TW201705506A - Cigs solar cell and manufacturing method for the same - Google Patents

Abstract

To provide a CIGS solar cell including a CIGS layer with the excellent characteristics and a manufacturing method for the same. The CIGS solar cell includes a substrate 1, a back electrode layer 3, a CIGS light absorption layer 4, a buffer layer 5, and a transparent electrode 6 in this order. The CIGS light absorption layer 4 includes a first light absorption layer 4a formed on the substrate 1 side, and a second light absorption layer 4b formed on the first light absorption layer 4a. The first light absorption layer 4a includes crystal grains with an average grain size of A and the second light absorption layer 4b includes microscopic crystal grains with an average grain size of A/3 or less.

Description

CIGS solar battery and its manufacturing method Field of invention

The present invention relates to a CIGS solar cell having a CIGS light absorbing layer having good characteristics and a method of manufacturing the same.

Background of the invention

Compared with the conventional crystalline solar cell, a thin solar cell represented by an amorphous germanium solar cell and a compound solar cell can significantly reduce material cost and manufacturing cost. Therefore, in recent years, these research and development departments have been rapidly progressing. In particular, the elements of Group I, Group III, and Group VI are used as a compound solar cell of a constituent material, and the light absorbing layer is made of copper (Cu), indium (In), gallium (Ga), and selenium (Se) alloys. The CIGS solar cell is particularly attractive for thin solar cells because it does not use germanium at all and has excellent photoelectric conversion efficiency (hereinafter referred to as "conversion efficiency").

Such a CIGS solar cell generally has a structure in which a substrate, a back electrode layer, a CIGS light absorbing layer, a buffer layer, and a transparent electrode layer are sequentially laminated, and the interface between the CIGS light absorbing layer and the buffer layer is formed by pn bonding. In addition, it is considered that it is necessary to increase the crystal size of the CIGS light absorbing layer to a high quality and to achieve high conversion efficiency (for example, refer to Patent Document 1).

Further, Patent Document 2 discloses that in the crystal growth step of the CIGS light absorbing layer, the metal precursor layer is heat-treated in a Se flux environment by forming a Cu excess composition (Cu/(Ga+In)>1). It grows into a crystal of the chalcopyrite structure. At this time, the Cu-Se-based liquid phase functions as a flux for promoting crystallization of the CIGS light absorbing layer. Then, after the crystal is sufficiently grown, the final composition of the layer is made into an (In, Ga) excess composition (Cu/(Ga+In)<1) by adding In, Ga, and Se flux, but in the addition of In In the step of the Ga or Se flux, when the Cu-Se system starts to be insufficient, the crystal growth is insufficient, and minute crystal grains having an average particle diameter of 50 nm or more and 300 nm or less (the average particle diameter of the main body is 1000 nm or more) are formed. It is considered that when such a minute crystal grain exists in the CIGS light absorbing layer, the conversion efficiency of the solar cell is low.

On the other hand, in order to increase the particle size of the crystals in the CIGS light absorbing layer or to form fine crystal grains, it is possible to observe a certain degree of improvement in conversion efficiency, and to improve the general market, The conversion efficiency obtained by the countermeasures is insufficient, and the current situation requires the development of CIGS solar cells with higher conversion efficiency.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Publication No. 10-513606

Patent Document 2: Japanese Laid-Open Patent Publication No. 2013-58540

Summary of invention

The present invention has been made in view of such circumstances, and an object thereof is to provide a CIGS solar cell capable of achieving higher conversion efficiency and a method of manufacturing the same.

In order to achieve the above object, a first aspect of the present invention provides a CIGS solar cell having a substrate, a back electrode layer, a CIGS light absorbing layer, a buffer layer, and a transparent electrode layer in sequence; wherein the CIGS light absorbing layer is formed a first light absorbing layer on the substrate side and a second light absorbing layer formed on the first light absorbing layer, wherein the first light absorbing layer is composed of crystal grains having an average particle diameter A, and The second light absorbing layer is composed of minute crystal grains having an average particle diameter of A/3 or less.

In the above-mentioned CIGS solar cell, the average particle diameter of the crystal grains constituting the first light absorbing layer is 1000 nm or more and 2000 nm or less, and the average particle diameter of the minute crystal grains constituting the second light absorbing layer is 50 nm. Above and below 300 nm.

According to a third aspect of the invention, in the CIGS solar cell, the thickness of the second light absorbing layer is 50 nm or more and 200 nm or less.

Further, a fourth aspect of the present invention provides a method for manufacturing a CIGS solar cell, which is a method for manufacturing a CIGS solar cell having a substrate, a back electrode layer, a CIGS light absorbing layer, a buffer layer, and a transparent layer. In the electrode layer, the CIGS light absorbing layer is composed of a first light absorbing layer formed on the substrate side and a second light absorbing layer formed on the first light absorbing layer, wherein the first light absorbing layer is averaged The crystal grain of the particle diameter A is formed, and the second light absorbing layer is composed of fine crystal grains having an average particle diameter of A/3 or less; and the manufacturing method is to form the CIGS light absorbing layer by the following steps: On the substrate, a layer ( α ) containing indium, gallium, and selenium, and a layer ( β ) containing copper and selenium are sequentially laminated in a solid phase state, and a layer of layers ( α ) and layers ( β ) is laminated. a step of heating the crystal to form a first light absorbing layer composed of crystal grains having an average particle diameter A; and supplying indium, gallium, and selenium to the first light absorbing layer in a gas phase state by At the same time, the supply and crystal growth of indium, gallium and selenium are formed to form The second light absorbing layer composed of minute crystal grains having an average particle diameter of A/3 or less.

That is, the inventors of the present invention have repeatedly focused on the crystallization of the CIGS light absorbing layer in order to obtain a CIGS solar cell having a high conversion efficiency. As a result, it was found that, in contrast to the flow rate of the crystals constituting the CIGS light absorbing layer and the flow of the fine crystal grains, which were previously discussed in order to achieve high conversion efficiency, the CIGS light absorbing layer was internally filled with minute crystal grains and When the specific portion of the CIGS light absorbing layer is disposed in the minute crystal grains, the high conversion efficiency of the CIGS solar cell can be unexpectedly achieved, and the present invention has been conceived.

Further, in the present invention, the term "solid phase" means a phase which is solid at its temperature, and the term "liquid phase" means a phase which is in a liquid state at its temperature. Further, the term "gas phase" means a phase which is in a gaseous state at its temperature.

Further, in the average particle diameter of the crystal particles constituting the light absorbing layer of the present invention, the first and second observations can be observed by using an SEM (Scanning Electron Microscope) and setting the center portion thereof to 20,000 times. The cross section of each of the light absorbing layers can be determined by measuring the particle diameter of all the crystals on the screen and calculating the average. When the crystal is spherical, the above-mentioned particle diameter is measured for its diameter, and in other shapes, the maximum length is measured.

That is, the CIGS solar cell of the present invention has a substrate, a back electrode layer, a CIGS light absorbing layer, a buffer layer, and a transparent electrode layer in sequence; the CIGS light absorbing layer is formed of a first light absorbing layer formed on the substrate side, and The second light absorbing layer is formed on the first light absorbing layer, wherein the first light absorbing layer is composed of crystal grains having an average particle diameter A, and the second light absorbing layer is formed by an average particle diameter A/ 3 or less of fine crystal grains. Therefore, it is possible to extract electrons not only by electrons generated by the first light absorbing layer composed of crystal grains having a large average particle diameter disposed on the substrate side but also by the average particles disposed on the side of the buffer layer. The small crystal grain having a small diameter constitutes the second light absorbing layer, and a large amount of Na present in the crystal grain boundary of the CIGS can be supplied in a large amount to the vicinity of the surface of the CIGS light absorbing layer (on the side where the light is incident), so that the vicinity can be received. The acceptor concentration is increased.

Further, in the CIGS light absorbing layer, fine irregularities formed by minute crystal grains of the second light absorbing layer are formed on the surface (the side on which the light is incident), and the fine unevenness is used to close the light. It is also expected to increase the current value of the CIGS solar cell.

In addition, when the average particle diameter of the crystal grains constituting the first light absorbing layer is 1000 nm or more and 2000 nm or less, and the average particle diameter of the fine crystal grains constituting the second light absorbing layer is 50 nm or more and 300 nm or less, the current value is further Upgraded to become a high conversion efficiency CIGS solar cell.

In addition, when the thickness of the second light absorbing layer is 50 nm or more and 200 nm or less, the second light absorbing layer composed of minute crystal grains is formed thin on the surface side of the CIGS light absorbing layer, so that CIGS light is used. Suck The surface of the layered surface (the incident surface of the light) is formed with fine irregularities, and the effect of shutting off the light by the fine unevenness can be expected to further increase the current value of the CIGS solar cell.

Further, in order to obtain the CIGS solar cell of the present invention, the CIGS light absorbing layer is formed by sequentially depositing a layer ( α ) containing indium, gallium, and selenium, and containing copper and selenium on the substrate. The layer ( β ) is laminated in a solid phase state, and a layered body in which a layer ( α ) and a layer ( β ) are laminated is heated to grow crystals to form a first light absorbing layer composed of crystal grains having an average particle diameter A. And supplying indium, gallium, and selenium to the first light absorbing layer in a gas phase state, and simultaneously performing supply and crystal growth of indium, gallium, and selenium to form an average particle diameter of A/3 or less Since the first light absorbing layer and the second light absorbing layer can be continuously formed by the same apparatus only by changing the temperature conditions, the temperature can be improved and the cost can be reduced.

1‧‧‧Substrate

2‧‧‧ impurity diffusion prevention layer

3‧‧‧Back electrode layer

4‧‧‧CIGS light absorbing layer

4a‧‧‧1st light absorbing layer

4b‧‧‧2nd light absorbing layer

5‧‧‧buffer layer

5a‧‧‧1st buffer layer

5b‧‧‧2nd buffer layer

6‧‧‧Transparent electrode layer

Fig. 1 is a cross-sectional view schematically showing a CIGS solar cell according to an embodiment of the present invention.

Fig. 2(a) is a schematic view showing a secondary electron image obtained by observing a CIGS light absorbing layer (Example 1) of the CIGS solar cell of the present invention by SEM, and (b) is a schematic view showing the use of SEM observation. An illustration of a secondary electron image obtained from a CIGS light absorbing layer (Comparative Example 1) of a CIGS solar cell.

Form for implementing the invention

Next, the form for carrying out the invention will be described.

Fig. 1 is a cross-sectional view schematically showing a CIGS solar cell according to an embodiment of the present invention. The CIGS solar cell is sequentially laminated with a substrate 1, an impurity diffusion preventing layer 2, a back electrode layer 3, a CIGS light absorbing layer 4 composed of a first light absorbing layer 4a and a second light absorbing layer 4b, and a first buffer layer. The buffer layer 5 composed of the 5a and the second buffer layer 5b and the transparent electrode layer 6 can generate a current at the interface between the CIGS light absorbing layer 4 and the buffer layer 5 when the light is irradiated from the side of the transparent electrode layer 6. Hereinafter, the CIGS solar cell will be described in detail. In addition, in FIG. 1, each part is a schematic display, and is different from actual thickness, magnitude, etc. (FIG. 2 is also the same).

In other words, the CIGS solar cell uses a stainless steel foil (SUS) having a width of 10 mm, a length of 100 mm, and a thickness of 50 μm as the substrate 1, and an impurity diffusion preventing layer 2 having a thickness of 300 nm made of chromium (Cr) is provided on the substrate 1. On the impurity diffusion preventing layer 2, a back electrode layer 3 made of molybdenum (Mo) and having a thickness of 500 nm is provided. Further, on the back electrode layer 3, a first light absorbing layer 4a having a thickness of 2000 nm composed of crystal grains having an average particle diameter of 1000 nm and a second thickness 100 nm composed of minute crystal grains having an average particle diameter of 200 nm are sequentially provided. The light absorbing layer 4b is provided with a first buffer layer 5a made of CdS and having a thickness of 50 nm, and a second buffer layer 5b made of ZnO and having a thickness of 70 nm. Further, a transparent electrode layer 6 made of ITO and having a thickness of 200 nm is provided on the second buffer layer 5b.

When the CIGS solar cell having the above configuration is used, electrons can be taken out without losing electrons generated by the first light absorbing layer 4a composed of crystal grains having a large average particle diameter disposed on the substrate 1 side. And by being configured by The fine crystal grains having a small average particle diameter on the side of the punch layer 5 constitute the second light absorbing layer 4b, and a large amount of Na present in the crystal grain boundary can be supplied to the vicinity of the surface of the CIGS light absorbing layer 4 in a large amount. Therefore, the concentration of the receptor in the vicinity of the surface of the CIGS light absorbing layer 4 can be increased, and the conversion efficiency of the CIGS solar cell can be further improved. Further, since the second light absorbing layer 4b is formed thin on the surface side of the CIGS light absorbing layer 4, fine irregularities are formed on the surface of the CIGS light absorbing layer 4 (light incident surface), and the fine unevenness is formed by the fine unevenness The effect of the light on the inside can increase the current value of the CIGS solar cell.

The substrate 1 can be used in accordance with the purpose and design of the glass substrate, the metal substrate, the resin substrate, and the like in addition to the stainless steel foil (SUS). Examples of the glass substrate include a blue plate glass, a low alkali glass (high strain point glass) having a very low content of an alkali metal element, and an alkali-free glass containing no alkali metal element.

Further, when the CIGS solar cell is manufactured by a roll-to-roll method or a stepping roll method, the substrate 1 is preferably elongated and flexible. In addition, the term "long strip" means that the length in the longitudinal direction is 10 times or more the length in the width direction, and it is preferable to use 30 times or more.

Further, the thickness of the substrate 1 is preferably in the range of 30 μm or more and 200 μm or less, and preferably in the range of 50 μm or more and 100 μm or less. That is, since the thickness is too thick, the bendability of the CIGS solar cell disappears, and the stress becomes large when bent and there is a possibility of damage in the internal structure of the CIGS solar cell; on the contrary, when it is too thin, the CIGS is manufactured. In the case of a solar cell, the substrate 1 is longitudinally bent and it is observed that the defective rate of the CIGS solar cell tends to increase.

As a material for forming the impurity diffusion preventing layer 2 on the substrate 1, SiO ₂ , Al ₂ O ₃ , TiN, TiO ₂ , Ni, NiCr, Co, or the like can be used in addition to Cr. Further, in consideration of the balance between the effect and the cost, the thickness is preferably 50 nm or more and 1000 nm or less. Further, the impurity diffusion preventing layer 2 can be formed not on the substrate 1, but on the back electrode layer 3. Further, when the impurity originating from the substrate 1 is less likely to adversely affect the CIGS solar cell, the impurity diffusion preventing layer 2 may not be provided.

As a material for forming the back electrode layer 3 formed on the impurity diffusion preventing layer 2, in addition to molybdenum (Mo), W, Cr, Ti, or the like can be used. Further, the back electrode layer 3 may not be a single layer but a multiple layer. Further, the thickness (the total thickness of each layer in the case of a double layer) is preferably 50 nm or more and 1000 nm or less.

The CIGS light absorbing layer 4 formed on the back surface electrode layer 3 is the most characteristic of the present invention, and is formed on the first light absorbing layer 4a formed on the substrate 1 side and on the first light absorbing layer 4a. The second light absorbing layer 4b is composed of crystal grains having an average particle diameter A, and the second light absorbing layer 4b is made of minute crystal grains having an average particle diameter of A/3 or less. Composition. In other words, since the first light absorbing layer 4a formed on the substrate 1 side can secure electrons generated by the irradiation of light. At the same time, since the second light absorbing layer composed of minute crystal grains is provided on the surface side, a large amount of Na existing in the crystal grain boundary can be supplied to the vicinity of the surface of the CIGS light absorbing layer 4 in a large amount. It is possible to increase the concentration of the receptor in the vicinity. Further, fine irregularities are formed on the surface of the CIGS light absorbing layer 4 (the incident surface of the light). The effect of turning off the light by the fine concavities and convexities can be expected to increase the current value of the CIGS solar cell.

Further, since the electrons can be taken out without losing the generated electrons, the first light absorbing layer 4a is preferably composed of crystal grains having an average particle diameter of 1000 nm or more and 2000 nm or less. Further, the thickness thereof is preferably 1000 nm or more and 3,000 nm or less. When it is too thin, there is a tendency that the sunlight cannot be sufficiently absorbed. Conversely, when it is too thick, the cost increases due to an increase in material cost.

Further, the second light absorbing layer 4b is preferably composed of minute crystal grains having an average particle diameter of 50 nm or more and 300 nm or less. Since it is too small, there is a possibility that the electrons and the holes are recombined, and conversely, when it is too large, the tendency of Na to be insufficiently supplied at the crystal grain boundaries can be observed. Further, from the viewpoint of pn bonding, the thickness thereof is preferably 50 nm or more and 200 nm or less.

Each of the first light absorbing layer 4a and the second light absorbing layer 4b is formed of a compound crystal of a chalcopyrite type crystal structure composed of four elements of Cu, In, Ga, and Se. Further, the total thickness of the first light absorbing layer 4a and the second light absorbing layer 4b (thickness of the CIGS light absorbing layer 4) is preferably in the range of 1050 nm or more and 3200 nm or less, and is in the range of 1500 nm or more and 2500 nm or less. It is better. Since the thickness is too thin, the amount of light absorption is small and the performance of the CIGS solar cell is observed to be low. On the contrary, when it is too thick, the time required for forming the CIGS light absorbing layer 4 is increased and productivity can be observed. The tendency to change.

Further, the composition ratio of Cu, In, and Ga in the CIGS light absorbing layer 4 is preferably a formula satisfying 0.7 < Cu / (Ga + In) < 0.95 (mole ratio). When this formula is satisfied, it is possible to further prevent Cu( _2-x )Se from being excessively stored in the CIGS light absorbing layer 4, and the entire layer can be in a state in which Cu is slightly insufficient. Further, the ratio of Ga to In of the same element is preferably in the range of 0.10 < Ga / (Ga + In) < 0.60 (mole ratio).

The buffer layer 5 formed on the CIGS light absorbing layer 4 is composed of a first buffer layer 5a formed on the substrate 1 side and a second buffer layer 5b formed on the first buffer layer 5a. In addition to CdS and ZnO, ZnMgO, ZnO, Zn(OH) ₂ , In ₂ O ₃ , In ₂ S ₃ , Zn (O, S, OH) or the like of the mixed crystal can be used. Further, in the case of using the above-described n-type semiconductor or the like having a high resistance which is pn-bonded to the CIGS light absorbing layer 4, the buffer layer 5 may be provided as a single layer. Further, the thickness of each of the first buffer layer 5a and the second buffer layer 5b is preferably 30 nm or more and 200 nm or less. Further, when the buffer layer 5 is provided as a single layer, the thickness thereof is preferably 30 nm or more and 200 nm or less.

Since the transparent electrode layer 6 formed on the above-mentioned buffer layer 5 is located on the light incident side, it is preferable to use a material having a high transmittance of light as much as possible in order not to interfere with incident light. Examples of such a material include ITO, ZnO, In 2 O 3 , and SnO 2 . Further, in order to improve the conductivity or to adjust the band alignment, those materials containing a small amount of dopant materials can be suitably used. Examples of such a dopant material include Al:ZnO (AZO), B:ZnO (BZO), Ga:ZnO (GZO), Sn:In ₂ O ₃ (ITO), and F:SnO ₂ (FTO). Zn: In ₂ O ₃ , Ti: In ₂ Oe, Zr: In ₂ O ₃ , W: In ₂ O _{3 ,} or the like. From the viewpoint of light transmittance and conductivity, the thickness thereof is preferably 100 nm or more and 2000 nm or less.

Such a CIGS solar cell can be produced, for example, by the following method.

[Formation to the Back Electrode Layer 3]

The substrate 1 made of a long strip of SUS is prepared, and the substrate 1 is moved by a roll-to-roll method, and the impurity diffusion preventing layer 2 composed of Cr having a thickness of 300 nm is formed on the surface thereof by sputtering. The back electrode layer 3 composed of Mo having a thickness of 500 nm was formed by sputtering.

[Formation of CIGS Light Absorbing Layer 4]

On the back electrode layer 3, gallium selenide and indium selenide are sequentially laminated in a solid phase state while maintaining the substrate 1 at 420 ° C to form a layer ( α ) having indium, gallium, and selenium. . Further, in a state where the temperature of the substrate 1 is maintained at 420 ° C, copper selenide is laminated on the layer ( α ) to form a layer ( β ) having copper and selenium. On the substrate 1, a small amount of Se vapor is supplied to the laminate in which the impurity diffusion preventing layer 2, the back electrode layer 3, the layer ( α ), and the layer ( β ) are laminated, and the temperature of the substrate 1 is 650 ° C and This state is maintained for 15 minutes. Whereby the layers (beta]) becomes a liquid phase system, and the above-described copper-based layer (beta]) in the above diffusion layer ([alpha]) and the crystal growth. Then, while maintaining the temperature of the substrate 1 at 650 ° C, In, Ga, and Se are vapor-deposited while gradually increasing the vapor deposition amount of Ga while supplying a small amount of Se vapor. Thereby, the first light absorbing layer 4a having a crystal grain having an average particle diameter of 1000 nm and having a thickness of 2000 nm was formed on the back electrode layer 3.

Next, the temperature of the substrate 1 is cooled to 500 ° C, and the indium selenide and gallium selenide are simultaneously vapor-deposited on the first light absorbing layer 4 a to form The second light absorbing layer 4b having a crystal grain size of 200 nm and having a thickness of 100 nm. In other words, when In, Ga, and Se are supplied in a gas phase state and the supply and crystal growth are simultaneously performed, the new layer deposition seed crystal continuously flies before the crystal grows sufficiently, thereby hindering the growth of the crystal. Tiny crystal grains are suitable. Further, NaF is deposited on the second light absorbing layer 4b, and then Na is diffused to the first light absorbing layer 4a and the second light by setting the temperature of the substrate 1 to 420 ° C and holding it for 10 minutes in this state. The CIGS light absorbing layer 4 is formed by absorbing the crystal interface of the layer 4b.

[Formation of Buffer Layer 5]

The impurity diffusion preventing layer 2, the back electrode layer 3, and the CIGS light absorbing layer 4 were formed by the above-described roll-to-roll method, and the substrate 1 wound up in a roll shape was again unwound and cut into a cutting device, and all of them were cut into A predetermined length is obtained to obtain a laminate of a predetermined size (substrate 1 + impure diffusion preventing layer 2+ back electrode layer 3 + CIGS light absorbing layer 4). Then, a first buffer layer 5a (thickness: 50 nm) composed of CdS is formed on the CIGS light absorbing layer 4 (second light absorbing layer 4b) of the laminate by a solution growth method (CBD method), and by using In the sputtering method, a second buffer layer 5b (thickness: 70 nm) made of ZnO is formed on the first buffer layer 5a to form a buffer layer 5 composed of the first buffer layer 5a and the second buffer layer 5b.

[Step of Forming Transparent Electrode Layer 6]

A transparent electrode layer 6 (thickness: 200 nm) composed of ITO was formed on the buffer layer 5 (second buffer layer 5b) by sputtering. Further, an extraction electrode (not shown) such as a grid shape may be formed on the transparent electrode layer 6 by the same method as the back electrode layer 3. By doing so, the CIGS of the present invention can be obtained. Solar battery.

When this method is used, it is possible to continuously form the CIGS light absorbing layer 4 which is excellent in achieving high conversion efficiency by using a general-purpose vapor deposition apparatus under the conditions of changing the temperature, etc., and therefore, it is possible to improve the efficiency and cost of the production.

Further, in the above embodiment, the CIGS light absorbing layer 4 is formed by a roll-to-roller. However, each of the single sheets may be formed by adjusting the size of the substrate 1 or the like. Further, any of the impurity diffusion preventing layer 2 and the back electrode layer 3 is formed by a sputtering method, but the layers may be formed by a vapor deposition method, an inkjet method, a plating method, or the like.

Further, in the above embodiment, Na is added to the CIGS light absorbing layer 4 by using NaF, but it may be carried out using other Na compounds such as Na ₂ Se or Na ₂ S. Further, in the above-described embodiment, Na is added to the CIGS light absorbing layer 4 until the second light absorbing layer 4b is formed, and then vapor deposition is performed by means of vapor deposition of NaF, but it is also possible to form CIGS light absorption. Before the layer 4, the method of vapor-depositing NaF on the back electrode layer 3 is used.

Further, in the above-described embodiment, the first buffer layer 5a is formed by a solution growth method (CBD method), and the second buffer layer 5b is formed by a sputtering method. However, the layers may be formed by another method. Moreover, it can also be formed in any of a vacuum, an atmosphere, and an aqueous solution. Examples of the method to be carried out in a vacuum include a sputtering method, a molecular line epitaxing method, an electron beam evaporation method, a resistance heating vapor deposition method, a plasma CVD method, and an organic metal deposition method. Further, as a method of performing in an aqueous solution, a CBD can be cited. Method, plating method, etc.

Further, in the above-described embodiment, the transparent electrode layer 6 is formed by a sputtering method, but it may be formed by a vacuum deposition method, an organometallic vapor phase growth method, or the like.

Next, the embodiment will be described together with the comparative example. However, the present invention is not limited by this.

Example

[Example 1]

First, a substrate 1 of a stainless steel foil SUS430 (size: 10 × 100 mm, thickness: 50 μm) was prepared, and an impurity diffusion preventing layer 2 made of Cr having a thickness of 300 nm and a back electrode layer 3 having a thickness of 500 nm composed of Mo were laminated in this order. On it. Next, the substrate 1 to the back electrode layer 3 was placed in a vacuum vapor deposition apparatus, and gallium selenide (thickness: 400 nm) and indium selenide (thickness: 1000 nm) were sequentially placed while maintaining the substrate temperature at 420 °C. ) is laminated on the back electrode layer 3 to form a layer ( α ) having selenium, gallium, and indium. Next, copper selenide (thickness: 600 nm) was laminated on the above layer ( α ) while maintaining the substrate temperature at 420 ° C to form a layer (β) having copper and selenium. The layered body of the layer (α) and the layer (β) is laminated, and a small amount of Se vapor is supplied while heating, and the substrate temperature is maintained at 650 ° C for 15 minutes to crystallize, and second, a small amount of Se is supplied. The first light absorbing layer 4a having crystal grains having an average particle diameter of 1000 nm is formed by vapor-depositing In, Ga, and Se while gradually increasing the vapor deposition amount of Ga while maintaining the substrate temperature at 650 °C. (thickness 2000 nm).

Next, a laminate of the first light absorbing layer 4a is formed and In a state where the substrate temperature is 500° C., indium selenide and gallium selenide are simultaneously vapor-deposited on the first light absorbing layer 4 a, that is, the In, Ga, and Se are simultaneously supplied in a gas phase state. In the first light absorbing layer 4a, a second light absorbing layer 4b (thickness: 50 nm) having minute crystal grains having an average particle diameter of 200 nm is formed on the first light absorbing layer 4a. Then, the substrate temperature was maintained at 400 ° C, and the NaF was vacuum-deposited on the second light absorbing layer 4 b using a NaF vapor deposition source set at 750 ° C, and then heated by the substrate temperature of 420 ° C and The substrate temperature was maintained for 10 minutes, and Na was diffused to the grain boundaries of the first light absorbing layer 4a and the second light absorbing layer 4b to form the CIGS light absorbing layer 4. A secondary electron image obtained by observing the CIGS light absorbing layer 4 using SEM is schematically shown in Fig. 2(a).

Then, the first buffer layer 5a (thickness: 50 nm) composed of CdS, the second buffer layer 5b (thickness: 70 nm) made of ZnO, and the transparent electrode layer 6 (thickness: 200 nm) layer made of ITO are sequentially laminated. The target CIGS solar cell was fabricated by accumulating on the CIGS light absorbing layer 4 (second light absorbing layer 4b).

[Examples 2 to 9]

The same procedure as in Example 1 was carried out, except that the average particle diameter of the first light absorbing layer 4a, the thickness of the second light absorbing layer 4b, and the average particle diameter of the minute crystal grains of the structure were changed as shown in Table 1 below. Made of CIGS solar cells. Moreover, the particle size of the crystal grains constituting each of the light absorbing layers 4a and 4b can be any size, for example, by controlling the substrate temperature.

[Comparative Example 1]

The same as in the first embodiment except that the second light absorbing layer 4b is not formed. Made of CIGS solar cells. That is, the CIGS solar cell of Comparative Example 1 is a precursor product itself composed of crystal particles having a large particle diameter only by the CIGS light absorbing layer 4. The secondary electron image obtained by observing the CIGS light absorbing layer 4 using SEM is schematically shown in Fig. 2(b).

[Comparative Example 2]

A CIGS solar cell was produced in the same manner as in Example 1 except that the thickness of the second light absorbing layer 4b and the average particle diameter of the minute crystal grains of the structure were changed as shown in Table 1 below.

Each of the CIGS solar cells of the above-described Examples 1 to 9 and Comparative Examples 1 and 2 was produced in each of 10, and the conversion efficiency (%) and the average of the crystal grains constituting the first light absorbing layer 4a were measured according to the following procedure. The particle diameter and the thickness thereof, the average particle diameter of the minute crystal grains constituting the second light absorbing layer 4b, and the thickness thereof. These results are simultaneously shown in Table 1 which will be described later.

[conversion efficiency]

Each of the examples and comparative examples was irradiated with simulated sunlight (AM 1.5), and the conversion efficiency was measured using a solar simulator (manufactured by Yamashita Denso Co., Ltd., CELL TESTER YSS150). Further, the average of the respective values was calculated and set as the conversion efficiency (%) of each of the examples and the comparative examples.

[The average particle size]

The first and second light absorbing layers of the CIGS solar cells of Examples 1 to 9 and Comparative Examples 1 and 2 were used by a scanning electron microscope (manufactured by Hitachi HIGHTECHNOLOGIES Co., Ltd., S-3400N) (in the first comparative example, only the first light was used). The cross section of the absorption layer was enlarged to 20,000 times, and the crystal grain size in the vicinity of the center of each light absorbing layer was measured. Moreover, the average of the measured particle diameters is calculated and set as The average particle diameter of each light absorbing layer. Further, when the crystal is spherical, the particle diameter is measured by the diameter, and in the other shapes, the maximum length is measured.

[thickness]

The first and second light absorbing layers of the CIGS solar cells of Examples 1 to 9 and Comparative Examples 1 and 2 were obtained using a scanning electron microscope (manufactured by Hitachi HIGHTECHNOLOGIES Co., Ltd., S-3400N) (in Comparative Example 1, only the first one was used). The cross section of the light absorbing layer was observed to be 20,000 times enlarged, and the thickness of each light absorbing layer was measured. Further, the average of the measured thicknesses was calculated and set as the thickness of each light absorbing layer.

From the above results, it was found that Examples 1 to 9 showed high conversion values of 10.3% or more. In particular, the micro light absorbing layer 4b is formed The small crystal grains had an average particle diameter of 200 nm, and the thicknesses of the examples 1 to 4 in the range of 50 to 200 nm showed a very high conversion efficiency of 13.1 to 14.5%. On the other hand, in Comparative Example 1 in which the second light absorbing layer 4b was not formed, the conversion efficiency was 9.2%, and the average of the crystal grains constituting the first light absorbing layer 4a and the minute crystal grains constituting the second light absorbing layer 4b. Comparative Example 2 in which the difference in particle diameter was smaller than the predetermined range showed a lower conversion efficiency of 7.0%.

In the above embodiments, the specific embodiments of the present invention have been shown, but the above embodiments are merely illustrative and are not to be construed as limiting. The practitioner should clearly understand that a wide variety of variations are contemplated within the scope of the invention.

Industrial use possibility

Although the CIGS solar cell of the present invention is thin, but the conversion efficiency is very high, it is not only suitable for a large area, but also suitable for a space having a low load resistance or a space where a curved surface is required.

1‧‧‧Substrate

2‧‧‧ impurity diffusion prevention layer

3‧‧‧Back electrode layer

4‧‧‧CIGS light absorbing layer

4a‧‧‧1st light absorbing layer

4b‧‧‧2nd light absorbing layer

5‧‧‧buffer layer

5a‧‧‧1st buffer layer

5b‧‧‧2nd buffer layer

6‧‧‧Transparent electrode layer

Claims (4)

A CIGS solar cell comprising, in order, a substrate, a back electrode layer, a CIGS light absorbing layer, a buffer layer and a transparent electrode layer, wherein the CIGS light absorbing layer is formed by a first light absorbing layer formed on the substrate side, and The second light absorbing layer is formed on the first light absorbing layer, wherein the first light absorbing layer is composed of crystal grains having an average particle diameter A, and the second light absorbing layer is formed by an average particle diameter A/ 3 or less of fine crystal grains. The CIGS solar cell according to claim 1, wherein the average particle diameter of the crystal grains constituting the first light absorbing layer is 1000 nm or more and 2000 nm or less, and the average crystal grain size of the fine crystal grains constituting the second light absorbing layer is 50 nm or more. Below 300 nm. The CIGS solar cell according to claim 1 or 2, wherein the thickness of the second light absorbing layer is 50 nm or more and 200 nm or less. A method for manufacturing a CIGS solar cell, which is a method for manufacturing a CIGS solar cell having a substrate, a back electrode layer, a CIGS light absorbing layer, a buffer layer and a transparent electrode layer, wherein the CIGS light absorbing layer is a first light absorbing layer formed on the substrate side and a second light absorbing layer formed on the first light absorbing layer, wherein the first light absorbing layer is composed of crystal grains having an average particle diameter A, and The second light absorbing layer is composed of minute crystal grains having an average particle diameter of A/3 or less; and the manufacturing method is characterized in that the CIGS light absorbing layer is formed by the following steps: on the substrate, sequentially containing indium a layer of gallium and selenium ( α ), and a layer containing copper and selenium ( β ) are laminated in a solid phase state, and a layered body in which a layer ( α ) and a layer ( β ) are laminated is heated to form a crystal. a step of forming a first light absorbing layer composed of crystal grains having an average particle diameter A; and supplying indium, gallium, and selenium to the first light absorbing layer in a gas phase state by simultaneously performing indium, gallium, and selenium Supply and crystal growth to form micro-average particle size A/3 or less A second light absorbing layer composed of small crystal grains.