millimeters can be used. In addition, for plastics and resins, materials can be selected as long as there is no problem in heat resistance and degassing properties in a later process.

  Next, the 1st electrode 2 which is a surface electrode is formed. As a material for the electrode, a material having a low conductive resistance and whose characteristics do not change for a long time can be selected. In particular, in the case of the 1st electrode 2 which is a surface electrode formed in a thin film solar cell, it is set as a transparent conductive film from a translucent viewpoint.

As a material of the transparent conductive film, known materials such as SnO ₂ , ITO, ZnO can be used. The transparent conductive film is exposed to a hydrogen gas atmosphere caused by the use of SiH ₄ and H ₂ when a Si film is subsequently formed on this film, so that ZnO is excellent in reduction resistance. It is desirable to form the film at least as the final surface.

  As the film forming method, known techniques such as CVD, vapor deposition, ion plating, sputtering, spraying, and sol-gel method can be used. Among them, productivity, large area film forming characteristics, and high quality can be used. It is desirable to use a CVD method or a sputtering method because a product can be obtained.

  The film thickness of the transparent conductive film is adjusted in the range of about 60 to 600 nm in consideration of the antireflection effect and low resistance. As a standard for lowering the resistance, it is desirable that the sheet resistance is about 10 Ω / □ or less.

  Next, a semiconductor multilayer film 3 made of a silicon film is formed. The semiconductor multilayer film 3 has a structure in which a first semiconductor bonding layer 31 and a second semiconductor bonding layer 32 are stacked. Here, as a method for forming a silicon-based film, a conventionally known PECVD method (Plasma Enhanced CVD method) or Cat-CVD method (Catalytic CVD method) can be used. By using the Cat-PECVD method disclosed in Document 3, Patent Document 4, etc., a high-quality film can be formed at high speed. In addition, if the Cat-PECVD method is used, crystallization can be greatly accelerated, and therefore, the formation of a crystalline film among the films described below is particularly effective.

  First, a first semiconductor junction layer 31 including a hydrogenated amorphous silicon film as a photoactive layer is formed as a top cell into which light first enters. Specifically, the n-type layer 31d / p-type layer 31a / photoactive layer 31b / n-type layer 31c are stacked in this order from the substrate side, and the photoactive layer 31b is i-type (intrinsic semiconductor). desirable.

  Next, a second semiconductor junction layer 32 including a crystalline silicon film as a photoactive layer is formed as a bottom cell. Specifically, the p-type layer 32a / photoactive layer 32b / n-type layer 32c / p-type layer 32d are formed in this order from the substrate side, and the photoactive layer 32b is preferably i-type.

  As described above, the semiconductor multilayer film 3 is formed by combining the first semiconductor junction layer 31 including the hydrogenated amorphous silicon film in the photoactive layer and the second semiconductor junction layer 32 including the crystalline silicon film in the photoactive layer. The reason for using it is that it becomes a top cell by utilizing the fact that hydrogenated amorphous silicon has a high light absorption characteristic especially for short wavelength light and the crystalline silicon film has a high light absorption characteristic even for long wavelength light. This is because the first semiconductor bonding layer 31 efficiently photoelectrically converts the short wavelength light and the second semiconductor bonding layer 32 serving as the bottom cell efficiently converts the long wavelength light.

In this specification, “crystalline silicon” is a concept including microcrystalline silicon (μc-Si: H... Microcrystalline silicon) and nano (crystalline) silicon (nc-Si: H... Nanocrystalline silicon). These microcrystalline silicon and nanosilicon include a crystalline phase and an amorphous phase of silicon, which are crystal-containing phases. The crystallization rate defined by the Raman scattering spectrum (crystal phase peak intensity / (crystal phase peak intensity + amorphous phase peak intensity)) is in the range of 50 to 100%. It will be in the range of ~ 80%. In the case of silicon, the crystalline phase peak intensity, a peak intensity at a peak intensity + 520 cm ^-1 in 500～510Cm ^-1, also an amorphous phase peak intensity may be a peak intensity at 480 cm ^-1 .

  Next, a manufacturing process of the first semiconductor bonding layer 31 will be described. In the first semiconductor junction layer 31, the semiconductor / electrode contact structure of the present invention is obtained by forming the n-type layer 31d between the first electrode 2 and the p-type layer 31a.

  The n-type layer 31d according to the semiconductor / electrode contact structure of the present invention uses a hydrogenated amorphous silicon film or a crystalline silicon film (microcrystalline silicon film or nanosilicon film) containing the crystalline silicon phase described above. it can. Here, hydrogenated amorphous silicon exhibits a direct transition-type high light absorption characteristic, whereas crystalline silicon exhibits an indirect transition-type relatively low light absorption characteristic. Therefore, in order to reduce light absorption loss, crystalline silicon is used. It is more preferable to use a crystalline silicon film containing a phase.

  In addition, since crystalline silicon has a narrower band gap than hydrogenated amorphous silicon, a crystal can be formed in order to form a tunnel junction or a junction having characteristics equivalent thereto with a p-type layer 31a described later. It is more preferable to use a quality silicon film. In addition, it is not necessary to make the crystalline silicon phase over the entire n-type layer 31d, and there may be a case where only the vicinity of the interface with the p-type layer 31a described later may be used. In this way, the light absorption loss in the narrow band gap region can be reduced as much as possible.

  Here, an impurity is doped in order to obtain an n-type. In order to obtain an n-type in a silicon semiconductor, P, As, Sb, or the like can be used as a doping element, among which P is desirable.

Then, the doping element concentration is 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ or more, and a substantial n ⁺ type is formed, so that a tunnel junction with the p-type layer 31a to be formed later or a characteristic equivalent thereto. Can be formed. This doping concentration need not be realized over the entire region of the n-type layer 31d, and may be formed at least in a region in contact with the p-type layer 31a. Specifically, the film thickness d1 at the location where n ⁺ is provided is at least one atomic layer or more and less than or equal to the film thickness as shown in the pin junction semiconductor element of the present invention in FIG. Good.

  The film thickness of the n-type layer 31d is about 20 nm or less, more preferably 10 nm or less, and the light absorption loss and resistance loss in this layer are reduced as much as possible. More preferably, by setting the thickness to 5 nm or less, if the n-type layer 31d itself can tunnel carriers, the resistance loss due to the n-type layer 31d can be made almost zero, and the ohmic characteristics are hardly lowered. No semiconductor / electrode contact can be obtained.

As a raw material for producing the n-type layer 31d, it can be formed using a gas such as SiH ₄ , H ₂ , and PH ₃ which is a doping gas. Here, since P is taken into the film almost in proportion to the partial pressure ratio of the PH ₃ gas and the SiH ₄ gas, the partial pressure ratio (specifically, the gas flow ratio) corresponding to the target doping concentration should be adjusted. A desired doping concentration can be realized. Moreover, what is necessary is just to adjust film-forming time according to a film-forming speed | rate about a film thickness. Furthermore, in particular, in order to crystallize, in the substrate temperature range of about 100 to 400 ° C. at which hydrogen deposition on the film forming surface is realized, the plasma excitation frequency is set to a VHF region of about 40 MHz or more, or gas heating is actively performed. This can be easily realized.

Furthermore, if an appropriate amount of a gas containing C (carbon) such as CH ₄ is mixed in addition to these gases, a Si _x C _1-x film can be obtained, and light absorption loss is reduced by expanding the band gap. In addition to being very effective for formation, it is also effective for reducing the dark current component for improving the open circuit voltage. At this time, if the C content is about 5 to 20%, the band gap expansion amount can be about 0.1 to 0.3 eV. The C content in the film is determined by the plasma power in consideration of the CH ₄ gas / SiH ₄ gas partial pressure ratio (that is, the gas flow ratio) in the film formation and the decomposition efficiency of CH ₄ and SiH ₄ being different. If adjusted, the desired value can be obtained. In addition to C, a gas containing O (oxygen) or a gas containing N (nitrogen) may be mixed in an appropriate amount to obtain a Si _x O _1-x film or a Si _x N _1-x film, Similar effects can be obtained. These may be mixed.

  Next, a p-type layer 31a is formed on the n-type layer 31d. As the p-type layer 31a, a hydrogenated amorphous silicon film, a crystalline silicon film containing a crystalline silicon phase represented by a microcrystalline silicon film, or the like can be used. Here, in order to form a tunnel junction or a junction having characteristics similar to the tunnel junction with the n-type layer 31d, it is more preferable to use a crystalline silicon film having a small band gap. Of course, it is not necessary to make the crystalline silicon phase over the entire p-type layer 31a, and only the vicinity of the interface with the n-type layer 31d may be used. In this way, the light absorption loss in the narrow band gap region can be reduced as much as possible.

  Here, impurities are doped in order to obtain p-type. In order to obtain a p-type in a silicon semiconductor, B, Al, Ga, or the like can be used as a doping element, among which B is desirable.

The doping element concentration is about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ and is substantially p ⁺ type. This doping concentration does not need to be realized over the entire p-type layer 31a, but may be formed at least in a region in contact with the n-type layer 31d. Specifically, if the film thickness d2 of the p ⁺ portion is realized in the range of at least one atomic layer and less than the film thickness as shown in the pin junction type semiconductor element of the present invention in FIG. Good.

  The thickness of the p-type layer 31a is adjusted in the range of about 2 to 100 nm depending on the material. For example, when a hydrogenated amorphous silicon material is used, the range is set to about 2 to 20 nm especially considering reduction of light absorption loss, and when a crystalline silicon material is used, 10 to 100 nm is considered in consideration of a decrease in junction forming ability. A range of about.

If an appropriate amount of a gas containing C (carbon) such as CH ₄ is mixed in addition to a gas such as SiH ₄ and H ₂ used for film formation and B ₂ H ₆ which is a doping gas, the Si _x C _1-x film is formed. It is obtained and is very effective for forming a window layer with little light absorption loss, and is also effective for reducing a dark current component for improving an open circuit voltage. In addition to C, the same effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen). Here, the preferable C content and its realization method are omitted since they are substantially the same as those in the case of the n-type semiconductor layer 31d.

  Next, a photoactive layer 31b that is a non-doped layer that is not doped is formed on the p-type layer 31a. A hydrogenated amorphous silicon film is used for the photoactive layer 31b. In practice, the non-doped film usually shows a slight n-type characteristic. In this case, the non-doped film can be adjusted so as to be substantially i-type by slightly containing a p-type doping element.

  In addition, in order to efficiently photoelectrically convert incident light, the current is matched between the top cell (first semiconductor bonding layer 31) and a bottom cell (second semiconductor bonding layer 32) to be described later. Is adjusted to a range of about 0.1 to 0.5 μm.

  Here, as a method for forming a hydrogenated amorphous silicon film, a conventionally known PECVD method or Cat-CVD method can be used. If the Cat-PECVD method is used, a high-quality hydrogenated amorphous silicon film is used. Can be formed at a high speed, a large area, and with high productivity, and is particularly effective for manufacturing a high-efficiency and low-cost thin-film Si solar cell.

  Further, according to the Cat-PECVD method, the hydrogen concentration in the film can be reduced to 15 atomic% or less by the atomic hydrogen generation promoting effect or the gas heating effect, but more preferably, it is difficult to realize by the conventional PECVD method. Since a film having a low hydrogen concentration of 10 atomic% or less, more preferably 5 atomic% or less can be obtained, it is possible to reduce the degree of photodegradation, which has been a problem with hydrogenated amorphous silicon film utilizing elements for many years.

  Next, an n-type layer 31c is formed on the photoactive layer 31b. As the n-type layer 31c, a hydrogenated amorphous silicon film or a crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) can be used, and the film thickness is adjusted in the range of about 2 to 100 nm depending on the material. . For example, when a hydrogenated amorphous silicon material is used, the range is set to about 2 to 20 nm especially considering reduction of light absorption loss, and when a crystalline silicon material is used, considering a decrease in junction forming ability, The range is about 100 nm.

The doping element concentration is about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ and is substantially n ⁺ type.

A Si _x C _1-x film can be obtained by mixing an appropriate amount of a gas containing C (carbon) such as CH ₄ in addition to gases such as SiH ₄ and H ₂ used for film formation and PH ₃ as a doping gas. Therefore, it is possible to form a film with little light absorption loss and to reduce dark current components for improving the open circuit voltage. In addition to C, the same effect can be obtained by mixing an appropriate amount of a gas containing O (oxygen) or a gas containing N (nitrogen).

In order to further improve the junction characteristics, a substantially i-type non-single-crystal Si layer or non-layer is formed between the p-type layer 31a and the photoactive layer 31b or between the photoactive layer 31b and the n-type layer 31c. A single crystal Si _x C _1-x layer may be inserted as a buffer layer. The thickness of the insertion layer at this time is about 0.5 to 50 nm. At this time, if the so-called graded layer is formed by inclining the hydrogen concentration or C concentration in the film, the amount of recombination in this region can be reduced.

  Here, in order to realize good ohmic characteristics, an n-type layer 31c and a p-type layer 32a, which are junctions between the first semiconductor junction layer 31 and the second semiconductor junction layer 32 described later, are also tunnel junctions. Or it is set as the joining which has the characteristic according to it. The realization method is the same as that already realized between the n-type layer 31d and the p-type layer 31a. Further, as described above with respect to the contact portion, the n-type layer 31d and the p-type layer 31a also desirably have a crystalline silicon phase in each layer.

  By the above method, the first semiconductor junction layer 31 can be formed as a top cell. Further, the second semiconductor bonding layer 32 is stacked thereon as a bottom cell, but the description of the portions that can be formed by the same method as the first semiconductor bonding layer 31 is omitted, and characteristic portions are described.

  In the second semiconductor junction layer 32, the n-type layer 32c / p-type layer 32d has the semiconductor / electrode contact structure of the present invention.

  As the second semiconductor bonding layer 32, first, a p-type layer 32 a is formed on the first semiconductor bonding layer 31. As this layer, a hydrogenated amorphous silicon film or a crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) can be used similarly to the p-type layer 31a in the first semiconductor junction layer described above. Detailed conditions such as film thickness and doping concentration are also the same and will not be described.

  Next, a photoactive layer 32b that is a non-doped layer that is not doped is formed on the p-type layer 32a. In the first semiconductor junction layer 31, the photoactive layer 31b is formed of a hydrogenated amorphous silicon film, but the photoactive layer 32b in the second semiconductor junction layer 32 is a crystal typified by a microcrystalline silicon film. It should be a quality silicon film.

  In practice, the non-doped film usually shows a slight n-type characteristic. In this case, the non-doped film can be adjusted so as to be substantially i-type by slightly containing a p-type doping element.

  The film thickness is adjusted within a range of about 1 to 3 μm in order to efficiently photoelectrically convert incident light and simultaneously match the current between the top cell and the bottom cell.

  Furthermore, as a film structure, the surface shape after film formation as an aggregate of (110) -oriented columnar crystal grains generated as a result of preferential growth of the (110) plane among the crystal planes is a self-generated structure suitable for optical confinement. It is desirable to have a concavo-convex structure, but if PECVD or Cat-PECVD is used, there is an advantage that this structure can be formed spontaneously (naturally).

  Here, as a method for forming a crystalline silicon film, a conventionally known PECVD method or Cat-CVD method can be used, but if a Cat-PECVD method is used, a particularly high-quality crystalline silicon film is formed. Since the film can be formed at high speed, large area, and high productivity, it is particularly effective for the production of a high-efficiency and low-cost thin-film Si solar cell.

  According to this Cat-PECVD method, a crystalline silicon film having a hydrogen concentration in the film of 10 atomic% or less can be obtained by the atomic hydrogen production promoting effect or the gas heating effect, more preferably 5 atomic% or less, A film having a low hydrogen concentration of preferably 3.5 atomic% or less can be obtained.

The reason why the low hydrogen concentration film is preferable is as follows. In the case of a crystalline silicon film, most of the hydrogen is present at the grain boundary, and the bonding state and density of hydrogen with Si are the quality of the grain boundary (the reciprocal of the carrier recombination rate at the grain boundary). To be proportional). That is, as the density of SiH ₂ bonds, which is a state in which two H atoms and two other Si atoms are bonded to one Si atom existing in the grain boundary, the higher the density of the so-called post-oxidation phenomenon (the film becomes atmospheric after film formation). When exposed to the atmosphere, gas components containing oxygen such as O ₂ , CO ₂ , and H ₂ O in the atmosphere diffuse, adsorb and oxidize at the crystal grain boundaries in the film, and change the bonding state of the crystal grain boundaries. The film quality of the entire film due to the deterioration of the quality of the crystal grain boundary (that is, the deterioration of the characteristics over time) is caused. Here, when the hydrogen concentration in the film is lowered, the SiH ₂ bond density at the crystal grain boundary is also reduced accordingly, so that the deterioration with time due to the post-oxidation phenomenon described above can be reduced.

  Specifically, when the hydrogen concentration in the film is 5 atomic% or less, the deterioration rate with time can be suppressed to about several percent or less, and when the hydrogen concentration in the film is 3.5 atomic% or less, the deterioration rate with time is almost zero. can do. As a result, a more efficient solar cell can be manufactured.

  Next, an n-type layer 32c is formed on the photoactive layer 32b. As this layer, a hydrogenated amorphous silicon film or a crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) can be used similarly to the n-type layer 31c in the first semiconductor junction layer. Detailed conditions such as film thickness and doping concentration are also the same and will not be described.

  In order to further improve the junction characteristics, a substantially i-type non-single-crystal Si layer is inserted between the p-type layer 32a and the photoactive layer 32b or between the photoactive layer 32b and the n-type layer 32c. Also good. The thickness of the insertion layer at this time is about 0.5 to 50 nm.

  As the second semiconductor bonding layer 32, the p-type layer 32d according to the present invention is formed. As this layer, a hydrogenated amorphous silicon film or a crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) can be used similarly to the n-type layer 31d in the first semiconductor junction layer described above. The difference from the n-type layer 31d is that only doping elements and B, Al, Ga, etc. exhibiting p-type conductivity are used, and the other conditions are the same for detailed conditions such as film thickness and doping concentration. is there.

  Finally, a metal film is formed as the second electrode 4 which is the back electrode. As the metal film material, it is desirable to use a material mainly composed of Al, Ag, or the like, which has excellent conductive characteristics and light reflection characteristics. By using these metal materials, it is possible to reflect the long wavelength light reaching the back electrode with a high reflectivity and effectively re-enter the semiconductor layer.

  As the film forming method, known techniques such as vapor deposition, sputtering, ion plating, and screen printing can be used, and sputtering is performed because productivity, large area film forming characteristics, and high quality can be obtained. It is desirable to use the method. Further, it is desirable that the film thickness be 0.1 μm or more in order to sufficiently reduce the electric resistance, and 1 μm or less in order to avoid an increase in cost.

  Note that the second electrode preferably has a structure in which a transparent conductive film / a metal film are stacked in this order from the side in contact with the semiconductor layer. Thus, by inserting the transparent conductive film between the semiconductor layer and the metal film, the phenomenon that the metal film component diffuses into the semiconductor layer and deteriorates the device characteristics can be suppressed.

  In addition, if an appropriate uneven structure is provided on the surface of the transparent conductive film, light is effectively scattered, so that the light confinement effect effective for improving the efficiency of the solar cell can be enhanced. Such a concavo-convex structure can be formed by the conditions at the time of film formation or by an etching process after film formation, and the maximum height Rmax of the concavo-convex at the interface between the transparent conductive film and the metal film is 0.05 μm or more. Adjust to.

Here, SnO ₂ , ITO, ZnO, or the like can be used as the transparent conductive film material, but ZnO is desirable for reasons such as ease of low-temperature formation, stability, and ease of realizing the concavo-convex structure. Further, at this time, the metal film to be laminated is preferably Ag.

  In addition, as a film forming method, known techniques such as CVD, vapor deposition, ion plating, sputtering, spray, and sol-gel can be used, but productivity, large area film forming characteristics, and high The sputtering method is desirable because a quality product can be obtained.

  By the above-described method, a thin film Si solar cell to which the present invention is applied can be realized.

  In the above description, the solar cell in which the semiconductor / electrode contact structure of the present invention is applied to both the first electrode side and the second electrode side of the semiconductor multilayer film has been described. Needless to say, the effect of the present invention can be obtained even when applied only to the second electrode side.

  Further, the tandem solar cell having two semiconductor junctions in the semiconductor multilayer film has been described. However, a single junction solar cell (not shown) having one semiconductor junction or a triple junction having three semiconductor junctions is described. The same effect can be obtained in a solar cell of a type (not shown) and a multi-junction type solar cell (not shown) having a larger number of semiconductor junctions.

  Furthermore, the solar cell having a structure in which different semiconductor bonding layers (the first semiconductor bonding layer and the second semiconductor bonding layer) are in direct contact with each other has been described. The same effect can be obtained for a solar cell (not shown) having a structure in which a very thin metal film or an alloy film with Si is inserted as an intermediate layer.

  Further, although the solar cell in which the semiconductor junction layer pin is formed in the order of pin from the light receiving surface side has been described, the same effect can be obtained also in the solar cell formed in the order of nip from the light receiving surface side.

  The super straight type solar cell in which light enters from the substrate side has been described, but the same effect can be obtained for a substrate type solar cell (not shown) in which light enters from the semiconductor film side. In the case of the substrate type, the substrate is not limited to the light-transmitting substrate, and a light-impermeable substrate such as stainless steel may be used. In this case, it is desirable that the first electrode be a metal material and the second electrode be a light-transmitting material.

  Next, FIG. 5 shows a bulk Si solar cell as a second embodiment to which the present invention is applied. In the figure, 501 is a surface electrode, 502 is an antireflection film, 503 is a p-type Si region, 504 is an n-type Si region, 505 is a p-type Si photoactive region, 506 is a p-type Si-BSF region, and 507 is an n-type. An Si region 508 is a back electrode.

As a structure of the present invention, a p-type Si region 503 that is a semiconductor of reverse conductivity type is provided between the front electrode 501 and the n-type Si region 504, and the back electrode 508 and the p-type Si-BSF region 506 are An n-type Si region 507, which is a semiconductor having a reverse conductivity type, is provided therebetween. Each of these reverse conductivity type semiconductors has a doping element concentration of 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ , and forms a junction having a semiconductor junction with each of them and a junction having characteristics equivalent thereto. Yes.

  Here, light enters from the antireflection film 502 side and is absorbed and photoelectrically converted in the Si region to generate electron-hole pairs. Electron-hole pairs generated by absorption and photoelectric conversion in the p-type Si photoactive region 505 serving as a layer are the main sources of photovoltaic power. Hereinafter, the principle until the photovoltaic power is generated is the same as that of the above-described thin film Si solar cell, and the description thereof will be omitted.

  Hereinafter, a process for forming the bulk Si solar cell according to the present invention shown in FIG. 5 will be described.

First, a p-type Si substrate is prepared. In FIG. 5, at least the p-type Si photoactive region 505 is included in the substrate. At this time, it is desirable to use B as the p-type doping element, and the concentration is about 1 × 10 ¹⁶ to 1 × 10 ¹⁷ / cm ³ (the specific resistance value of the substrate is about 0.2 to 2 Ω · cm at this time). Becomes).

  The substrate thickness is 500 μm or less, more preferably 350 μm or less. As a substrate type, a single crystal Si ingot made by slicing a single crystal Si ingot made by a manufacturing method such as CZ method or FZ method, or a multi-crystal slicing a polycrystalline Si ingot cast by a cast method to make a substrate A crystalline Si substrate or the like can be used. In addition, doping may include an appropriate amount of a doping element at the time of manufacturing the Si ingot, or may include an appropriate amount of B-containing Si lump whose doping concentration is already known.

Next, an n-type Si region 504 is formed. P is preferably used as the n-type doping element, and the doping concentration is set to about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ (that is, n ⁺ type in particular). As a result, a pn junction is formed between the p-type Si region 505 described above.

As a manufacturing method, it is formed by diffusing a doping element on the surface of the p-type Si substrate at a temperature of about 700 to 1000 ° C. using a thermal diffusion method using POCl ₃ (phosphorus oxychloride) as a diffusion source. At this time, the thickness of the diffusion layer is about 0.2 to 0.5 μm, and this can be set to a desired thickness by adjusting the diffusion temperature and the diffusion time.

  In a normal diffusion method, a diffusion region is also formed on the surface opposite to the target surface, but this portion may be removed later by etching. Alternatively, as will be described later, when the BSF layer on the back surface is formed of an Al paste, Al that is a P-type dopant can be diffused to a sufficient depth at a sufficient concentration, so that it has already been diffused. The influence of the n-type diffusion layer in the region can be neglected.

  Note that the method of forming the n-type Si region 504 is not limited to the thermal diffusion method. For example, a hydrogenated amorphous silicon film or a crystal can be formed using the thin film technology and conditions described in the first embodiment. A crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) may be formed at a substrate temperature of about 400 ° C. or lower.

  Here, when an n-type Si region is formed using a hydrogenated amorphous silicon film, the thickness is 50 nm or less, preferably 20 nm or less, and when formed using a crystalline silicon film, the thickness is 500 nm or less, Preferably it is 200 nm or less.

  At this time, if an i-type Si region (not shown) having a thickness of 20 nm or less is formed between the p-type Si region 505 and the n-type Si region 504, it is effective for improving the characteristics. However, when forming using thin film technology, it is necessary to consider the temperature of each process described below and to determine the order of formation so that the process temperature is as low as the subsequent process.

Next, a p-type Si-BSF (Back Surface Field) region 506 is formed. B or Al can be used as the p-type doping element, and the doping element concentration is set to about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ (that is, p ⁺ type in particular). As a result, a Low-High junction can be formed between the p-type Si photoactive region 505 and the p-type Si-BSF region.

As a manufacturing method, it can be formed at a temperature of about 800 to 1100 ° C. using a thermal diffusion method using BBr ₃ as a diffusion source. In the case of Al in particular, an Al paste made of Al powder and glass frit, an organic solvent, a binder, and the like. Can be applied by a printing method and then heat treated (baked) at a temperature of about 700 to 850 ° C. to diffuse Al (referred to as a paste printing and baking method in this specification), which is very advantageous for cost reduction. It is. When the p-type Si-BSF region 506 (back surface side) is formed by a thermal diffusion method, a diffusion barrier such as an oxide film is previously formed on the n-type Si region 504 (front surface side) already formed. Keep it. When using the paste printing firing method, it is possible not only to form a desired diffusion layer only on the printing surface, but also as described above, n formed on the back side simultaneously with the formation of the n-type Si region 504 region. There is no need to remove the mold layer.

  Note that the method for forming the p-type Si region 506 is not limited to the thermal diffusion method or the paste printing and firing method. For example, the hydrogenated amorphous silicon film is formed using the thin film technology and conditions described in the first embodiment. Alternatively, a crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) may be formed at a substrate temperature of about 400 ° C. or lower. At this time, the film thickness is about 10 to 200 nm. At this time, if an i-type Si region (not shown) having a thickness of 20 nm or less is formed between the p-type Si region 505 and the n-type Si region 504, it is effective for improving the characteristics. However, when forming using thin film technology, it is necessary to consider the temperature of each process described below and to determine the order of formation so that the process temperature is as low as the subsequent process.

  Next, in the contact structure of the semiconductor / electrode of the present invention on the front side, before forming the front electrode 501 on the n-type Si region 504, a p-type Si region 503 is interposed between these regions. Form. At this time, a tunnel junction or a junction having junction characteristics equivalent to the tunnel junction is formed and manufactured under the conditions described below.

It is desirable to use B as the p-type doping element in the p-type Si region 503, and the concentration is about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ (that is, particularly p ⁺ -type). By being doped in such a high concentration, a junction having a tunnel junction characteristic or a characteristic equivalent thereto is formed with the n-type Si region 504 that is also highly doped.

  At this time, the doping concentration does not need to be realized over the entire p-type Si region 503, but is at least a region in contact with the n-type Si region 504, specifically, at least one atomic layer or more, a p-type Si region. What is necessary is just to be implement | achieved in the range below the thickness of 503.

  Here, the thickness of the p-type Si region 503 is set to about 50 nm or less, more preferably 20 nm or less, so that light absorption loss and resistance loss in this layer are reduced as much as possible. More preferably, by setting the thickness to 5 nm or less so that carriers can tunnel through the p-type Si region 503 itself, the resistance loss caused by the p-type Si region 503 can be almost zero, and the ohmic characteristics are reduced. Almost no semiconductor / electrode contact can be obtained.

As a manufacturing method of the p-type Si region 503, it can be formed at a temperature of about 800 to 1000 ° C. using a thermal diffusion method using BBr ₃ as a diffusion source, but in order not to impair the bonding characteristics formed before this step, In this step, a hydrogenated amorphous silicon film or a crystalline silicon film containing a microcrystalline Si phase may be formed at a substrate temperature of about 400 ° C. or lower using the thin film technology and conditions described in the first embodiment. preferable. Note that if the n-type Si region 504 is formed by thin film technology, it is necessary to form this process using thin film technology as well.

  FIG. 5 shows the case where the p-type Si region 503 is formed over the entire surface of the n-type Si region 504, but more preferably, the p-type Si region 503 has a minimum formation region immediately below a surface electrode 501 described later. The incident light absorption loss in the p-type Si region 503 is reduced as much as possible (the result of Example 2 described later is obtained under this condition). Patterning can be realized using an appropriate mask or can be formed using an etching method.

  Next, before the back electrode 508 is formed on the above-described p-type Si-BSF region 506, the n-type Si region 507 is formed between the semiconductor / electrode contact structure of the present invention on the back side. Form with interposition. At this time, a tunnel junction or a junction having junction characteristics equivalent to the tunnel junction is formed and manufactured under the conditions described below.

P is preferably used as the n-type doping element in the n-type Si region 507, and the doping concentration is set to about 1 × 10 ^{18 to} 5 × 10 ²¹ / cm ³ (that is, particularly n ⁺ -type). By being doped at such a high concentration, a junction having a tunnel junction characteristic or a property equivalent thereto is formed between the p-type Si-BSF region 506 also doped at a high concentration.

  At this time, the doping concentration does not need to be realized over the entire n-type Si region 507, but is at least a region in contact with the p-type Si-BSF region 506, specifically, at least one atomic layer or more. What is necessary is just to be implement | achieved in the range below the area | region thickness of Si area | region 507.

  Here, the thickness of the n-type Si region 507 is set to about 50 nm or less, more preferably 20 nm or less, so that light absorption loss and resistance loss in this layer are reduced as much as possible. More preferably, by setting the thickness to 5 nm or less, if the carriers can tunnel the n-type Si region 507 itself, the resistance loss caused by the n-type Si region 507 can be almost zero, and the ohmic characteristics are reduced. Almost no semiconductor / electrode contact can be obtained.

The n-type Si region 507 can be formed by using a thermal diffusion method using POCl ₃ as a diffusion source at a temperature of about 700 to 1000 ° C. In order not to impair the bonding characteristics formed before this step, In this step, a hydrogenated amorphous silicon film or a crystalline silicon film (a microcrystalline silicon film or a nanosilicon film) is formed at a substrate temperature of about 400 ° C. or lower by using the thin film technique described in the first embodiment. It is preferable. If the p-type Si-BSF region 506 is formed by a thin film technique, this step needs to be formed using the thin film technique as well.

Next, an antireflection film 502 is formed. As the antireflection film material, Si ₃ N ₄ film, TiO ₂ film, SiO ₂ film, MgO film, ITO film, SnO ₂ film, ZnO film, or the like can be used. The thickness is appropriately selected depending on the material to realize the non-reflection condition for the incident light (if the refractive index of the material is n and the wavelength of the spectral region to be non-reflection is λ, (λ / n) / 4 = d is set. D to satisfy is the optimum film thickness of the antireflection film). For example, in the case of a commonly used Si ₃ N ₄ film (n = about 2), if the non-reflection target wavelength is 600 nm, the film thickness may be about 75 nm.

  As a manufacturing method, a PECVD method, a vapor deposition method, a sputtering method, or the like is used, and the film is formed at a temperature of about 400 to 500 ° C. The antireflection film 502 is patterned in a predetermined pattern in order to form a surface electrode 501 described later. As a patterning method, an etching method (wet or dry) used for a mask such as a resist, or a method in which a mask is formed in advance at the time of forming the antireflection film and then removed after the formation of the antireflection film can be used.

  Next, the front electrode 501 is formed. As the surface electrode material, it is desirable to use a material containing at least one low-resistance metal such as Ag, Cu, or Al. As a production method, a printing method using a paste containing these metals, or a vacuum film formation method such as a sputtering method or a vapor deposition method can be used.

In order to particularly increase the bonding strength between the surface electrode 501 and the Si semiconductor, an oxide component such as TiO ₂ is slightly included in the paste in the printing method, and the interface between the surface electrode 501 and the Si semiconductor in the vacuum film forming method. It is preferable to insert a metal layer mainly composed of Ti. The shape of the surface electrode 501 may be a general comb pattern.

  Next, the back electrode 508 is formed. As the back electrode material, it is desirable to use a metal whose main component is Ag, which has a high reflectivity with respect to Si, but a metal whose main component is Al whose reflectivity for Si is somewhat inferior to that of Ag. However, it can be used effectively unless high efficiency is particularly desired.

As a production method, a printing method using a paste containing these metals, or a vacuum film formation method such as a sputtering method or a vapor deposition method can be used. In order to particularly increase the adhesive strength between the back electrode 508 and the Si semiconductor, an oxide component such as TiO ₂ is slightly included in the paste in the printing method, and the back electrode 508 and the Si semiconductor are formed in the vacuum film forming method. It is preferable to insert a metal layer mainly composed of Ti at the interface. In the latter case, it is desirable that the Ti-based metal layer has a thickness of 5 nm or less and suppresses a reduction in reflectance due to the insertion of the metal layer. The back electrode 508 is preferably formed on the entire back surface of the substrate in order to increase the reflectance of the long wavelength light reaching the back surface.

  Thus, a bulk Si solar cell to which the present invention is applied is realized.

  Note that the order of the above steps is not limited to the above order, and may be any order as long as the temperature of the subsequent process satisfies the condition lower than the temperature of the preceding process.

  In the above description, the solar cell in which the semiconductor / electrode contact structure of the present invention is applied to both the front electrode 501 side and the back electrode 508 side has been described. Of course, the solar cell is applied only to the front electrode side or only to the back electrode side. Needless to say, the effects of the present invention can be obtained even in such a case.

  Next, the solar cell module according to the present invention will be described.

  Usually, since a single solar cell element generates a small electric output, it is generally used as a solar cell module in which a plurality of solar cell elements are electrically connected in series and parallel. Further, by combining a plurality of the solar cell modules, a practical electrical output can be taken out.

  As already described, the solar cell element using the semiconductor / electrode contact structure of the present invention has high conversion efficiency. Therefore, the solar cell module including the solar cell element of the present invention is also highly efficient. Hereinafter, an embodiment of the solar cell module of the present invention will be described with reference to FIG.

  In the following description, the solar cell element 10 of the present invention will be described using an example using the bulk Si solar cell shown in FIG. 5 described in the second embodiment, but is limited to this example. is not.

  As shown in FIG. 9, glass, polycarbonate resin, or the like is used as the translucent panel 12. As the glass, blue plate glass (soda lime glass) white plate glass (borosilicate glass), tempered glass, double tempered glass, heat ray reflective glass, etc. are used, but generally white plate tempered glass having a thickness of about 3 mm to 5 mm is often used. used. In the case of a polycarbonate resin, a resin having a thickness of about 5 mm is often used.

  As the filler 13, a material having translucency, heat resistance, and electrical insulation is preferably used. In addition to an ethylene vinyl acetate copolymer (EVA) having a vinyl acetate content of 20 to 40%, polyvinyl butyral (PVB ) Etc. as a main component, and a sheet-like form having a thickness of about 0.4 to 1 mm is used. In the production of the solar cell module 17, the filler 13 is often arranged on both the front side and the back side of the solar cell element, and these are thermally cross-linked and fused to other members in the laminating step under reduced pressure. And integrate.

  The back surface protective material 14 is made of a weather-resistant fluorine-based resin sheet sandwiching an aluminum foil so as not to transmit moisture, a polyethylene terephthalate (PET) sheet deposited with alumina or silica, or the like.

  The tab 11 is made of, for example, a conductive material whose main component is copper foil and whose surface is coated with solder. This is cut into a predetermined length and used by being soldered to the front electrode 501 and the back electrode 508 for taking out the output of the solar cell element 10.

  Note that solder regions may be formed on the surfaces of the front electrode 501 and the back electrode 508 of the solar cell element 10 on the electrodes by a solder dipping process in which the surfaces are immersed in solder as necessary. In addition, when it is set as the solderless electrode which does not use a solder material, a solder dipping process is abbreviate | omitted.

  To actually wire the tab 11, first, one end of the tab 11 is bonded to the surface electrode 501 of the solar cell element 10 by soldering with hot air or a hot plate. Subsequently, when the other end of the tab 11 is made into a module, it is similarly soldered and adhered to the back electrode 508 on the back side of the adjacent solar cell element 10. In the case of parallel connection, the surface electrodes 501 of adjacent solar cell elements 10 may be bonded together. This is repeated to produce a solar cell element group in which a plurality of solar cell elements 10 are connected.

  In addition, although it will be effective if at least one solar cell element 10 of the present invention is included in the solar cell element group, in order to achieve the effect of the invention satisfactorily, the sun constituting the solar cell element group It is more desirable that all the battery elements are the solar battery element 10 of the present invention.

  The output wiring 15 transmits electrical output from the group of solar cell elements 10 connected by the tab 11 to the terminal of the terminal box 16, and is usually a copper foil having a thickness of about 0.1 mm to 0.5 mm and a width of about 6 mm. The whole surface of which is coated with a solder of about 20 to 70 μm is cut into a predetermined length and soldered to the electrodes of the solar cell element 10.

  Here, the translucent panel 12, the front-side filler 13, the solar cell element group in which the tab 11 and the output wiring 15 are connected to the plurality of solar cell elements 10, the back-side filler 13, and the back surface protective material. 14 laminates are bonded and integrated. That is, after setting the laminated body of each member in a device called a laminator that pressurizes while heating in a reduced pressure state, the pressure is reduced to about 50 to 150 Pa in order to remove the air inside the solar cell module 17, and 100 to 200 ° C. The pressure is applied while heating at a temperature of 15 minutes to 1 hour. As a result, the fillers 13 respectively arranged on the front side and the back side are softened and crosslinked and fused, so that the members can be bonded and integrated to produce the panel portion of the solar cell module 17.

  Furthermore, the terminal box 16 is attached to the back surface of the panel portion of the solar cell module 17 manufactured by the above-described method using an adhesive. The terminal box 16 is used to connect the output wiring 15 from the solar cell element 10 and a cable (not shown) for connecting to an external circuit, and is usually modified with a modified PPE resin in consideration of light resistance against ultraviolet rays and the like. Made in black. Further, the general size of the terminal box 16 is generally about 100 × 60 × 20 mm in a general solar cell module having an output of about 160 W.

  Usually, a module frame (not shown) is often provided for each side of the panel portion of the solar cell module 17. The module frame is often made by extrusion molding of aluminum, and the surface thereof is subjected to anodizing. And this module frame is inserted in each outer periphery side of the panel part of a solar cell, and each corner part is fixed with a bis | screw etc. By providing such a module frame, mechanical strength and weather resistance can be imparted, and the module can be easily handled when a solar cell module is installed.

  The solar cell module of this invention is implement | achieved by the above. Since the solar cell module of the present invention includes the solar cell element of the present invention having the semiconductor / electrode contact structure of the present invention, it has high conversion efficiency.

  It should be noted that the embodiment of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  For example, in the above description, a solar cell using a p-type Si substrate has been described, but even when an n-type Si substrate is used, the effect of the present invention can be achieved by the same process if the polarity in the above description is reversed. Can get. Furthermore, although the case of single junction has been described, even if it is a multi-junction type formed by laminating a thin film junction layer made of a semiconductor multilayer film as described in the first embodiment on a junction element using a bulk substrate, The present invention is applicable.

  As described above, the embodiments of the present invention have been described by taking the thin film Si solar cell and the bulk Si solar cell as examples. However, the present invention is not limited to these, and is optional as long as it does not depart from the principle and purpose of the invention. It can be made the form.

  The present invention is not limited to Si solar cells, but can be applied to compound solar cells and organic solar cells. Furthermore, this invention is applicable also to photoelectric conversion apparatuses other than a solar cell. The present invention is also applicable to general semiconductor elements having a semiconductor / electrode structure other than the photoelectric conversion device, such as a diode, a transistor, and a thyristor.

  Examples of the present invention will be described below. In addition, this invention is not limited only to a following example.

A thin-film Si solar cell element was produced based on the first embodiment of the present invention described with reference to FIG. The conditions are shown in Table 1.

The first electrode 2 that is the front electrode is SnO ₂ , and the second electrode 4 that is the back electrode is a ZnO / Ag laminated structure (the second semiconductor bonding layer 32 side is ZnO). The n-type semiconductor layer 31d and the p-type semiconductor layer 32d according to the semiconductor / electrode contact structure of the present invention were formed by changing the conditions by the Cat-PECVD method. The changed conditions are doping element concentration, thickness, addition of band gap widening element (adjustment of band gap value), presence / absence of Si crystal phase inclusion, and specifically, as described in Table 1.

The p-type semiconductor layer 31a and the n-type semiconductor layer 32a were formed by the Cat-PECVD method, respectively. As shown in Table 1, these semiconductor layers were formed while adjusting the dopant amount so that the doping element concentration was 1 × 10 ¹⁸ cm ⁻³ or more.

Although omitted in the table, for the photoactive layer 31b of the first semiconductor junction layer 31 that is a top cell, an i-type hydrogenated amorphous silicon film is formed to a thickness of 0.3 μm, and As for the n-type semiconductor layer 31c laminated on the substrate, a hydrogenated amorphous silicon film to which P is added as a dopant at a concentration of 3 × 10 ¹⁹ to 1 × 10 ²¹ cm ⁻³ has a thickness of 10 nm, both of which are Cat-PECVD methods. It was produced by.

Further, of the second semiconductor junction layer 32 that is a bottom cell, the p-type semiconductor layer 32 c includes a microcrystalline silicon phase to which B is added as a dopant at a concentration of 1 × 10 ^{19 to} 7 × 10 ²⁰ cm ^−3. As for the photoactive layer 32b stacked on the crystalline silicon film with a thickness of 10 nm, an i-type microcrystalline silicon film was formed with a thickness of 2 μm, and both were prepared by Cat-PECVD method.

  In Table 1, Sample No. Reference numeral 1 denotes a conventional contact structure in which a reverse conductivity type semiconductor layer is not provided at the semiconductor / electrode interface. The others are provided with a semiconductor layer of reverse conductivity type at the semiconductor / electrode interface according to the structure of the present invention. Films 5, 8, 13, and 16 were formed so that the doping element concentration was outside the range of the present invention.

In order to obtain the doping element concentrations shown in Table 1, a sample prepared by changing the addition amount of the dopant gas in advance was measured by SIMS (secondary ion mass spectrometry) to obtain the film forming conditions. It was determined. In SIMS, among the doping elements, O ²⁺ was used as the primary ion source for B, and Cs ⁺ was used as the primary ion source for P. The element concentration was estimated by measuring several different points in the analysis target area and taking the average.

  Regarding the thickness, the film thickness of the film formed on the dummy substrate in advance under each film forming condition is measured with a stylus method step measuring instrument, and the target film thickness is determined using the film forming speed determined from the measured film thickness. It was.

As for the band gap value of the thin film, a so-called tautz plot method is used in which the thin film is formed on a glass substrate and calculated using the light absorption coefficient α calculated from the spectral transmittance data (αhν∝ (hν− Eg) Eg can be obtained by plotting the square root of αhν with respect to hν using the relational expression of ² ; when the right side is set to the third power in the previous equation, the third root of αhν is plotted with respect to hν. To obtain Eg). The values shown in Table 1 are values according to a square root plot.

Furthermore, regarding the presence or absence of Si crystal phase, the case where it is a microcrystalline Si phase having a crystallization rate of 60% or more by Raman spectroscopic evaluation method is included (circle mark in the figure), and the case is less than that Was determined as containing no (× in the figure). The crystallization rate, defined crystalline phase peak intensity in the Raman scattering spectrum / (crystalline phase peak intensity + amorphous phase peak intensity), the crystalline phase peak intensity, a peak intensity at 500~510cm ^-1 + 520cm ^-1 And the amorphous phase peak intensity was defined as the peak intensity at 480 cm ⁻¹ . The Raman spectrum was measured using a Ramanscope System 1000 manufactured by Renishaw using a He—Ne laser (wavelength 632.8 nm) as excitation light.

Table 2 shows the characteristics and evaluation results of the thin-film solar cell elements of the samples shown in Table 1.

  Here, in order to obtain the average characteristics and yield in Table 2, 48 elements were formed on a 10 cm square substrate, and the average characteristics and yield were evaluated. Comprehensive evaluation was conducted using sample no. Based on the conventional structure of No. 1, determination was made by three types: Δ: effective but not so remarkable, ○: good effect obtained, ◎: remarkable effect obtained. .

  From Table 2, the sample No. out of the scope of the present invention. 1, 5, 8, 13, 16 are less than or equal to Δ, but the others are generally better than that, and the structure of the present invention has a great effect on improving device characteristics and yield. Was confirmed.

Based on the first embodiment of the present invention, a bulk type solar cell element was formed as follows. The conditions are shown in Table 3.

A p-type Si substrate (dopant B concentration, 2 × 10 ¹⁶ cm ⁻³ ) having a thickness of 300 μm is used as a p-type Si photoactive region 505, on which an n-type Si region 504 is doped with P by a thermal diffusion method, It produced so that it might become 1 * 10 < ¹⁸ > cm < ^-3 > or more. Further, the p-type Si—BSF region 506 was doped with Al by a paste printing firing method.

  Thereafter, a p-type Si region 503 and an n-type Si region 507 according to the semiconductor / electrode contact structure of the present invention were formed on these regions while changing the conditions by the Cat-PECVD method. The changed conditions are the doping element concentration, thickness, and presence / absence of Si crystal phase inclusion, and are specifically as described in Table 3. In addition, about the p-type Si area | region 503, it formed into a film according to the size of the surface electrode 501 mentioned later with a mask.

  Further, an antireflection film of silicon nitride was formed on these regions with a film thickness of about 75 nm by PECVD, and then the front electrode 501 and the back electrode 508 were both formed by sputtering Ag. The front electrode 501 has a comb pattern, and the back electrode 508 is formed on the entire surface.

  In Table 3, sample no. Reference numeral 1 shows a conventional contact structure in which a semiconductor region having a reverse conductivity is not provided at the semiconductor / electrode interface. All others are provided with a semiconductor region of reverse conductivity at the semiconductor / electrode interface according to the structure of the present invention. 2 is provided only on the surface electrode 501 side. 3 is provided only on the back electrode 508 side. 4 is provided on both the front electrode 501 and the back electrode 508.

  Note that the measurement method and determination method, such as the doping element concentration and thickness, and the presence or absence of the Si crystal phase, were carried out in exactly the same manner as in Example 1.

Table 4 shows the characteristics and evaluation results of the bulk solar cell elements of the samples shown in Table 3.

  Comprehensive evaluation was conducted using sample no. Based on the conventional structure of No. 1, the determination was made in two types: ○: a good effect was obtained, and ◎: a remarkable effect was obtained.

  From Table 4, the sample No. 1, only a yield of 90% or less was obtained. Good results were obtained for 2-4. In particular, sample No. 1 in which both the front electrode 501 and the back electrode 508 are provided with the semiconductor / electrode contact structure of the present invention. No. 4 gave very good results. It was confirmed that the structure of the present invention has a great effect on the improvement of device characteristics and the yield.

It is sectional drawing which shows the structure of the multijunction type thin film Si solar cell element which is one Embodiment of this invention. FIG. 7 is a band diagram of a pin junction type semiconductor device to which the semiconductor / electrode contact structure of the present invention of FIG. 6 is applied. It is a block diagram of the conventional pin junction type solar cell. It is a band figure of the conventional pin junction type semiconductor element. It is a block diagram of the bulk type solar cell element which is one Embodiment of this invention. It is sectional drawing which shows the structure of the pin junction type element to which the contact structure of the semiconductor / electrode of this invention is applied. It is a band figure which shows the state before a contact of the multijunction type thin film Si solar cell of this invention of FIG. It is a band figure which shows the state after a contact of the multi-junction type thin film Si solar cell of this invention of FIG. It is a schematic diagram which shows the structure of the cross section of the solar cell module of this invention.

Explanation of symbols

1: Substrate 2: First electrode 3: Semiconductor multilayer film 3a: p-type semiconductor layer 3b: i-type semiconductor layer 3c: n-type semiconductor layer 31: first semiconductor junction layer 31a: p-type semiconductor layer 31b: photoactive Layer 31c: n-type semiconductor layer 31d: n-type semiconductor layer 32: second semiconductor junction layer 32a: p-type semiconductor layer 32b: photoactive layer 32c: n-type semiconductor layer 32d: p-type semiconductor layer 4: second electrode 501: front electrode 502: antireflection film 503: p-type Si region 504: n-type Si region 505: p-type Si photoactive region 506: p-type Si-BSF region 507: n-type Si region 508: back electrode 6: n Type semiconductor 7: p-type semiconductor 10: solar cell element 11: tab 12: translucent panel 13: filler 14: back surface protective material 15: output wiring 16: terminal box 17: solar cell module

Claims (33)

In a contact portion between a semiconductor having one conductivity type and an electrode, a reverse conductivity semiconductor having a conductivity type opposite to the one conductivity type semiconductor is interposed between the one conductivity type semiconductor and the electrode, and A semiconductor / electrode contact structure in which a doping element concentration in both semiconductors in a region where the conductive semiconductor and the reverse conductive semiconductor are in contact is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less , A semiconductor / electrode contact structure, wherein the thickness of the reverse conductivity type semiconductor is not less than one atomic layer and not more than 5 nm . In the region before Symbol the one conductivity type semiconductor and said opposite conductivity type semiconductor in contact, the doping element concentration of the opposite conductivity type in the semiconductor over a given thickness ^{d1, 1 × 10 18 / cm} 3 or more to 5 × ¹⁰ 21 / cm ³ 2. The semiconductor / electrode contact structure according to claim 1, wherein:   3. The semiconductor / electrode contact structure according to claim 2, wherein the predetermined thickness d1 is not less than one atomic layer and not more than the total thickness of the reverse conductivity type semiconductor. In a region where the one conductivity type semiconductor and the opposite conductivity type semiconductor are in contact with each other, the doping element concentration in the one conductivity type semiconductor is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less over a predetermined thickness d2. 4. The semiconductor / electrode contact structure according to claim 2, wherein the contact structure is a semiconductor / electrode contact structure.   5. The semiconductor / electrode contact structure according to claim 4, wherein the predetermined thickness d2 is not less than one atomic layer and not more than the total thickness of the one conductivity type semiconductor. Contact structure of a semiconductor / electrode according to any one of claims 1 to 5, characterized in that said in opposite conductivity type semiconductor contains elements to enlarge the band gap of the semiconductor. 7. The semiconductor / electrode contact structure according to claim 6 , wherein the element that expands the band gap includes at least one element selected from the group consisting of carbon, oxygen, and nitrogen. Contact structure of a semiconductor / electrode according to any one of claims 1 to 7, characterized in that said in opposite conductivity type semiconductor contains areas to reduce light absorption coefficient of the semiconductor. 9. The semiconductor / electrode contact structure according to claim 8 , wherein the region for reducing the absorption coefficient is a crystal-containing phase. The semiconductor / electrode contact structure according to any one of claims 1 to 9 , wherein the electrode is made of a transparent conductive material. In a contact portion between a semiconductor having one conductivity type and an electrode, a reverse conductivity semiconductor having a conductivity type opposite to the one conductivity type semiconductor is interposed between the one conductivity type semiconductor and the electrode, and A semiconductor / electrode contact structure in which a doping element concentration in both semiconductors in a region where the conductive semiconductor and the reverse conductive semiconductor are in contact is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less, contact structure of the electrode you characterized in that it consists of metallic material semiconductors / electrodes. In the region before Symbol the one conductivity type semiconductor and said opposite conductivity type semiconductor in contact, the doping element concentration of the opposite conductivity type in the semiconductor over a given thickness ^{d1, 1 × 10 18 / cm} 3 or more to 5 × ¹⁰ 21 / cm ³ 12. The semiconductor / electrode contact structure according to claim 11, wherein: 13. The semiconductor / electrode contact structure according to claim 12 , wherein the predetermined thickness d1 is not less than one atomic layer and not more than the total thickness of the reverse conductivity type semiconductor. In a region where the one conductivity type semiconductor and the opposite conductivity type semiconductor are in contact with each other, the doping element concentration in the one conductivity type semiconductor is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less over a predetermined thickness d2. contact structure of a semiconductor / electrode according to claim 12 or claim 13, characterized in that the. 15. The semiconductor / electrode contact structure according to claim 14 , wherein the predetermined thickness d2 is not less than one atomic layer and not more than the total thickness of the one conductivity type semiconductor. 16. The semiconductor / electrode contact structure according to claim 11, wherein the thickness of the reverse conductivity type semiconductor is not less than one atomic layer and not more than 5 nm. Contact structure of a semiconductor / electrode according to any one of claims 11 to 16, characterized in that said in opposite conductivity type semiconductor contains elements to enlarge the band gap of the semiconductor. 18. The semiconductor / electrode contact structure according to claim 17 , wherein the element that expands the band gap includes at least one element selected from the group consisting of carbon, oxygen, and nitrogen. Contact structure of a semiconductor / electrode according to any one of claims 11 to 18, characterized in that it contains areas to reduce light absorption coefficient of the semiconductor in the opposite conductivity type semiconductor. 20. The semiconductor / electrode contact structure according to claim 19 , wherein the region for reducing the absorption coefficient is a crystal-containing phase. In the contact portion between the semiconductor having one conductivity type and the electrode, the one conductivity type semiconductor and the electrode are provided.
A doping element concentration in both semiconductors in a region where the one-conductivity-type semiconductor and the opposite-conductivity-type semiconductor are in contact with each other, with a reverse-conductivity-type semiconductor having a conductivity type opposite to that of the one-conductivity-type semiconductor interposed therebetween 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less of a semiconductor / electrode contact structure, wherein the electrode has a two-layer structure of a transparent conductive material layer and a metal material layer, the transparent conductive material layer, the semi-conductor / contact of the electrode structure you characterized by being located on the contact surface side of the semiconductor. In the region before Symbol the one conductivity type semiconductor and said opposite conductivity type semiconductor in contact, the doping element concentration of the opposite conductivity type in the semiconductor over a given thickness ^{d1, 1 × 10 18 / cm} 3 or more to 5 × ¹⁰ 21 / cm ³ The semiconductor / electrode contact structure according to claim 21, wherein 23. The semiconductor / electrode contact structure according to claim 22 , wherein the predetermined thickness d1 is not less than one atomic layer and not more than the total thickness of the reverse conductivity type semiconductor. In a region where the one conductivity type semiconductor and the opposite conductivity type semiconductor are in contact with each other, the doping element concentration in the one conductivity type semiconductor is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less over a predetermined thickness d2. 24. The semiconductor / electrode contact structure according to claim 22 or 23 . 25. The semiconductor / electrode contact structure according to claim 24 , wherein the predetermined thickness d2 is not less than one atomic layer and not more than the total thickness of the one conductivity type semiconductor. The semiconductor / electrode contact structure according to any one of claims 21 to 25 , wherein the thickness of the reverse conductivity type semiconductor is not less than one atomic layer and not more than 5 nm. Contact structure of a semiconductor / electrode according to any one of claims 2 1 to claim 26, characterized in that it contains the elements to enlarge the band gap of the semiconductor in said opposite conductivity type semiconductor. 28. The semiconductor / electrode contact structure according to claim 27 , wherein the element that widens the band gap includes at least one element selected from the group consisting of carbon, oxygen, and nitrogen. Contact structure of a semiconductor / electrode according to any one of claims 21 to claim 28, characterized in that it contains areas to reduce light absorption coefficient of the semiconductor in the opposite conductivity type semiconductor. 30. The semiconductor / electrode contact structure according to claim 29 , wherein the region where the absorption coefficient is reduced is a crystal-containing phase. The semiconductor / electrode contact structure according to any one of claims 1 to 30 , wherein at least one of the semiconductor / electrode contact portions is a semiconductor element having a plurality of semiconductor / electrode contact portions. A semiconductor element characterized by the above. 32. A solar cell element comprising the semiconductor element according to claim 31 . A solar cell module having a plurality of solar cell elements arranged in an electrically connected manner, wherein the plurality of solar cell elements includes the solar cell element according to claim 32. Solar cell module.

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