JP2006093477A - Zinc oxide layer and photovoltaic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively form a zinc oxide layer with excellent reflection characteristics/electric characteristics, and to inexpensively supply a highly efficient element by incorporating the layer in a photovoltaic element. <P>SOLUTION: The photovoltaic element formed by stacking at least the zinc oxide layer and a semiconductor layer on a substrate, wherein the zinc oxide layer contains chlorine atoms of 1.0×10<SP>18</SP>cm<SP>-3</SP>≤ and ≥5.0×10<SP>19</SP>cm<SP>-3</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zinc oxide layer and a photovoltaic element formed by stacking a zinc oxide layer and a semiconductor layer.

  Conventionally, photovoltaic devices made of hydrogenated amorphous silicon, hydrogenated amorphous silicon germanium, hydrogenated amorphous silicon carbide, microcrystalline silicon, polycrystalline silicon, etc., improve collection efficiency at long wavelengths. In addition, the back reflective layer has been used. Such a reflective layer desirably exhibits an effective reflective characteristic at a wavelength close to the band edge of the semiconductor material and at which absorption is reduced, that is, from 800 nm to 1200 nm. It is metals such as gold, silver, copper, and aluminum and their alloys that sufficiently satisfy this condition. An optically transparent uneven layer is also provided in a predetermined wavelength range known as optical confinement. Generally, an uneven transparent conductive layer is provided between the metal layer and the semiconductor active layer. Thus, attempts have been made to improve the short-circuit current density Jsc by effectively using the reflected light. Further, the transparent conductive layer prevents deterioration of characteristics due to a shunt path. Very generally, these layers are deposited by methods such as vacuum evaporation and sputtering, and show improved short circuit current density.

  As an example, Non-Patent Document 1, Non-Patent Document 2, and the like have examined the reflectance and texture structure of a reflective layer composed of silver atoms. In these examples, an effective unevenness is formed by depositing the reflective layer with two layers of silver formed by changing the substrate temperature, and in this way, in combination with the zinc oxide layer, the short circuit current due to the light confinement effect is reduced. The increase is said to have been achieved.

  Moreover, in patent document 1, the electrolyte solution for zinc oxide layer preparation which consists of aqueous solution containing zinc ion 0.001 mol / l-0.5 mol / l and nitrate ion 0.001 mol / l-0.5 mol / l is used. It is disclosed that the zinc oxide layer produced in this manner has a uniform film thickness and composition and a zinc oxide layer excellent in optical transparency.

  In Patent Document 2, a step of forming a first zinc oxide thin film on a substrate by a sputtering method, and immersing the substrate in an aqueous solution containing at least nitrate ions, zinc ions, and carbohydrates, A method of forming a second zinc oxide thin film on the first zinc oxide thin film by energizing the electrode immersed in the electrode, and a method for producing the zinc oxide thin film, which is inexpensive It is disclosed that it is possible to suppress the abnormal growth of the film and to form a zinc oxide thin film having excellent substrate adhesion.

  Further, in Patent Document 3, a conductive substrate and a counter electrode are immersed in an aqueous solution containing at least nitrate ions and zinc ions, and a current is passed between the conductive substrate and the counter electrode, whereby the conductive substrate and the counter electrode are placed on the conductive substrate. In the method of forming a zinc oxide layer in which a zinc oxide layer is formed, an oxidation solution formed using an aqueous solution containing a polyvalent carboxylic acid in which carboxyl groups are bonded to a plurality of carbons having sp2 hybrid orbitals or an ester thereof as the aqueous solution. It is disclosed that the zinc layer has a texture shape with a high light confinement effect.

Japanese Patent No. 3273294 Japanese Patent Laid-Open No. 10-140373 JP 2002-167695 A "Optical confinement effect in a-SiGe solar cell on 29p-MF-22 stainless steel substrate" (Autumn 1990) Proceedings of the 51st JSAP scientific conference p747 P-IA-15a-SiC / a-Si / a-SiGe Multi-Bandgap Stacked Solar Cells With Bandgap Profiling, “Sanomiya et al., Technical Digest of the International Jp 19

  As described above, the light confinement layer already disclosed has excellent light conversion characteristics. However, in Non-Patent Document 1 and Non-Patent Document 2, the zinc oxide layer is heated by resistance heating or vacuum deposition using an electron beam, It is formed only by the sputtering method, ion plating method, CVD method, etc., and the production cost of the target material etc. is high, the depreciation cost of the vacuum equipment is large, and the utilization efficiency of the material is not high This is a great barrier to industrial application of solar cells by making the cost of photovoltaic devices using these technologies extremely high.

  Patent Document 1 discloses a technique relating to the production of a zinc oxide layer having a uniform film thickness and composition and excellent optical characteristics, but does not mention the production of a zinc oxide layer having a texture structure. For example, in a photovoltaic element formed by laminating a semiconductor film on a substrate having a zinc oxide layer on the surface, when a uniform thickness is used as the zinc oxide layer, the light confinement effect Is not sufficiently exhibited, and the photoelectric conversion characteristics, particularly the effect of increasing the short-circuit current is insufficient.

  In addition, the zinc oxide thin film formed by electrodeposition from an aqueous solution containing zinc ions and nitrate ions, particularly when formed under conditions that increase the current density or increase the concentration of the solution, Abnormal growth in the shape of needles, spheres, or resins that exceed the micron order is likely to occur on the deposit, and these anomalies are likely to occur when this zinc oxide thin film is used as part of a photovoltaic device. It is considered that the growth causes a shunt path of the photovoltaic device. Furthermore, the zinc oxide thin film formed by electrodeposition from an aqueous solution containing zinc ions and nitrate ions tends to vary in the size of zinc oxide crystal grains, and has a problem in uniformity when the area is increased. It was. Further, the zinc oxide thin film formed by electrodeposition from an aqueous solution containing zinc ions and nitrate ions has an adhesion property to the substrate, such as resistance heating or electron beam vacuum deposition, sputtering, ion plating. There is a problem that it is inferior to those formed by the method, the CVD method or the like.

  The techniques disclosed in Patent Document 2 and Patent Document 3 have a shape excellent in light confinement effect, reduce abnormal growth, and improve uniformity, and are excellent as a substrate of a photovoltaic device. In order to obtain a higher photovoltaic element characteristic, the zinc oxide layer has a transmittance and conductivity more suitable for the photovoltaic element while maintaining the shape rich in irregularities. Is important.

  The present invention has been made in view of such circumstances, and a zinc oxide layer having further excellent reflection characteristics and electrical characteristics compared to conventional methods can be formed at low cost, and this can be used as a photovoltaic device. By incorporating it, an object is to supply a highly efficient device at a low cost.

  The configuration of the present invention made to achieve the above object is as follows.

That is, the present invention is a zinc oxide layer formed on a substrate, the zinc oxide layer containing 1.0 × 10 ¹⁸ cm ⁻³ or more and 5.0 × 10 ¹⁹ cm ⁻³ or less chlorine atoms. It is in the zinc oxide layer characterized by having.

The present invention also relates to a photovoltaic element formed by laminating at least a zinc oxide layer and a semiconductor layer on a substrate, the zinc oxide layer being 1.0 × 10 ¹⁸ cm ⁻³ or more and 5.0 × The photovoltaic element is characterized by containing chlorine atoms of 10 ¹⁹ cm ⁻³ or less.

  In the photovoltaic device of the present invention, it is preferable that the chlorine atom in the zinc oxide layer has a maximum content in the film, with the content changing in the thickness direction of the zinc oxide layer. In this case, it is preferable to have a plurality of the maximum values in the zinc oxide layer, and among the plurality of maximum values in the zinc oxide layer, a maximum value existing on the substrate side exists on the semiconductor layer side. It is preferably smaller than the local maximum value.

  Moreover, it is preferable that the maximum value of the content of chlorine atoms contained in the semiconductor layer is smaller than the maximum value of the content of chlorine atoms contained in the zinc oxide layer. In this case, it is preferable that the maximum value of the content of chlorine atoms contained in the semiconductor layer is 1/10 or less of the maximum value of the content of chlorine atoms contained in the zinc oxide layer.

  According to the zinc oxide layer of the present invention, it is possible to form a zinc oxide layer having high transmittance / conductivity while maintaining the configuration of the zinc oxide layer rich in irregularities, and to this, the semiconductor layer The photovoltaic element of the present invention formed by laminating the layers has excellent short circuit current density, low series resistance, and excellent characteristics as a photoelectric conversion element.

As a result of intensive studies in order to solve the above-described problems, the present inventor has found that the zinc oxide layer formed on the substrate has a thickness of 1.0 × 10 ¹⁸ cm ⁻³ or more and 5.0 × 10 ¹⁹ cm ⁻³ or less. By containing chlorine atoms, it is possible to achieve high transmittance and electrical conductivity while maintaining a rich structure of the zinc oxide layer, and by laminating a semiconductor layer on it. The obtained photovoltaic element has been found to have excellent characteristics as a photoelectric conversion element having a large short-circuit current density and a small series resistance.

  In the following, the effect of the characteristics of the present invention will be described.

  As a method for changing the conductivity of the zinc oxide layer, a method in which a metal such as aluminum or lithium is mixed is known. However, this method affects the crystal structure of the entire film, and is rich in uneven shape. The conductivity cannot be changed while maintaining the configuration. On the other hand, according to the method of adding a predetermined amount of chlorine atoms to the zinc oxide layer according to the present invention, it is possible to change the conductivity of the zinc oxide layer while maintaining a configuration rich in uneven shape. Although the detailed mechanism is unknown, the zinc oxide layer according to the present invention does not replace the zinc atom, which is the lattice skeleton, with other metal atoms, so that the influence on the crystal structure of the entire film is minimized. It is presumed that the conductivity can be changed. Also, the chlorine atoms in the zinc oxide layer have the effect of suppressing the generation of strain in the film, and it is thought that there is also the effect of obtaining high transmittance and conductivity by suppressing the strain. Yes.

The amount of chlorine atoms in the zinc oxide layer, 1.0 × 10 ¹⁸ cm ^-3 or more 5.0 × 10 ¹⁹ cm ^-3 or less can be cited as a preferable range. When the amount is less than 1.0 × 10 ¹⁸ cm ⁻³ , the above effect is not significantly exhibited. When the amount is more than 5.0 × 10 ¹⁹ cm ⁻³ , chlorine atoms accumulate at the grain boundaries of the zinc oxide layer. For the reasons described above, the transmittance is rather decreased, which is not preferable.

  The distribution of chlorine atoms in the zinc oxide layer may be configured so that the same amount is uniformly distributed in the film, but the distribution is such that the amount of chlorine atoms is reduced near the interface between the zinc oxide and the adjacent layer. A configuration having a maximum value inside is preferable. According to such a configuration, diffusion of chlorine atoms to the adjacent layer can be effectively prevented. In addition, by relatively reducing the content of chlorine atoms in the initial region of zinc oxide formation, it is possible to suppress the generation of fine crystal grains in the initial region of zinc oxide formation and to form a zinc oxide layer with higher transmittance. The present inventors are thinking.

  In order to make the zinc oxide layer formed on the substrate into a structure with excellent reflection characteristics, the surface shape is controlled so as to be an uneven structure of an appropriate size, and the light in the wavelength range to be reflected is sufficiently A shape that can be reflected is preferable. Specifically, it is preferable to have an uneven shape in the order of the wavelength range to be reflected. As a method for forming a zinc oxide layer when control of the surface shape is required, it is preferable to use an electrodeposition method based on an electrochemical reaction from an aqueous solution at least partly. In the electrodeposition method, by controlling the concentration of ions in the aqueous solution, the type and amount of additives, the aqueous solution temperature, pH, the aqueous solution circulation method, etc., the shape can be controlled more than in other methods such as sputtering. It is possible to carry out simply. In particular, it is preferable to form the surface layer of the zinc oxide layer by an electrodeposition method. In addition, expensive oxide targets and vacuum devices, which are necessary for sputtering, are not necessary for electrodeposition, and materials and manufacturing equipment can be produced at low cost. Forming by an electrodeposition method is advantageous from the viewpoint of cost.

  As described above, as a method for forming a zinc oxide layer satisfying the shape of the present invention, at least a part of the zinc oxide layer is formed by using an electrodeposition method based on an electrochemical reaction from an aqueous solution. Compared with the case where it is carried out in (1), it is preferable because the shape can be controlled without taking measures such as processing after the formation. In particular, the formation of the surface layer of the zinc oxide layer is performed by an electrodeposition method. That is preferred.

  Depending on the combination of the zinc oxide layer and the lower layer, it may be necessary to further strengthen the adhesion between the zinc oxide layer and the lower layer, or the formation of zinc oxide growth nuclei on the lower layer by electrodeposition In the case where it is difficult to form a zinc oxide layer by direct electrodeposition on the lower layer, such as when it is difficult, the zinc oxide layer is first formed by sputtering the first zinc oxide layer, It is preferable to form a layer structure in which the second zinc oxide layer is laminated on the first zinc oxide layer by an electrodeposition method using an electrochemical reaction from an aqueous solution. In this case, it is possible to form zinc oxide layers having various surface shapes by adjusting the conditions of the second zinc oxide layer according to the material and shape of the first zinc oxide layer.

  When the zinc oxide layer has a plurality of laminated structures as described above, the content of chlorine atoms contained in the zinc oxide layer is preferably controlled so as to be a value suitable for each zinc oxide layer. It is a configuration. Similarly, it is also preferable that the chlorine content of each zinc oxide layer has a maximum value inside the film thickness as described above. In this case, the entire zinc oxide layer has a configuration having a plurality of maximum values of chlorine content.

  First, the first zinc oxide layer is formed by sputtering, and the second zinc oxide layer is laminated on the first zinc oxide layer by an electrodeposition method using an electrochemical reaction from an aqueous solution. When it is set as the layer structure to perform, the one where the maximum value of content of the chlorine atom of a 1st zinc oxide layer is smaller than the maximum value of a 2nd zinc oxide layer is a more preferable structure. The reason is that zinc oxide formed by the electrodeposition method has a lower electrical conductivity because the ratio of zinc atoms to oxygen atoms is closer to the stoichiometric ratio than zinc oxide formed by the sputtering method. Inclusion of more chlorine atoms in the formed zinc oxide layer can be a means to increase the conductivity of the zinc oxide layer, or the presence of chlorine atoms can accommodate excess zinc atoms at interstitial positions. It is presumed that the effect of increasing the conductivity of the zinc oxide layer formed by the electrodeposition method is exhibited due to the fact that it has an action.

  Further, when a photovoltaic element is formed by laminating at least the above-described zinc oxide layer and a semiconductor layer on a substrate, in the semiconductor layer containing silicon atoms laminated on the zinc oxide layer, chlorine contained in the semiconductor layer In order for atoms to induce defects and the like, the content is preferably below a predetermined amount, and the amount of chlorine atoms contained in the semiconductor layer is relatively greater than the amount of chlorine atoms contained in the zinc oxide layer. The smaller one is preferable. Specifically, it is preferable that the maximum value of the chlorine atom content contained in the semiconductor layer is 1/10 or less of the maximum value of the chlorine atom content contained in the zinc oxide layer. It is done.

  Next, components of the photovoltaic element of the present invention will be described.

  1 and 2 are schematic cross-sectional views showing examples of the photovoltaic element and the substrate of the present invention. In the figure, 101 is a substrate, 102-1 is an n-type semiconductor layer, 102-2 is an i-type semiconductor layer, 102-3 is a p-type semiconductor layer, 103 is a transparent conductive layer, and 104 is a collecting electrode. Reference numeral 101-1 denotes a base body, 101-2 denotes a reflective layer, and 101-3 denotes a zinc oxide layer. These are constituent members of the substrate 101. Here, the substrate 101 shown in FIG. 2A has a single layer structure of the zinc oxide layer 101-3, and the substrate 101 shown in FIG. Those of the zinc oxide layer 101-3A and the second zinc oxide layer 101-3B). The reflective layer 101-2 is formed as necessary.

(Substrate)
As the substrate 101-1, a plate-like member or sheet-like member made of metal, resin, glass, ceramics, semiconductor bulk, or the like is preferably used. The surface may have fine irregularities. It is good also as a structure which light injects from the base | substrate side using a transparent base | substrate. In the case where light is incident from the transparent substrate side, when the reflective layer 101-2 is provided, the reflective layer 101-2 is disposed on the opposite side of the light incident side from the semiconductor layer. Moreover, continuous film formation using a roll-to-roll method can be performed by making the base into a long shape. In particular, a flexible material such as stainless steel or polyimide is suitable as the material of the base 101-1.

(Reflective layer)
The reflective layer 101-2 has a role as an electrode and a role as a reflective layer that reflects the reached light and reuses it in the semiconductor layer 102. As the material, Al, Cu, Ag, Au, CuMg, AlSi and alloys thereof can be preferably used. It is also preferable that the reflective layer has a laminated structure in which a transition metal such as Ni, Cr, or Ti is used as an underlayer. With such a laminated structure, an effect of further improving the adhesion between the substrate and the reflective layer can be expected. As a method for forming the reflective layer, methods such as vapor deposition, sputtering, electrodeposition, and printing are suitable. The reflective layer 101-2 preferably has an uneven surface. Thereby, the optical path length of the reflected light in the semiconductor layer 102 can be extended, and the short circuit current can be increased.

(Zinc oxide layer)
The zinc oxide layer 101-3 has a role of increasing the irregular reflection of incident light and reflected light and extending the optical path length in the semiconductor layer 102. In addition, the element of the reflective layer 101-2 has a role of preventing the photovoltaic element from being shunted due to diffusion or migration to the semiconductor layer 102. Furthermore, it has a role of preventing a short circuit due to a defect such as a pinhole in the semiconductor layer by having an appropriate resistance. The zinc oxide layer 101-3 preferably has a concavo-convex shape on the order of wavelengths in order to increase the irregular reflection of incident light and reflected light. In order to form the concavo-convex shape described above, at least a part of the zinc oxide layer is formed by an electrodeposition method using an electrochemical reaction from an aqueous solution. It is preferable because it is possible without taking. Further, in order to obtain a zinc oxide layer having optimal transmittance and conductivity while maintaining a shape rich in irregularities, the zinc oxide layer is 1.0 × 10 ¹⁸ cm ⁻³ or more. It preferably contains not more than 5.0 × 10 ¹⁹ cm ⁻³ of chlorine atoms.

As a condition for forming the zinc oxide layer by the electrodeposition method, it is preferable to use an aqueous solution containing nitrate ions and zinc ions in a corrosion-resistant container. The concentration of the substance contained in the aqueous solution varies depending on the shape and material of the underlayer, but the concentration of nitrate ions and zinc ions is preferably in the range of 0.002 mol / l to 2.0 mol / l. It is more desirably in the range of 0.01 mol / l to 1.0 mol / l, and further desirably in the range of 0.1 mol / l to 0.5 mol / l. The source of nitrate ions and zinc ions is not particularly limited, and may be zinc nitrate which is a source of both ions, water-soluble nitrate such as ammonium nitrate which is the source of nitrate ions, and zinc ions. It may be a mixture of zinc salts such as zinc sulfate as a supply source. It is also preferable to add carbohydrates such as saccharose and dextrin to the aqueous solution in order to suppress abnormal growth or improve adhesion. However, excessive carbohydrates are not preferable because the action of specifying the c-axis orientation of zinc oxide is strengthened and the surface shape is flattened. From the above, although the amount of carbohydrate in the aqueous solution depends on the kind of carbohydrate, in the case of sucrose, it is generally 1 g / l to 500 g / l, more preferably 3 g / l to 100 g / l. In the case of dextrin, a preferable range is 0.01 g / l to 10 g / l, more preferably 0.025 g / l to 1 g / l. Further, although the detailed effect and the mechanism thereof are unknown, a plurality of sp2 hybrid orbitals are provided in the aqueous solution for the purpose of controlling the size of the concavo-convex shape of the component or controlling the inclination angle. It is preferable to introduce a polyvalent carboxylic acid having a carboxyl group bonded to carbon or an ester thereof. Examples of the polyvalent carboxylic acid or ester thereof in which a carboxyl group is bonded to a plurality of carbons having sp2 hybrid orbitals include those having a —C═C— group and a carboxyl group or an ester group bonded to each of these carbons, The thing which the carboxyl group couple | bonded with several carbon in a ring (a benzene ring, a heteroaromatic ring, etc.) is mentioned. More specifically, phthalic acid, isophthalic acid, maleic acid, naphthalic acid or esters thereof can be mentioned. However, excess polyvalent carboxylic acid is not preferable because it has a function of miniaturizing the uneven shape of the zinc oxide layer. From the above, the concentration of these polyvalent carboxylic acids is preferably 0.5 μmol / l to 500 μmol / l, and more preferably 1 μmol / l to 300 μmol / l. When depositing a zinc oxide layer by an electrodeposition method, it is preferable to use the substrate on which the zinc oxide layer is deposited in the aqueous solution as a cathode and zinc, platinum, carbon or the like as an anode. The range of the current value flowing between the anode and the cathode is preferably 0.1 mA / cm ^{2 to} 100 mA / cm ² , more preferably 1 mA / cm ^{2 to} 30 mA / cm ² , optimally 4 mA / cm ^{2 to} 20 mA. / Cm ² . The method for incorporating the chlorine atom in the zinc oxide, or used as obtained by mixing the chloride of a predetermined concentration in the raw material, in an aqueous solution Cl, such as zinc sulfate ^- containing chlorine atoms, such as ^- and ClO Examples include a method of mixing ions.

The conditions for forming the zinc oxide layer by the sputtering method are greatly affected by the method, gas type and flow rate, internal pressure, input power, film formation rate, substrate temperature, and the like. For example, in the case of forming a zinc oxide layer using a zinc oxide target by DC magnetron sputtering, examples of the gas include Ar, Ne, Kr, Xe, Hg, O _2, etc., and the flow rate is For example, when the volume of the film formation space is 20 liters, it is preferably 1 cm ³ / min (normal) to 100 cm ³ / min (normal), depending on the size and the exhaust speed. The internal pressure during film formation is preferably 10 mPa to 10 Pa. The input power is preferably 10 W to 10 kW, although it depends on the size of the target. The substrate temperature is preferably in the range of 70 ° C. to 450 ° C., although the preferred range varies depending on the deposition rate. Examples of the method for containing chlorine atoms in zinc oxide include a method in which a gas containing chlorine atoms is mixed in the sputtering gas atmosphere, and a method in which chloride is placed on or mixed in the target material.

(substrate)
After the reflective layer 101-2 is formed on the base 101-1 as necessary by the above method, the substrate 101 is formed by laminating the zinc oxide layer 101-3. Further, an insulating layer may be provided over the substrate 101 in order to facilitate integration of elements.

(Semiconductor layer)
As a main material when a silicon-based thin film is used for the semiconductor layer, an amorphous phase or a crystalline phase, or a mixed phase system thereof is used. Instead of Si, an alloy of Si and C or Ge may be used. The semiconductor layer simultaneously contains hydrogen and / or halogen atoms. Its preferable content is 0.1 to 40 atomic%. Furthermore, the semiconductor layer may contain oxygen, nitrogen, and the like. To make the semiconductor layer a p-type semiconductor layer, a group III element is contained. To make the semiconductor layer an n-type semiconductor layer, a group V element is contained. As the electrical characteristics of the p-type layer and the n-type layer, those having an activation energy of 0.2 eV or less are preferable, and those having an activation energy of 0.1 eV or less are optimal. The specific resistance is preferably 100 Ωcm or less, and most preferably 1 Ωcm or less.

  In the case of a stack cell (photovoltaic element having a plurality of pin junctions), the pin junction i-type semiconductor layer close to the light incident side has a wide band gap, and the band gap narrows as the pin junction becomes far from the light incident side. Preferably it is. In addition, it is preferable that the band gap has a minimum value closer to the p layer than the center in the film thickness direction inside the i layer. The doped layer (p-type layer or n-type layer) on the light incident side is preferably a crystalline semiconductor with little light absorption or a semiconductor with a wide band gap. As an example of a stack cell in which two pairs of pin junctions are stacked, as a combination of i-type silicon semiconductor layers, from the light incident side (amorphous semiconductor layer, semiconductor layer including crystal phase), (semiconductor layer including crystal phase, crystal Semiconductor layer including a phase) and (amorphous semiconductor layer, amorphous semiconductor layer). In addition, as an example of a photovoltaic element in which three sets of pin junctions are stacked, as a combination of i-type silicon-based semiconductor layers, from the light incident side (amorphous semiconductor layer, amorphous semiconductor layer, semiconductor layer including a crystal phase), ( And an amorphous semiconductor layer, a semiconductor layer including a crystal phase, a semiconductor layer including a crystal phase), and a semiconductor layer including a crystal phase, a semiconductor layer including a crystal phase, and a semiconductor layer including a crystal phase.

As an i-type semiconductor layer, the absorption coefficient (α) of light (630 nm) is 5000 cm ⁻¹ or more, and the photoconductivity (σp) of simulated sunlight irradiation by a solar simulator (AM1.5, 100 mW / cm ² ) is 10 ×. It is preferable that 10 ⁻⁵ S / cm or more, dark conductivity (σd) is 10 × 10 ⁻⁶ S / cm or less, and Urbach energy by a constant photocurrent method (CPM) is 55 meV or less. As the i-type semiconductor layer, even a slightly p-type or n-type layer can be used.

(Method for forming semiconductor layer)
In order to form a silicon-based semiconductor and the above-described semiconductor layer, a high-frequency plasma CVD method is suitable. Hereinafter, a preferred example of the procedure for forming the semiconductor layer by the high-frequency plasma CVD method will be shown.

The inside of the deposition chamber (vacuum chamber) that can be decompressed is decompressed to a predetermined deposition pressure. A material gas such as a source gas or a dilution gas is introduced into the deposition chamber, and the deposition chamber is set to a predetermined deposition pressure while the deposition chamber is evacuated by a vacuum pump. The substrate 101 is set to a predetermined temperature by a heater. A high frequency generated by a high frequency power supply is introduced into the deposition chamber. The method of introducing a high frequency into the deposition chamber is a method in which a high frequency is guided through a waveguide and introduced into a deposition chamber through a dielectric window such as alumina ceramics, or a high frequency is guided through a coaxial cable and deposited through a metal electrode. There is a method to introduce it indoors. Plasma is generated in the deposition chamber to decompose the source gas, and a deposited film is formed on the substrate 101 disposed in the deposition chamber. This procedure is repeated a plurality of times as necessary to form the semiconductor layer 102. As conditions for forming the semiconductor layer, the substrate temperature in the deposition chamber is 100 to 450 ° C., the pressure is 50 mPa to 1500 Pa, and the high frequency power is 0.001 to 1 W / cm ³ .

Examples of the source gas suitable for forming the silicon-based semiconductor of the present invention and the semiconductor layer described above include gasifiable compounds containing silicon atoms such as SiH ₄ , Si ₂ H ₆ , and SiF ₄ . In the case of using an alloy system, it is desirable to add a gasifiable compound containing Ge or C such as GeH ₄ or CH ₄ to the raw material gas. The source gas is desirably diluted with a diluent gas and introduced into the deposition chamber. Examples of the dilution gas include H ₂ and He. Further, a gasifiable compound containing nitrogen, oxygen or the like may be added as a source gas or a dilution gas. B ₂ H ₆ , BF ₃ or the like is used as a dopant gas for making the semiconductor layer a p-type layer. Further, PH ₃ , PF ₃ or the like is used as a dopant gas for making the semiconductor layer an n-type layer. In the case of depositing a crystal phase thin film or a layer having a small optical absorption such as SiC or a wide band gap, it is preferable to increase the ratio of the dilution gas to the source gas and introduce a relatively high power high frequency.

(Transparent conductive layer)
The transparent conductive layer 103 is an electrode on the light incident side, and can also serve as an antireflection film by setting its film thickness appropriately. The transparent conductive layer 103 is required to have a high transmittance in the wavelength region that can be absorbed by the semiconductor layer 102 and to have a low resistivity. The transmittance at 550 nm is preferably 80% or more, and more preferably 85% or more. As a material of the transparent conductive layer 103, ITO, ZnO, In ₂ O ₃ or the like can be suitably used. As the formation method, methods such as vapor deposition, CVD, spraying, spin-on, and immersion are suitable. You may add the substance which changes electrical conductivity to these materials.

(Collector electrode)
The collecting electrode 104 is provided on the transparent conductive layer 103 in order to improve the collecting efficiency. As the formation method, a method of forming a metal of an electrode pattern by sputtering using a mask, a method of printing a conductive paste or a solder paste, a method of fixing a metal wire with a conductive paste, and the like are suitable.

  In addition, a protective layer may be formed on both surfaces of the photovoltaic element as necessary. At the same time, a reinforcing material such as a steel plate may be used in combination on the back surface (light incident side and reflection side) of the photovoltaic element.

  In the following examples, the present invention will be specifically described by taking solar cells as examples of photovoltaic elements, but these examples do not limit the contents of the present invention.

Example 1
First, a strip-shaped substrate 101-1 (width 40 cm, length 200 m, thickness 0.125 mm) made of stainless steel (SUS430-BA) is sufficiently degreased and washed, and using the deposited film forming apparatus 301 of FIG. A reflective layer 101-2 and a zinc oxide layer 101-3 made of Ag were formed over the base 101-1, and a substrate 101 having a configuration as shown in FIG. 2A was formed.

  FIG. 3 is a schematic cross-sectional view showing an example of a deposited film forming apparatus for producing a substrate including a zinc oxide layer according to the present invention. The deposited film forming apparatus 301 shown in FIG. 3 is configured by combining a substrate delivery container 302, vacuum containers 311 to 314, and a substrate winding container 303 through a gas gate. In the deposited film forming apparatus 301, a belt-like substrate 101-1 is set through each vacuum container for forming a deposited film. The band-shaped substrate is unwound from a bobbin installed in the substrate delivery container 302 and is wound on another bobbin by the substrate take-up container 303.

  In each vacuum vessel, a target is installed as cathode electrodes 341 to 344, and by applying a direct current power source 351 to 354 to the cathode electrode, a reflective layer 101-2 and a zinc oxide layer 101- are formed on the base 101-1. 3 can be formed. In addition, gas introduction pipes 331 to 334 for introducing sputtering gas are connected to each vacuum vessel. Each vacuum vessel is provided with a film formation region adjusting plate (not shown) for adjusting the contact area between the substrate and the discharge space, and the deposition formed in each vacuum vessel by adjusting this is provided. The film thickness of the film can be adjusted.

  First, the substrate 304 was placed in the deposited film forming apparatus 301, and each vacuum vessel was sufficiently evacuated. Next, sputtering gas was supplied from the gas introduction pipes 331, 332, 333, and 334 while operating the vacuum exhaust system. In this state, the exhaust capacity of the vacuum exhaust system was adjusted, and the pressure in each vacuum vessel was adjusted to a predetermined pressure. The formation conditions are as shown in Table 1.

  When the pressure in each vacuum vessel was stabilized, the substrate started to move from the substrate delivery container 302 toward the substrate take-up container 303. While moving the substrate, an infrared lamp heater (not shown) in each vacuum vessel was operated to adjust the temperature of the film formation surface of the substrate to the values shown in Table 1. A silver target having a purity of 99.99 wt% is used for the cathode electrode 341, and a zinc oxide target containing 0.1 wt% zinc chloride is used for the cathode electrodes 342, 343, and 344, and each cathode is used. Sputtering power shown in Table 1 was applied to the electrodes, a silver reflective layer 101-2 (thickness 800 nm) was deposited on the substrate 101-1, and the zinc oxide layer was deposited in the vacuum containers 312, 313, and 314. 101-3 (thickness 2.0 μm) was deposited to form a substrate 101 having a structure as shown in FIG.

  Next, using the deposited film forming apparatus 401 shown in FIG. 4, the photovoltaic element shown in FIG. 5 was formed by the following procedure. FIG. 5 is a schematic cross-sectional view showing an example of a photovoltaic element having the silicon-based semiconductor of the present invention. In the figure, members similar to those in FIG. The semiconductor layer of this photovoltaic element is composed of an amorphous n-type semiconductor layer 102-1A, an i-type semiconductor layer 102-2A containing a crystalline phase, and a p-type semiconductor layer 102-3A containing a crystalline phase.

  FIG. 4 is a schematic cross-sectional view showing an example of a deposited film forming apparatus for producing the photovoltaic element of the present invention. The deposited film forming apparatus 401 shown in FIG. 4 includes a substrate delivery container 402, semiconductor forming vacuum containers 411 to 416, and a substrate winding container 403 that are connected through gas gates 421 to 427. In the deposited film forming apparatus 401, the belt-like substrate 101 is set through each vacuum vessel and each gas gate. The belt-like substrate 101 is unwound from a bobbin installed in the substrate delivery container 402 and is wound on another bobbin by the substrate take-up container 403.

  Each of the semiconductor forming vacuum vessels 411 to 416 has a deposition chamber. Glow discharge is caused by applying high frequency power from the high frequency power sources 451 to 456 to the discharge electrodes 441 to 446 in the deposition chamber, thereby The source gas is decomposed and a semiconductor layer is deposited on the substrate. In addition, gas introduction pipes 431 to 436 for introducing a source gas and a dilution gas are connected to the respective semiconductor forming vacuum vessels 411 to 416.

  Each vacuum chamber for semiconductor formation of the deposited film forming apparatus 401 shown in FIG. 4 is provided with a film formation region adjusting plate (not shown) for adjusting the contact area between the substrate 101 and the discharge space in each deposition chamber. By adjusting this, the film thickness of each semiconductor film formed in each container can be adjusted.

  Next, a bobbin around which the substrate 101 is wound is attached to the substrate delivery container 402, and the substrate is passed through the gas gate on the carry-in side, the vacuum vessels 411 to 416 for semiconductor formation, and the gas gate on the carry-out side to the substrate take-up container 403. The tension was adjusted so as not to loosen the substrate. Then, the substrate delivery container 402, the semiconductor forming vacuum containers 411 to 416, and the substrate winding container 403 were sufficiently evacuated by an evacuation system including a vacuum pump (not shown).

  Next, the source gas and the dilution gas were supplied from the gas introduction pipes 431 to 436 to the semiconductor forming vacuum vessels 411 to 416 while operating the vacuum exhaust system.

Also, 500 cm ³ / min (normal) of H ₂ gas was supplied to each gas gate from each gate gas supply pipe (not shown). In this state, the exhaust capacity of the vacuum exhaust system was adjusted to adjust the pressure in the semiconductor formation vacuum vessels 411 to 416 to a desired pressure. The formation conditions are as shown in Table 2.

  When the pressure in the semiconductor forming vacuum vessels 411 to 416 was stabilized, the movement of the substrate was started in the direction from the substrate delivery container 402 to the substrate winding container 403.

  Next, high frequency power is introduced from the high frequency power sources 451 to 456 to the discharge electrodes 441 to 446 in the semiconductor forming vacuum vessels 411 to 416 to cause glow discharge in the deposition chamber in the semiconductor forming vacuum vessels 411 to 416, An amorphous n-type semiconductor layer (film thickness: 50 nm), an i-type semiconductor layer containing a crystal phase (film thickness: 3.5 μm), and a p-type semiconductor layer containing a crystal phase (film thickness: 10 nm) are formed on the surface. An element was formed, and the formed strip-like photovoltaic element was processed into a 36 cm × 22 cm solar cell module using a continuous modularization apparatus (not shown) (Example 1).

  Next, a solar cell module was prepared in the same procedure as in Example 1 except that a zinc oxide target not containing zinc chloride was used for the cathode electrodes 342, 343, and 344 (Comparative Example 1-1). ).

  Next, a solar cell module was prepared in the same procedure as in Example 1 except that a zinc oxide target containing 2 wt% aluminum was used for the cathode electrodes 342, 343, and 344 (comparison). Example 1-2).

The amount of chlorine atoms contained in the zinc oxide layer prepared in Example 1 is 5.0 × 10 ¹⁸ cm ^{−3 as} a result of SIMS analysis, and is included in Comparative Example 1-1 and Comparative Example 1-2. The amount of chlorine atoms produced was 1.0 × 10 ¹⁷ cm ⁻³ or less.

Next, the photoelectric conversion efficiency of the solar cell modules prepared in Example 1, Comparative Example 1-1, and Comparative Example 1-2 was measured using a solar simulator (AM1.5, 100 mW / cm ² ). As a result, the photoelectric conversion efficiency of the solar cell module of Example 1 was 1.12 times and 1.08 times the photoelectric conversion efficiency of the solar cell modules of Comparative Example 1-1 and Comparative Example 1-2, respectively. The solar cell module of Example 1 was superior in that the short-circuit current density was large and the series resistance was small as compared with the solar cell module of Comparative Example 1-1. Moreover, compared with the solar cell module of Comparative Example 1-2, it turns out that the short circuit current density is excellent and the incident light was able to be absorbed efficiently with the semiconductor layer. As for the surface shape of the zinc oxide layer formed in Comparative Example 1-2, the uneven shape was smaller than the surface shape of the zinc oxide layer of Example 1.

Moreover, when the chlorine atom contained in the semiconductor layer of the solar cell module of Example 1 was investigated by SIMS analysis, the maximum value was 1.0 × 10 ¹⁷ cm ⁻³ or less, and the chlorine atom contained in the zinc oxide layer It was 1/10 or less of the maximum value of content.

  From the above, it can be seen that the solar cell module including the photovoltaic element of the present invention has excellent features.

(Example 2)
A solar cell module in the same procedure as in Example 1 except that the amount of zinc chloride contained in the target used for the cathode electrodes 342, 343, 344 is changed from 0.05 wt% to 0.5 wt%. The amount of chlorine atoms contained in the zinc oxide layer was determined by SIMS analysis, and the photoelectric conversion efficiency of the solar cell module was measured. Table 3 shows the measurement results.

As shown in Table 3, those having a chlorine atom amount in the zinc oxide layer of 1.0 × 10 ¹⁸ cm ⁻³ or more and 5.0 × 10 ¹⁹ cm ⁻³ or less show excellent photoelectric conversion efficiency. . When the chlorine content exceeded 5.0 × 10 ¹⁹ cm ⁻³ , the short-circuit current value decreased. From the above, it can be seen that the solar cell module including the photovoltaic element of the present invention has excellent features.

(Example 3)
The amounts of zinc chloride contained in the targets used for the cathode electrodes 342, 343, and 344 are 0.07 wt%, 0.1 wt%, and 0.07 wt%, respectively, and the content of chlorine atoms in the zinc oxide layer The photovoltaic element was formed in the same procedure as in Example 1 except that the solar cell module was changed.

As a result of SIMS analysis, the amount of chlorine atoms contained in the zinc oxide layer prepared in Example 3 was 1.0 × 10 ¹⁸ cm ⁻³ on the reflective layer side and the semiconductor layer side, and 5. It was 0 × 10 ¹⁸ cm ⁻³ .

  Next, when the photoelectric conversion efficiency of the solar cell module was measured, the photoelectric conversion efficiency 1.05 times that of the solar cell module of Example 1 was obtained. From the above, it can be seen that the solar cell module including the photovoltaic element of the present invention in which the content of chlorine atoms in the zinc oxide layer has a maximum value in the film has more excellent features.

Example 4
The zinc oxide layer has a two-layer structure as shown in FIG. 2B, and the first zinc oxide layer 101-3A is formed to a thickness of 300 nm by a sputtering method using a zinc oxide target, and the second zinc oxide layer 101- A photovoltaic element was formed by the same method as in Example 3 except that 3B was formed by 1.7 μm by an electrodeposition method (Example 4-1).

Here, when the first zinc oxide layer is formed, a target in which the amount of zinc chloride contained in the target is 0.07% by weight and 0.1% by weight as in Example 3 is used. The amount of chlorine atoms contained in the first zinc oxide layer is 1.0 × 10 ¹⁸ cm ^{−3 at} the reflective layer side and the second zinc oxide layer side, and 5.0 × 10 ¹⁸ cm ⁻³ at the middle portion of the film. It formed so that it might become.

  The second zinc oxide layer 101-3B was formed using the deposited film forming apparatus 601 shown in FIG. FIG. 6 is a schematic cross-sectional view showing an example of a deposited film forming apparatus for manufacturing a substrate containing zinc oxide according to the present invention. The deposited film forming apparatus 601 shown in FIG. 6 includes a feed roller 602, three forming containers 611-1, 611-2, 611-3, a water washing container 613, a drying container 615, and a take-up roller 603. In this deposited film forming apparatus 601, a substrate with a belt-like reflective layer is set through each container. The belt-shaped substrate is unwound from a bobbin installed on the feed roller 602 and wound on another bobbin by the take-up roller 603. Zinc counter electrodes 621-1, 621-2, and 621-3 are provided in the forming containers 611-1, 611-2, and 611-3, and this counter electrode includes a load resistor and a power source 631- 1, 631-2, 631-3. Further, by using a heater and a thermocouple (not shown), the temperature is monitored while stirring the solution, and the temperature of the aqueous solution in the forming containers 611-1, 611-2, 611-3 can be adjusted. . Further, the aqueous solution on the substrate surface is washed away with a washing container 613 using an ultrasonic device (not shown), pure water is washed with a pure water shower 614 at the outlet side of the washing container, and an infrared heater 616 is used with the drying container 615. The substrate surface can be dried. Further, in the configuration in which a plurality of forming containers are arranged in series as shown in FIG. 6, it is possible to take a method of forming a zinc oxide layer under different conditions for each forming container.

The aqueous solution in the forming containers 611-1, 611-2, 611-3 is a zinc ion concentration of 0.15 mol / l, pH = 5.0, an aqueous solution temperature of 85 ° C., and a current value flowing between the anode and the cathode is 15 mA / cm. ^2. Add dextrin concentration of 0.10 g / l and potassium hydrogen phthalate to make the phthalic acid concentration 30 μmol / l and start transporting the substrate to form the second zinc oxide layer (thickness 1.7 μm). I did it. Here, hydrochloric acid is added to the solutions in the forming containers 611-1 and 611-3 to adjust the concentration of chlorine atoms in the aqueous solution to 5 μmol / l, and the solution in the forming container 611-2 has a concentration of chlorine atoms in the aqueous solution. It was prepared as 100 μmol / l.

The substrate taken up by the take-up roller was placed in a drying container (not shown) connected to a vacuum pump, and dried in a 10 kPa nitrogen atmosphere at 250 ° C. for 5 hours. When the second zinc oxide layer was examined by SIMS analysis, the central portion contained 1.0 × 10 ¹⁹ cm ⁻³ of chlorine atoms, and both ends were 1.0 × 10 ¹⁸ cm ⁻³ of chlorine atoms. Was included.

Next, a photovoltaic element was formed in the same manner as in Example 4-1, except that the concentration of chlorine atoms in the aqueous solution of the forming vessel 611-2 was set to 20 μmol / l, thereby producing a solar cell module (implementation). Example 4-2). When the second zinc oxide layer was examined by SIMS analysis, the central part contained 3.0 × 10 ¹⁸ cm ⁻³ chlorine atoms, and both ends contained 1.0 × 10 ¹⁸ cm ⁻³ chlorine atoms. Was included.

Next, a photovoltaic element was formed in the same manner as in Example 4-1, except that the second zinc oxide layer was formed without adding hydrochloric acid in the aqueous solution, thereby producing a solar cell module (implementation). Example 4-3). At this time, when the second zinc oxide layer was examined by SIMS analysis, the amount of chlorine atoms was 1.0 × 10 ¹⁷ cm ⁻³ or less.

  When the photoelectric conversion efficiency of the solar cell module formed in Example 4-1, Example 4-2, and Example 4-3 was measured, each solar cell module was compared with the solar cell module of Comparative Example 1-1. Excellent photoelectric conversion efficiency was obtained. In particular, the solar cell of Example 4-1 in which the maximum value of the content of chlorine atoms contained in the first zinc oxide layer is smaller than the maximum value of the content of chlorine atoms contained in the second zinc oxide layer The module had better photoelectric conversion efficiency. From the above, it can be seen that the solar cell module including the photovoltaic element of the present invention has excellent features.

It is typical sectional drawing which shows an example of the photovoltaic element of this invention. It is typical sectional drawing which shows an example of the board | substrate containing the zinc oxide layer of this invention. It is typical sectional drawing which shows an example of the deposited film formation apparatus which manufactures the board | substrate containing the zinc oxide layer of this invention. It is typical sectional drawing which shows an example of the deposited film formation apparatus which manufactures the photovoltaic element of this invention. It is typical sectional drawing which shows an example of the photovoltaic device which has a silicon-type semiconductor of this invention. It is typical sectional drawing which shows an example of the deposited film formation apparatus which manufactures the board | substrate containing the zinc oxide of this invention.

Explanation of symbols

101: Substrate 101-1: Base 101-2: Reflective layer 101-3: Zinc oxide layer 101-3A: First zinc oxide layer 101-3B: Second zinc oxide layer 102-1: n-type semiconductor layer 102 -1A: amorphous n-type semiconductor layer 102-2: i-type semiconductor layer 102-2A: i-type semiconductor layer 102-3 including crystal phase: p-type semiconductor layer 102-3A: p-type semiconductor layer including crystal phase 103: transparent conductive layer 104: current collecting electrode 301: deposited film forming apparatus 302: substrate delivery container 303: substrate take-up containers 311 to 314: vacuum containers 331 to 334: gas introduction pipes 341 to 344: cathode electrodes 351 to 354: DC power supply 401: Deposited film forming apparatus 402: Substrate delivery container 403: Substrate winding container 411-416: Semiconductor forming vacuum containers 421-427: Gas gates 431-436: Gas Inlet pipes 441 to 446: discharge electrodes 451 to 456: high frequency power source 601: deposited film forming apparatus 602: delivery roller 603: take-up roller 611: forming container 613: washing container 614: pure water shower 615: drying container 616: infrared heater 621 : Counter electrode 631: Power supply

Claims (7)

A zinc oxide layer formed on a substrate, wherein the zinc oxide layer contains 1.0 × 10 ¹⁸ cm ⁻³ or more and 5.0 × 10 ¹⁹ cm ⁻³ or less of chlorine atoms. Zinc oxide layer to do. A photovoltaic element formed by laminating at least a zinc oxide layer and a semiconductor layer on a substrate, wherein the zinc oxide layer is 1.0 × 10 ¹⁸ cm ⁻³ or more and 5.0 × 10 ¹⁹ cm ⁻³ or less. A photovoltaic element characterized by containing a chlorine atom.   3. The photovoltaic element according to claim 2, wherein the chlorine atom in the zinc oxide layer changes in content in the thickness direction of the zinc oxide layer and has a maximum value in the film. .   The photovoltaic element according to claim 3, wherein the zinc oxide layer has a plurality of the maximum values.   5. The photovoltaic according to claim 4, wherein, among the plurality of maximum values included in the zinc oxide layer, a maximum value existing on the substrate side is smaller than a maximum value existing on the semiconductor layer side. Power element.   6. The maximum value of the chlorine atom content contained in the semiconductor layer is smaller than the maximum value of the chlorine atom content contained in the zinc oxide layer. The photovoltaic device according to Item.   The maximum value of the chlorine atom content contained in the semiconductor layer is 1/10 or less of the maximum value of the chlorine atom content contained in the zinc oxide layer. Photovoltaic element.

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