JP2009206348A - Method of manufacturing chalcopyrite type solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of efficiently manufacturing a chalcopyrite type solar cell. <P>SOLUTION: A DC sputter method is used for forming a transparent electrode layer on a buffer layer. At this moment, a spaced distance and a pressure are set so that the product of a distance (spaced distance) between a target and a glass substrate and a supply gas pressure may be 4.8 cm Pa or less because a ratio of particles having energy not less than 10 eV in the particles evaporated from the target is to be not less than 7%. Further, heat treatment is performed after the transparent electrode layer is formed to repair defects such point defects present in the crystal structure of a buffer layer, a light absorbing layer, or the transparent electrode layer for restoration of the original crystal structure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a chalcopyrite solar cell including a chalcopyrite light absorption layer.

  FIG. 5 is a structural explanatory view schematically showing a longitudinal section of a general chalcopyrite solar cell. In this case, the chalcopyrite solar cell 10 includes a lower electrode layer 14 formed on the glass substrate 12, a light absorption layer 16 that is a p-type semiconductor made of a chalcopyrite compound such as Cu (In, Ga) Se, The buffer layer 18 made of an n-type semiconductor and the transparent electrode layer 20 made of an n-type semiconductor are configured as a laminated body laminated in this order. In FIG. 5, reference numerals 22 and 24 denote current collecting electrodes.

  Suitable materials for the lower electrode layer 14 include Mo or W, and suitable materials for the buffer layer 18 include CdS, ZnS, InS, and the like.

  On the other hand, the transparent electrode layer 20 is a transparent body that transmits sunlight or the like. Therefore, the material of the transparent electrode layer 20 is selected to have excellent light transmission and high current collection efficiency. As this type of material, ZnO: Al in which ZnO is doped with Al is known.

  Here, when forming the transparent electrode layer 20 on the buffer layer 18, the MOCVD method and the RF sputtering method are often employed. The reason for this is that according to these methods, the concern that the buffer layer 18 or the light absorption layer 16 is damaged is eliminated, and therefore the chalcopyrite solar cell is caused by the damage of the buffer layer 18 or the light absorption layer 16. This is because it is possible to avoid the deterioration of the ten characteristics.

  However, the MOCVD method and the RF sputtering method have a drawback that the film formation rate is low, and it is difficult to efficiently mass-produce the chalcopyrite solar cell 10 for this reason. Moreover, in these methods, there is a problem that it is not easy to make the thickness of the film substantially equal when providing a film having a large area.

  In order to eliminate this problem, Patent Document 1 discloses that a transparent electrode layer having a small film thickness is first formed by RF sputtering, and then a DC sputtering method having a relatively high film forming speed is performed. It has been proposed to form a film with a predetermined thickness. In this case, the small transparent electrode layer formed first functions as a protective layer for protecting the buffer layer or the light absorption layer during the DC sputtering.

  In Patent Document 2, after employing the DC sputtering method, the output voltage is initially reduced when the transparent electrode layer is formed, and the output power is increased as the thickness of the transparent electrode layer is increased. It has been proposed.

JP-A-11-284211 International Publication No. WO2003 / 009394 Pamphlet

  The prior art described in Patent Document 1 needs to be provided with two mechanisms, an RF sputtering mechanism and a DC sputtering mechanism. Of course, since an RF power source and a DC power source and a control system for controlling the power source are also required, the configuration of the apparatus becomes complicated and the capital investment increases.

  In addition, it is difficult to say that the DC sputtering method is a method with a sufficient film forming speed. Therefore, when the conventional techniques described in Patent Documents 1 and 2 are adopted as they are, it is easy to efficiently mass-produce chalcopyrite solar cells. I guess it is not.

  The present invention has been made to solve the above-described problems, and can easily repair defects generated in a buffer layer or a light absorption layer, and can form a transparent electrode layer with a simple facility. An object of the present invention is to provide a method for manufacturing a chalcopyrite solar cell capable of increasing the size of the solar cell.

To achieve the above object, the present invention provides a method for producing a chalcopyrite solar cell comprising a chalcopyrite light absorption layer,
Forming a first electrode above the substrate;
Forming a chalcopyrite type light absorption layer above the first electrode;
Forming a buffer layer above the chalcopyrite light absorption layer;
Forming a second electrode by sputtering above the buffer layer;
Performing a heat treatment after forming the second electrode;
It is characterized by having.

  By performing the heat treatment, defects such as a point defect existing in the crystal structure of the buffer layer, the light absorption layer, or the second electrode are repaired. That is, the crystals forming these layers are restored to the original crystal structure.

  In short, according to the present invention, even when the buffer layer or the light absorption layer is damaged when forming the second electrode, the damage can be recovered. Therefore, a chalcopyrite solar cell excellent in various properties such as conversion efficiency can be obtained.

  In addition, since the second electrode is formed by sputtering, the second electrode can be formed efficiently. That is, the production efficiency of the chalcopyrite solar cell is improved.

  As understood from the above, according to the present invention, a chalcopyrite solar cell excellent in various characteristics can be mass-produced efficiently. In addition, since existing simple equipment can be used, capital investment does not increase.

  In forming the second electrode, it is preferable to employ a DC sputtering method having a relatively high film formation rate. Of course, also in this case, defects generated in the buffer layer and the light absorption layer are repaired by the heat treatment.

  Here, the sputtering for forming the second electrode is preferably performed under the condition that the product of the distance between the target and the substrate and the pressure of the supply gas is 4.8 cm · Pa or less. When the second electrode is formed under such conditions, the second electrode becomes dense and the film formation rate increases. Moreover, the coverage is good. In addition, in this case, the crystal grain boundary between the crystals constituting the second electrode becomes unclear. That is, the crystals are well fused. Accordingly, the interface resistance at the grain boundary is reduced.

  For the above reasons, the resistance of the second electrode is reduced, so that a chalcopyrite solar cell with high conversion efficiency can be obtained.

  The material of the buffer layer is preferably InS. This is because InS has a relatively low melting point, so that defect repair by heat treatment is relatively easy.

  The heat treatment may be performed in the air, but is preferably performed in a vacuum atmosphere, an inert gas atmosphere, or a reducing gas atmosphere. In this case, it is possible to reliably avoid oxidation of each layer constituting the chalcopyrite solar cell. Therefore, it is possible to prevent the resistance of the chalcopyrite solar cell from increasing.

  According to the present invention, since the heat treatment is performed after the second electrode is formed, a point defect is formed in the crystal structure constituting the buffer layer or the light absorption layer in accordance with the sputtering at the time of forming the second electrode. Even when the buffer layer or the light absorption layer is damaged, such as when a defect such as the above occurs, the damage is recovered. Therefore, a chalcopyrite solar cell excellent in various characteristics such as conversion efficiency can be easily obtained.

  Moreover, since sputtering with a high deposition rate is employed when forming the second electrode, the production efficiency of the chalcopyrite solar cell is also improved. As a result, chalcopyrite solar cells excellent in various characteristics can be mass-produced efficiently.

  Hereinafter, preferred embodiments of the method for producing a chalcopyrite solar cell according to the present invention will be described in detail with reference to the accompanying drawings. The same components as those shown in FIG. 5 are denoted by the same reference numerals, and detailed description thereof is omitted.

  1A to 1E are process flow explanatory views schematically showing the manufacturing process of the chalcopyrite solar cell 10. When producing the chalcopyrite solar cell 10, first, as shown in FIG. 1A, for example, by performing sputtering film formation, the lower electrode layer 14 (first electrode) made of Mo or the like is formed on the glass substrate 12. Form a film.

  Next, as shown in FIG. 1B, a precursor layer 30 containing Cu, In, and Ga is provided by sputtering film formation or the like.

  Then, for example, an alkaline solution such as a sodium salt aqueous solution such as a sodium chloride aqueous solution is applied to the upper end surface of the precursor layer 30, and then the solution is dried, as shown in FIG. An alkali layer 32 is formed thereon. The solution is applied by spin coating or the like. Or you may make it immerse the semi-finished product in which the precursor layer 30 was formed in the said solution.

Next, the semi-finished product on which the alkali layer 32 is formed is housed in a heat treatment furnace, preheated, and then the precursor layer 30 is selenized by introducing H ₂ Se gas into the heat treatment furnace, as shown in FIG. 1D. In addition, a light absorption layer 16 made of Cu (In, Ga) Se which is a chalcopyrite compound, that is, so-called CIGS is provided. At this time, an alkali component such as Na contained in the alkali layer 32 promotes crystallization of Cu (In, Ga) Se. The alkali layer 32 finally diffuses into the light absorption layer 16 and disappears, and as a result, the upper end surface of the light absorption layer 16 is exposed.

  Thereafter, a buffer layer 18 made of CdS, ZnS, InS or the like, which is an n-type semiconductor, is formed by a chemical bath deposition method or the like. Of these, InS having the lowest melting point is preferred. In this case, even if a defect occurs in the buffer layer 18, the defect is easily repaired during the heat treatment described later.

  Further, after performing mechanical scribing, an n-type transparent electrode layer 20 (second electrode) is formed as shown in FIG. 1E. In this embodiment, a DC sputtering method is employed in which the transparent electrode layer 20 is formed on the buffer layer 18 by sputtering a target.

  Here, the DC sputtering method is performed by varying the separation distance between the target and the glass substrate 12 and the pressure of the supply gas to evaporate the particles from the target surface, and the energy of 10 eV or more existing in the particles is obtained. FIG. 2 shows the result of examining the ratio of those possessed. From FIG. 2, when the product of the separation distance between the target and the glass substrate 12 and the pressure of the supply gas (hereinafter also referred to as “separation distance / pressure product”) is 4.8 cm · Pa or less, 10 eV It is understood that the ratio of particles having the above energy is 7% or more.

  Particles evaporated from the target surface are less likely to scatter as the energy increases. That is, the film formation rate of the transparent electrode layer 20 can be increased as the distance between the target and the glass substrate 12 is reduced and the pressure of the supply gas is reduced.

  Further, FIGS. 3 and 4 show simulation results of the angular distribution at the time of starting the target of the particles when the pressure of the supply gas is 0.1 Pa and 2.0 Pa, and the angular distribution when reaching the buffer layer 18, respectively. 3 and 4, the angle distribution of the particles at the start of the target is substantially equal to each other, but the frequency of the particles in the low angle region and the high angle region in the angle distribution of the particles when reaching the buffer layer 18 is supplied. It can be seen that the gas pressure decreases as the gas pressure decreases. Thus, the decrease in the frequency of the particles in the low angle region and the high angle region indicates that the coverage is improved even when the buffer layer 18 has irregularities when the transparent electrode layer 20 is formed.

  From the above results, in the present embodiment, the distance between the target and the glass substrate 12 and the pressure of the supply gas are set so that the separation distance / pressure product is 4.8 cm · Pa or less. As a result, the proportion of particles having an energy of 10 eV or more in the particles evaporated from the target surface is relatively large. As a result, the particles evaporated from the target surface and the supply gas atoms recoiled on the target surface are in the gas phase. The probability of scattering is reduced. That is, the target is efficiently sputtered by the supply gas atoms, and the transparent electrode particles generated by the sputtering efficiently reach the buffer layer 18.

  That is, by setting the separation distance / pressure product to 4.8 cm · Pa or less, the transparent electrode layer 20 can be efficiently formed by the DC sputtering method until a predetermined thickness is reached. In addition, since the transparent electrode layer 20 becomes dense, the film density increases, so the resistance of the transparent electrode layer 20 decreases.

  In addition, in this case, since the coverage of the transparent electrode particles efficiently reaches the buffer layer 18, the coverage is improved. Therefore, even when the buffer layer 18 has fine unevenness, the unevenness is reduced. A substantially flat transparent electrode layer 20 is formed by coating. In such a transparent electrode layer 20, resistance in a direction substantially orthogonal to the film forming direction (thickness direction), that is, a so-called in-plane direction is also reduced.

  In addition, the crystal grain boundary between the crystals constituting the transparent electrode layer 20 becomes unclear. That is, since the crystals are fused well, it becomes a denser layer. As a result, the resistance is further reduced, so that the chalcopyrite solar cell 10 with further improved conversion efficiency can be obtained.

  The above tendency becomes more prominent when the separation distance / pressure product is 3.2 cm · Pa or less.

  Thus, according to this Embodiment, since the low-resistance transparent electrode layer 20 can be obtained in a short time, the chalcopyrite solar cell 10 excellent in power generation characteristics can be efficiently mass-produced.

  As the transparent electrode layer 20 is formed as described above, the buffer layer 18 is slightly damaged, and there is a concern that defects such as point defects may occur in the crystal structure. In some cases, the transparent electrode layer 20 may also be defective. If these defects remain in the buffer layer 18 and the transparent electrode layer 20, the resistance in the chalcopyrite solar cell 10 increases.

  Therefore, next, annealing is performed to restore the original crystal structure. Specifically, after forming the transparent electrode layer 20, the whole is subjected to heat treatment.

  The heat treatment may be performed in the air, but it is preferable that the chalcopyrite solar cell 10 is housed in a heat treatment furnace and the atmosphere is a vacuum, an inert gas, or a reducing gas. By selecting such an atmosphere, it is possible to reliably avoid that each layer constituting the chalcopyrite solar cell 10 undergoes a chemical change (particularly oxidation) and becomes a different substance exhibiting high resistance. Examples of the inert gas include nitrogen and argon. On the other hand, examples of the reducing gas include hydrogen and a mixed gas of hydrogen and an inert gas.

  By performing the heat treatment, atomic diffusion and partial melting / resolidification occur in the microstructure of the buffer layer 18, and as a result, the defect is repaired and the buffer layer 18 is recovered. This defect repair proceeds more easily as the material of the buffer layer 18 has a lower melting point. Therefore, as a material of the buffer layer 18, InS is suitable as described above.

  If the temperature during the heat treatment is excessively lowered, it becomes difficult to repair defects in the buffer layer 18. On the other hand, when the temperature exceeds 225 ° C., thermal stress may be applied to the chalcopyrite solar cell 10, and Cu in CIGS, which is the material of the light absorption layer 16, may diffuse into the buffer layer 18. When such a situation occurs, the chalcopyrite solar cell 10 has low conversion efficiency.

  Therefore, the temperature during the heat treatment is preferably in the range of 150 to 225 ° C. In this case, a holding time of 20 to 180 minutes is sufficient.

  Of course, even if a defect occurs in the light absorption layer 16, it is simultaneously repaired by the heat treatment.

  As described above, even if the buffer layer 18 or the light absorption layer 16 is damaged when the transparent electrode layer 20 is formed by the DC sputtering method, defects in the buffer layer 18 or the light absorption layer 16 are caused by the heat treatment. Since it is repaired, it can be avoided that various characteristics of the chalcopyrite solar cell 10 are deteriorated. For example, when the resistance of the transparent electrode layer 20 in the chalcopyrite solar cell 10 that has not been heat-treated is 1, the heat-treated one has 0.8 even if it has been treated in the atmosphere. Lower than 0.7 for those treated in a vacuum atmosphere, an inert gas atmosphere, or a reducing gas atmosphere.

  After all, according to the present embodiment, chalcopyrite solar cell 10 having excellent power generation characteristics can be easily mass-produced.

  The heat treatment may be performed after the transparent electrode layer 20 is formed, or may be performed after the current collecting electrodes 22 and 24 (see FIG. 5) are formed.

  In the above-described embodiment, the alkali layer 32 is provided on the precursor layer 30, but the alkali layer 32 may be provided on the lower electrode layer 14. The alkali layer 32 is not particularly limited to one containing Na, and may contain another kind of alkali element such as K. Of course, the raw material for providing the alkali layer 32 is not particularly limited to the sodium salt aqueous solution, and may be a potassium salt aqueous solution.

  Furthermore, the material of the lower electrode layer 14 may be a metal other than Mo, for example, W.

  Furthermore, for example, another layer may be interposed between the glass substrate 12 and the lower electrode layer 14. Examples of this type of layer include a layer for mitigating thermal expansion coefficient mismatch.

1A to 1E are process flow explanatory views schematically showing a manufacturing process of a chalcopyrite solar cell. FIG. 5 is a chart showing a ratio of particles having energy of 10 eV or more existing in particles evaporated from the target surface when the DC sputtering method is performed by changing the separation distance between the target and the glass substrate and the pressure of the supply gas. is there. It is the simulation result of the angular distribution at the time of the target departure of the particle | grains when the pressure of supply gas is 0.1 Pa, and the angular distribution at the time of buffer layer arrival. It is the simulation result of the angular distribution at the time of the target departure of the particle | grains when the pressure of supply gas is 2.0 Pa, and the angular distribution at the time of buffer layer arrival. It is structure explanatory drawing which showed the longitudinal cross-section of the general chalcopyrite type | mold solar cell typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Chalcopyrite type solar cell 12 ... Glass substrate 14 ... Lower electrode layer 16 ... Light absorption layer 18 ... Buffer layer 20 ... Transparent electrode layer 30 ... Precursor layer 32 ... Alkali layer

Claims (4)

A method for producing a chalcopyrite solar cell comprising a chalcopyrite light absorption layer,
Forming a first electrode above the substrate;
Forming a chalcopyrite type light absorption layer above the first electrode;
Forming a buffer layer above the chalcopyrite light absorption layer;
Forming a second electrode by sputtering above the buffer layer;
Performing a heat treatment after forming the second electrode;
A method for producing a chalcopyrite solar cell, comprising:   2. The manufacturing method according to claim 1, wherein sputtering when forming the second electrode is performed under a condition that a product of a separation distance between the target and the substrate and a pressure of a supply gas is a value of 4.8 cm · Pa or less. A method for producing a chalcopyrite solar cell.   3. The method for manufacturing a chalcopyrite solar cell according to claim 1, wherein an InS layer is formed as the buffer layer.   The manufacturing method of any one of Claims 1-3 WHEREIN: The said heat processing is performed in a vacuum atmosphere, inert gas atmosphere, or reducing gas atmosphere, The manufacturing method of the chalcopyrite solar cell characterized by the above-mentioned.

Images