JP5687367B2 - Compound particle, method for producing compound particle, method for producing semiconductor layer, and method for producing photoelectric conversion device - Google Patents

Description

  The present invention relates to compound particles for producing a semiconductor layer containing a group I-III-VI compound and a method for producing the same, as well as a method for producing a semiconductor layer and a method for producing a photoelectric conversion layer.

  Some solar cells use a photoelectric conversion device including a semiconductor layer containing a chalcopyrite-based I-III-VI group compound. Examples of the I-III-VI group compound include CIS and CIGS.

  As a method for producing such a semiconductor layer, Japanese Patent Application Laid-Open No. 2008-192542 discloses that a coating layer is formed using a solution containing fine particles of an I-III-VI group compound, and the semiconductor layer is formed by sintering the coating layer. It is described to form.

  In recent years, the demand for photoelectric conversion devices has been increasing, and further improvement in photoelectric conversion efficiency of the photoelectric conversion devices is desired.

  The objective of this invention is improving the photoelectric conversion efficiency of a semiconductor layer and a photoelectric conversion apparatus using the same.

  A compound particle according to an embodiment of the present invention is a compound particle containing a group IB element, an indium element, a gallium element, and a chalcogen element, and the atoms of the gallium element with respect to the total atomic concentration of the indium element and the gallium element The concentration ratio is higher at the surface than at the center.

  In the method for producing compound particles according to an embodiment of the present invention, a raw material liquid containing a group IB element, an indium element, and a chalcogen element is heated while being in contact with the gallium metal, whereby the indium element and the gallium element are heated. Forming a compound particle in which the ratio of the atomic concentration of the gallium element to the total atomic concentration is higher in the surface portion than in the central portion.

  A method for producing a semiconductor layer according to an embodiment of the present invention includes a step of forming a film using the above compound particles, and a step of forming a semiconductor layer containing the I-III-VI group compound by heating the film. It comprises.

  A method for manufacturing a photoelectric conversion device according to an embodiment of the present invention includes a step of forming a first semiconductor layer containing an I-III-VI group compound using the above-described method for manufacturing a semiconductor layer, Forming a second semiconductor layer having a conductivity type different from that of the first semiconductor layer so as to be electrically connected to the semiconductor layer.

  ADVANTAGE OF THE INVENTION According to this invention, the photoelectric conversion efficiency of a semiconductor layer and a photoelectric conversion apparatus can be improved.

It is a perspective view which shows an example of a photoelectric conversion apparatus. It is sectional drawing of the photoelectric conversion apparatus of FIG. It is a TEM photograph of the section of compound particles. It is a graph which shows the content ratio of Ga element in a compound particle. It is a graph which shows the content rate of In element in a compound particle.

  Hereinafter, compound particles, a method for producing compound particles, a method for producing a semiconductor layer, and a method for producing a photoelectric conversion device according to an embodiment of the present invention will be described in detail with reference to the drawings.

<(1) Compound particles>
The compound particles are used as a raw material for forming a semiconductor layer containing a I-III-VI group compound. The compound particles are formed into a film shape, and when heated, the compound particles react with each other to form a semiconductor layer.

An I-III-VI group compound is a group consisting of a group I-B element (also referred to as group 11 element), a group III-B element (also referred to as group 13 element), and a group VI-B element (also referred to as group 16 element). It is a compound, for example, Cu (In, Ga) Se ₂ (also referred to as CIGS), Cu (In, Ga) (Se, S) ₂ (also referred to as CIGSS, etc.) Cu (In, Ga) Se ₂ refers to a compound mainly composed of Cu, In, Ga, and Se, and Cu (In, Ga) (Se, S) ₂ refers to Cu, In, Ga, Se, and S. A compound containing as a main component.

  The compound particles contain an IB group element, an indium (In) element, a gallium (Ga) element, and a chalcogen element. The chalcogen element refers to a sulfur (S) element, a selenium (Se) element, and a tellurium (Te) element among VI-B group elements. Further, the compound particle has a ratio of atomic concentration of Ga element to total atomic concentration of In element and Ga element (hereinafter, a ratio of atomic concentration of Ga element to total atomic concentration of In element and Ga element is referred to as Ga ratio). However, it is higher at the surface portion than at the center portion of the compound particles.

  With such a configuration, the reactivity between the compound particles is increased, and a semiconductor layer with high crystallinity is easily formed. As a result, the photoelectric conversion efficiency of the semiconductor layer is improved.

  From the viewpoint of enhancing the reactivity between the compound particles and facilitating the formation of a good semiconductor layer with little composition variation, the Ga ratio in the surface portion of the compound particles is 1.3 to 2 times the Ga ratio in the central portion. .5 times may be sufficient.

The atomic concentration measurement of Ga element and In element of compound particles can be performed, for example, by the following method. First, a plurality of compound particles are mixed with a thermosetting resin such as an epoxy resin or an acrylic resin. Next, this mixture is heated and thermally cured. And this thermosetting body is cut | disconnected and the cross section of a compound particle is specified by observing the cross section with a transmission electron microscope (TEM). Then, the atomic concentration of each element is measured by energy dispersive X-ray analysis (EDS) at each point on the cross section of the compound particle. The atomic concentration is the number of atoms (atoms · cm ⁻³ ) contained in a unit volume.

  From the viewpoint of further increasing the reactivity between the compound particles to form a semiconductor layer having higher crystallinity, the average particle size of the compound particles may be 10 nm to 200 nm. The average particle diameter of the compound particles can be measured using, for example, a scanning electron microscope (SEM). Specifically, compound particles are fixed on a sample stage with an adhesive tape or the like, and the appearance is observed with an SEM. Then, the average particle size may be obtained by measuring the particle size of the plurality of compound particles from the obtained SEM image.

<(2) Method for producing compound particles>
The above compound particles can be produced, for example, as follows. First, a raw material solution in which an IB group element such as Cu, an In element, and a chalcogen element are dissolved is prepared. Then, by heating the raw material liquid and Ga metal in contact with each other, compound particles having a Ga ratio higher in the surface portion than in the central portion are generated. Note that the raw material liquid and the Ga metal are in contact with each other means that the Ga metal is not dissolved in the raw material liquid and exists in a metal state. The Ga metal in contact with the raw material liquid may be a liquid metal.

  That is, the IB group element and the In element are easily dissolved in the raw material liquid, and the Ga element is hardly dissolved, so that the dissolved IB group element and the In element react with the chalcogen element relatively quickly, Thereafter, the dissolved Ga element gradually reacts with the chalcogen element. As a result, compound particles having a higher Ga ratio in the surface portion than in the central portion are generated.

  As the solvent for the raw material liquid, for example, an organic solvent such as aniline or pyridine can be used. The IB group element and In element contained in the raw material liquid are dissolved in the above solvent in the form of a complex, for example. Further, the chalcogen element contained in the raw material liquid is dissolved in the solvent in the state of, for example, a chalcogen element-containing organic compound. The chalcogen element-containing organic compound is an organic compound containing a chalcogen element and is an organic compound having a covalent bond between a carbon element and a chalcogen element. Examples of the chalcogen element-containing organic compound include thiol, sulfide, disulfide, selenol, selenide, diselenide, tellurol, telluride, and ditelluride. From the viewpoint of further enhancing the chalcogenation reaction, the group IB element contained in the raw material liquid may be a complex in which a chalcogen element-containing organic compound is bound as a ligand. Similarly, the In element may be a complex in which a chalcogen element-containing organic compound is bound as a ligand. When a chalcogen element-containing organic compound is bonded to such a metal element as a ligand, the metal element and the chalcogen element are brought into a close state, and the reactivity becomes high.

  In a state where the raw material liquid and the Ga metal are in contact with each other, for example, by heating at 150 to 250 ° C., the Ga metal is gradually dissolved while forming a Ga complex by binding to a ligand in the raw material liquid. To do. Then, the dissolved Ga complex reacts with other metal elements and chalcogen elements in the raw material solution, and compound particles containing an IB group element, an In element, a Ga element, and a chalcogen element are generated. The ligand forming such a Ga complex may be one in which the ligand bonded to the IB group element or In element is liberated from the IB group element or In element, It may be added separately to the raw material liquid. From the viewpoint of appropriately increasing the chalcogenization reaction of Ga element, a chalcogen element-containing organic compound may be added to the raw material liquid as a ligand for forming the Ga complex.

  In the state where the raw material liquid and the Ga metal are in contact with each other, when the mixture of the raw material liquid and the Ga metal is heated, by changing the temperature increase rate of the mixture, The difference between the Ga ratio and the Ga ratio in the surface portion can be changed. That is, the lower the temperature increase rate of the mixture, the smaller the Ga ratio in the central part of the compound particles, and the larger the Ga ratio difference between the central part and the surface part tends to be.

  As described above, compound particles having a Ga ratio higher in the surface portion than in the central portion are generated in the raw material liquid. The compound particles may be removed by centrifugation or the like and washed. Thereby, impurities can be removed satisfactorily.

  Note that the raw material solution in which the IB group element and the In element are dissolved can be prepared by dissolving the IB group element complex and the In element complex in a solvent, but is not limited thereto. For example, a solution in which a ligand such as a chalcogen element-containing organic compound is dissolved in a solvent is prepared, and a Group IB metal and an In metal are added to the solution and heated. The raw material solution may be prepared by dissolving it as a complex compound.

<(3) Manufacturing method of semiconductor layer>
A method for producing a semiconductor layer using the compound particles will be described in detail below. First, a film is formed using the compound particles. As a method for forming a film, compound particles are mixed with a solvent or an additive (such as an additive such as a surfactant or a binder) to form a liquid, and this liquid is spin coater, screen printing, dipping, There is a method of forming a film with a spray or a die coater. As other methods, there are a method of forming a film by spraying powdery compound particles on a support together with a gas, and a method of forming a film by press molding powdery compound particles.

  Next, this film is heated to form a semiconductor layer containing an I-III-VI group compound. The coating is heated in an inert gas atmosphere such as nitrogen gas or a reducing gas atmosphere such as hydrogen gas at a temperature of 350 to 600 ° C., for example. Thereby, compound particles react with each other to generate a semiconductor layer having a polycrystalline structure. From the viewpoint of further promoting crystallization, a chalcogen element may be included in the atmosphere during heating of the film, for example, as sulfur vapor, hydrogen sulfide, selenium vapor, hydrogen selenide, tellurium vapor, or hydrogen telluride.

<(4) Configuration of photoelectric conversion device>
A photoelectric conversion device including a semiconductor layer produced using the compound particles will be described in detail below. FIG. 1 is a perspective view illustrating a photoelectric conversion device, and FIG. 2 is a cross-sectional view of the photoelectric conversion device. In the photoelectric conversion device 11, a plurality of photoelectric conversion cells 10 are arranged on the substrate 1 and are electrically connected to each other. In FIG. 1, only two photoelectric conversion cells 10 are shown for convenience of illustration. However, in an actual photoelectric conversion device 11, a large number of photoelectric conversion cells are arranged in the horizontal direction of the drawing or in a direction perpendicular thereto. The cells 10 may be arranged in a plane (two-dimensionally).

  1 and 2, a plurality of lower electrode layers 2 are arranged in a plane on a substrate 1. 1 and 2, the plurality of lower electrode layers 2 include lower electrode layers 2 a to 2 c that are arranged at intervals in one direction. A first semiconductor layer 3 is provided from the lower electrode layer 2a through the substrate 1 to the lower electrode layer 2b. In addition, a second semiconductor layer 4 having a conductivity type different from that of the first semiconductor layer 3 is provided on the first semiconductor layer 3. Furthermore, on the lower electrode layer 2 b, the connection conductor 7 is provided along the surface (side surface) of the first semiconductor layer 3 or through the first semiconductor layer 3. The connection conductor 7 electrically connects the second semiconductor layer 4 and the lower electrode layer 2b. The lower electrode layer 2, the first semiconductor layer 3, and the second semiconductor layer 4 constitute one photoelectric conversion cell 10, and adjacent photoelectric conversion cells 10 are connected in series via the connection conductor 7. Thus, the photoelectric conversion device 11 with high output is obtained. In addition, although the photoelectric conversion apparatus 11 in this embodiment assumes what enters light from the 2nd semiconductor layer 4 side, it is not limited to this, Light enters from the board | substrate 1 side. There may be.

  The substrate 1 is for supporting the photoelectric conversion cell 10. Examples of the material used for the substrate 1 include glass, ceramics, resin, and metal. As the substrate 1, for example, blue plate glass (soda lime glass) having a thickness of about 1 to 3 mm can be used.

  The lower electrode layer 2 (lower electrode layers 2a, 2b and 2c) is a conductor such as Mo, Al, Ti or Au provided on the substrate 1. The lower electrode layer 2 is formed to a thickness of about 0.2 μm to 1 μm using a known thin film forming method such as sputtering or vapor deposition.

  The first semiconductor layer 3 is a semiconductor layer that functions as a light absorption layer, and has a thickness of, for example, about 1 μm to 3 μm. The first semiconductor layer 3 mainly contains an I-III-VI group compound and can be produced using the above compound particles.

  The second semiconductor layer 4 is a semiconductor layer having a conductivity type different from that of the first semiconductor layer 3. When the first semiconductor layer 3 and the second semiconductor layer 4 are electrically joined to each other, a photoelectric conversion layer from which charges can be favorably extracted is formed. For example, if the first semiconductor layer 3 is p-type, the second semiconductor layer 4 is n-type. The first semiconductor layer 3 may be n-type and the second semiconductor layer 4 may be p-type.

As the second semiconductor layer 4, for example, CdS, ZnS, ZnO, Zn (OH, S), In ₂ S ₃ , In ₂ Se ₃ , In (OH, S), (Zn, In) (Se, OH) are used. ), And (Zn, Mg) O. In this case, the second semiconductor layer 4 is formed with a thickness of 10 to 200 nm by, for example, a chemical bath deposition (CBD) method. Zn (OH, S) refers to a mixed crystal compound containing Zn as a hydroxide and sulfide. In (OH, S) refers to a mixed crystal compound containing In as a hydroxide and sulfide. (Zn, In) (Se, OH) refers to a mixed crystal compound containing Zn and In as selenides and hydroxides. (Zn, Mg) O refers to a compound containing Zn and Mg as oxides.

  As shown in FIGS. 1 and 2, an upper electrode layer 5 may be further provided on the second semiconductor layer 4. The upper electrode layer 5 is a layer having a lower resistivity than the second semiconductor layer 4, and it is possible to take out charges generated in the first semiconductor layer 3 and the second semiconductor layer 4 satisfactorily. From the viewpoint of further increasing the photoelectric conversion efficiency, the resistivity of the upper electrode layer 5 may be less than 1 Ω · cm and the sheet resistance may be 50 Ω / □ or less.

  The upper electrode layer 5 is a 0.05 to 3 μm transparent conductive film such as ITO or ZnO. In order to improve translucency and conductivity, the upper electrode layer 5 may be composed of a semiconductor having the same conductivity type as the second semiconductor layer 4. The upper electrode layer 5 can be formed by sputtering, vapor deposition, chemical vapor deposition (CVD), or the like.

  Further, as shown in FIGS. 1 and 2, a collecting electrode 8 may be further formed on the upper electrode layer 5. The current collecting electrode 8 is for taking out charges generated in the first semiconductor layer 3 and the second semiconductor layer 4 more satisfactorily. For example, as shown in FIG. 1, the collector electrode 8 is formed in a linear shape from one end of the photoelectric conversion cell 10 to the connection conductor 7. As a result, the current generated in the first semiconductor layer 3 and the fourth semiconductor layer 4 is collected to the current collecting electrode 8 via the upper electrode layer 5, and to the adjacent photoelectric conversion cell 10 via the connection conductor 7. It is energized well.

  The collector electrode 8 may have a width of 50 to 400 μm from the viewpoint of increasing the light transmittance to the first semiconductor layer 3 and having good conductivity. The current collecting electrode 8 may have a plurality of branched portions.

  The collector electrode 8 is formed, for example, by printing a metal paste in which a metal powder such as Ag is dispersed in a resin binder or the like in a pattern and curing it.

  1 and 2, the connection conductor 7 is a conductor provided in a groove that penetrates the first semiconductor layer 3, the second semiconductor layer 4, and the upper electrode layer 5. The connection conductor 7 can be made of metal, conductive paste, or the like. In FIG. 1 and FIG. 2, the collector electrode 8 is extended to form the connection conductor 7, but the present invention is not limited to this. For example, the upper electrode layer 5 may be stretched.

<(5) Method for Manufacturing Photoelectric Conversion Device>
Next, a method for manufacturing the photoelectric conversion device 11 having the above configuration will be described. First, the lower electrode layer 2 made of Mo or the like is formed in a desired pattern on the main surface of the substrate 1 made of glass or the like using a sputtering method or the like.

  Then, the first semiconductor layer 3 is formed on the lower electrode layer 2 by using the semiconductor layer manufacturing method described above.

  After forming the first semiconductor layer 3, the second semiconductor layer 4 and the upper electrode layer 5 are sequentially formed on the first semiconductor layer 3 by a CBD method, a sputtering method, or the like. Then, the first semiconductor layer 3, the second semiconductor layer 4, and the upper electrode layer 5 are processed by mechanical scribing or the like to form a groove for the connection conductor 7.

  Thereafter, on the upper electrode layer 5 and in the groove, for example, a conductive paste in which a metal powder such as Ag is dispersed in a resin binder or the like is printed in a pattern, and this is heated and cured to collect the collecting electrode 8 and the connecting conductor. 7 is formed.

  Finally, the first semiconductor layer 3 to the current collecting electrode 8 are removed by mechanical scribing at a position shifted from the connection conductor 7 and divided into a plurality of photoelectric conversion cells 10, as shown in FIGS. 1 and 2. The photoelectric conversion device 11 is completed.

  The compound particles were evaluated as follows. In this example, CIGS was used as the semiconductor layer.

<Preparation of compound particles>
First, 500 mmol of aniline and 250 mmol of diphenyl diselenide were mixed to prepare a mixed solvent. Next, 65 mmol of metal In and 100 mmol of metal Cu were mixed in this mixed solvent, and the raw material liquid was prepared by stirring at 70 ° C. to completely dissolve the metal In and the metal Cu. Next, 35 mmol of metal Ga was added to this raw material solution, and Cu, In, Ga, and Se in diphenyl diselenide were reacted while stirring at 190 ° C. to gradually dissolve the metal Ga. And by adding hexane to this raw material liquid, powdery compound particles (hereinafter also referred to as evaluation powder) were taken out.

  This evaluation powder was mixed with a thermosetting acrylic resin, and the acrylic resin was thermoset. The thermosetting acrylic resin was cut, and this cut portion was observed with a TEM to identify a portion where the cross section of the evaluation powder appeared. The result of this TEM observation is shown in FIG. And the EDS analysis was performed about five places ae of the cross section of the powder for evaluation shown in FIG. As a result, it was confirmed that the powder for evaluation contained Cu element, In element, Ga element and Se element. Moreover, it has confirmed that the Ga ratio and In ratio in each point of the cross section of the powder for evaluation were as shown in FIGS. 4 and 5 show the ratio of the atomic concentration of Ga element to the total atomic concentration of Ga element and In element, and the ratio of the atomic concentration of In to the total atomic concentration of Ga element and In element, respectively. From this result, it was found that the generated evaluation powder had a higher atomic concentration ratio of the gallium element in the surface portion than in the center portion of the particles.

  Separately, the evaluation powder was observed by SEM, and the average particle size of the evaluation powder was measured from the obtained SEM image. From this result, it was found that the average particle size of the evaluation powder was 100 nm.

  On the other hand, the compound particle as a comparative example was produced as follows. First, 500 mmol of aniline and 250 mmol of diphenyl diselenide were mixed to prepare a mixed solvent. Next, this mixed solvent was divided into three equal parts, and 65 mmol of metal In was mixed into the first mixed solvent and dissolved at 70 ° C. The second mixed solvent was mixed with 35 mmol of metal Ga and dissolved at 70 ° C. The third mixed solvent was mixed with 100 mmol of metal Cu and dissolved at 70 ° C. And each mixed solvent which melt | dissolved each of these metals was mixed, and it stirred at 190 degreeC, and made Se in Cu, In, Ga, and diphenyl diselenide react. Then, by adding hexane to this mixed solvent, powdered compound particles (hereinafter also referred to as comparative powder) for comparison were taken out.

  When this comparative powder was subjected to EDS analysis by TEM observation as in the above, it was confirmed that the comparative powder contained Cu element, In element, Ga element and Se element. The ratio of In and the ratio of In element were not different between the particle surface portion and the central portion. The average particle size of the comparative powder was 100 nm.

<Production of photoelectric conversion device>
The evaluation particles and the comparative particles prepared as described above were each dispersed in aniline to prepare a dispersion. Next, a coating film was formed on the lower electrode layer made of Mo of the soda lime glass substrate by using each of these dispersions by a doctor blade method. The coating film was formed by applying each dispersion on the lower electrode layer using nitrogen gas as a carrier gas in a glove box. After coating, the sample was dried for 5 minutes while being heated to 110 ° C. on a hot plate to form a film.

  After the film formation, the film was heat-treated in a hydrogen gas atmosphere. The heat treatment was performed by rapidly heating the film to 525 ° C. in 5 minutes and holding it at 525 ° C. for 1 hour, and then naturally cooling to obtain a first semiconductor layer having a thickness of 1.5 μm. From the X-ray diffraction result of the first semiconductor layer, it was confirmed that the obtained first semiconductor layer was CIGS when both the evaluation powder and the comparative powder were used.

  Thereafter, cadmium acetate and thiourea were dissolved in aqueous ammonia, and the sample was immersed therein to form a second semiconductor layer containing CdS having a thickness of 0.05 μm on each first semiconductor layer. Further, an Al-doped zinc oxide film (upper electrode layer 5) was formed on the second semiconductor layer by a sputtering method to produce a photoelectric conversion device.

  When the photoelectric conversion efficiency of the photoelectric conversion device was measured, the photoelectric conversion efficiency of the photoelectric conversion device manufactured using the comparative powder was 7.4%, whereas the photoelectric conversion device manufactured using the evaluation powder was used. It was found that the photoelectric conversion efficiency of the device was 11.5%, which was superior to that when the comparative powder was used.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention.

1: substrate 2, 2a, 2b, 2c: lower electrode layer 3: first semiconductor layer 4: second semiconductor layer 5: upper electrode layer 7: connection conductor 8: collecting electrode 10: photoelectric conversion cell 11: photoelectric Conversion device

Claims (5)

Compound particles containing a group IB element, an indium element, a gallium element, and a chalcogen element,
Compound particles in which the ratio of the atomic concentration of gallium element to the total atomic concentration of indium element and gallium element is higher in the surface portion than in the central portion.   The compound particles according to claim 1, wherein the average particle size is 10 to 200 nm.   The ratio of the atomic concentration of the gallium element to the total atomic concentration of the indium element and the gallium element is increased from the center by heating the raw material liquid containing the IB group element, the indium element and the chalcogen element while being in contact with the gallium metal. The manufacturing method of the compound particle which comprises the process of forming a high compound particle in a surface part. Forming a film using the compound particles according to claim 1 or 2,
And a step of heating the film to form a semiconductor layer containing a group I-III-VI compound. Forming a first semiconductor layer containing an I-III-VI group compound using the method for producing a semiconductor layer according to claim 4;
Forming a second semiconductor layer having a conductivity type different from that of the first semiconductor layer so as to be electrically connected to the first semiconductor layer.