JP6099362B2 - Method for manufacturing silicon substrate laminate - Google Patents

Description

  The present invention relates to a silicon substrate laminate in which a conductive polymer layer in which graphene oxide is dispersed is laminated on a texture structure surface, and a method for manufacturing the same.

  2. Description of the Related Art In recent years, in order to achieve simplification of solar cell manufacturing processes, technological development for converting solar cell materials from silicon-based materials to organic materials has been actively conducted. However, solar cells using organic materials have problems such as low conversion efficiency and inferior durability compared to silicon solar cells because of the low conductivity of organic materials. It was.

  Therefore, in order to solve the problems of organic solar cells, organic-inorganic hybrid solar cells having both characteristics of high conversion efficiency of silicon raw materials and simple manufacturing processes of organic materials have been actively developed. . (For example, Patent Document 1)

  In general, in an organic-inorganic hybrid solar cell, a P-type organic conductive layer is formed on an N-type silicon substrate, and a PN junction is formed to function as a solar cell. Therefore, in order to obtain a solar cell with high photoelectric conversion efficiency, it has been a major technical problem to form an organic conductive layer having high conductivity uniformly on a silicon substrate.

  So far, a spin coating method is generally known as a method of forming an organic conductive layer on a silicon substrate. The spin coating method is a method of forming a thin film by centrifugal force by rotating a silicon substrate at a high speed. In particular, when forming a film on a silicon substrate having high smoothness, the rotation speed and the thin film to be formed are determined. Since the film thickness is proportional, it has been put to practical use in the semiconductor manufacturing process.

  Further, as a method of applying the organic conductive layer, a method of forming a thin film by atomizing a solution as a raw material of the organic conductive layer using ultrasonic waves is also known. (See Patent Document 2)

On the other hand, in recent years, in order to improve the performance of silicon-based solar cells, it is also known that the silicon substrate has a textured structure. By making the surface of the solar cell a textured structure, the surface by multiple reflection on the surface Reduced reflectivity (light that has been reflected once on the surface due to surface irregularities is incident again), and increased optical path length (because the irregularities make the light traveling direction oblique, resulting in a longer distance for the light to travel inside the silicon. Effect) is obtained.

In addition, as described above, the light travels obliquely inside the silicon, so when a part of the light is reflected by the back surface and reaches the surface again, the incident angle becomes greater than the critical angle, and all the light is within the silicon substrate. As a result, the performance of the silicon-based solar cell is improved.

Therefore, when it is going to improve the characteristic of an organic inorganic hybrid solar cell, the method of making the surface of a solar cell into a texture structure is simple.

Japanese Patent Laid-Open No. 10-321548 JP 2005-305233 A

  However, in order to improve the photoelectric conversion efficiency of the organic-inorganic hybrid solar cell, the present inventors tried to form an organic conductive layer on the silicon substrate surface on which the texture structure was formed by a spin coating method. An efficient solar cell could not be obtained.

  Moreover, even if the film-forming method described in Patent Document 2 is adopted, there is a problem that the photoelectric conversion efficiency of the solar cell is poor as in the spin coating method.

  The present invention has been made in view of such circumstances, and a conductive polymer layer in which graphene oxide is dispersed is laminated on a texture structure surface of a silicon substrate having a texture structure by an atomization film forming method. It is an object of the present invention to provide a silicon substrate laminate and to provide a manufacturing method thereof.

  By using the thus-produced silicon substrate laminate, an organic-inorganic hybrid solar cell with high photoelectric conversion efficiency can be provided.

The present invention aimed at solving such problems is as follows.
That is, the present invention is a silicon substrate laminate in which a conductive polymer layer in which graphene oxide is dispersed is laminated on a texture structure surface of a silicon substrate having a texture structure by an atomization film forming method.

The present invention also includes a step (1) of etching a silicon substrate with an alkaline solution to form a texture structure, and a conductive polymer layer in which graphene oxide is dispersed on the texture structure surface after the texture structure is formed. And a step (2) of laminating by a chemical film-forming method.

  ADVANTAGE OF THE INVENTION According to this invention, the silicon substrate laminated body by which the conductive polymer layer which disperse | distributed the graphene oxide on the silicon substrate which has a texture structure was laminated | stacked can be obtained. If an electrode pattern is formed using a metal such as silver on the obtained silicon substrate laminate, a solar cell having a photoelectric conversion efficiency of about 9% can be obtained.

  In addition, compared to the silicon solar cell manufacturing process, the P-type conductive layer can be created simply by firing the formed conductive polymer layer, which can reduce the cost of the manufacturing process. Become.

FIG. 1 is a schematic view of an atomization film forming apparatus used in the present invention. FIG. 2 is a scanning electron micrograph showing a cross section of the silicon substrate laminate of the present invention obtained in Example 1. 3 is an optical micrograph of a mixed solution of poly3,4-ethylenedioxythiophene, polystyrene sulfonate, and water in which graphene oxide is dispersed used in Example 1. FIG.

DESCRIPTION OF SYMBOLS 1 Conductive polymer solution in which graphene oxide is dispersed 2 Inner container 3 Outer container 4 Carrier gas 5 Fog 6 Communication pipe 7 Silicon substrate 8 Mesh electrode 9 Voltage generator 10 Ultrasonic generator

  Hereinafter, the present invention will be described in detail.

<Silicon substrate laminate>
The silicon substrate laminate of the present invention is formed by laminating a conductive polymer layer in which graphene oxide is dispersed on a texture structure surface.

  In the present invention, a known silicon substrate can be used without being limited by thickness or shape. Moreover, even if it is a P-type and an N-type silicon substrate, if a texture structure can be formed in the surface, it can be used as a silicon substrate in this invention. As described above, various silicon substrates can be used, but a single crystal silicon substrate having a (100) plane of the silicon substrate surface is preferable because a texture structure can be easily formed on the surface. When the surface of the single crystal silicon substrate having such a plane orientation is brought into contact with the alkali solution, the etching rate of the silicon substrate by the alkali solution is different between the (111) plane and the (100) plane, and therefore the (111) plane having a slow etching rate. Remains, and a good texture (pyramidal irregularities) is formed on the surface.

In the present invention, the texture structure formed on the surface of the silicon substrate only needs to have an uneven portion. In particular, the concavo-convex portion has a large number of pyramid structures, one of which has a height of 1 to 50 μm and preferably has a planar area of 1 to 1000 μm ² . If a texture structure having such an uneven portion is formed, the reflectance of light on the surface of the silicon substrate can be further lowered, and when a solar cell is manufactured, the photoelectric conversion efficiency can be improved. .

In the present invention, the graphene oxide dispersed in the conductive polymer layer is not particularly limited, and known graphene oxide can be used. For example, graphene oxide described in Japanese Patent No. 4527194 and graphene oxide produced by the modified Hummers method described in Journal of American Chemical Society Vol. 80 (1958), p. 1339 Can be used without any restrictions.

  Note that graphene oxide has a quadrilateral shape with a side of 0.5 to 10 μm at the stage of manufacturing by the above-described method. However, since it is very brittle, it is dispersed in a conductive polymer solution described later, and ultrasonic waves are generated. When it is applied, it becomes fine particles with a particle size of about 10 nm.

  In the present invention, the conductive polymer constituting the conductive polymer layer is not particularly limited as long as it is a known polymer having conductivity, but the mixture of polyethylene dioxythiophene and polysulfonate is water-soluble, And it is preferable from a viewpoint that electroconductivity is high. In particular, a mixture of poly 3,4-ethylenedioxythiophene and polystyrene sulfonate (hereinafter also referred to as PEDOT-PSS) is preferable.

The reason for this is that the valence band of Si and the highest occupied molecular orbital of PEDOT-PSS (High Occupied Molecular Orbital: difference between HOMO level and vacuum level and ionization potential) are almost equal to the valence band of silicon. Therefore, it is possible to improve the photoelectric conversion efficiency of the solar cell without forming a carrier energy barrier when contacting with silicon.

  The mixing ratio of polyethylene dioxythiophene and polysulfonate is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 2 parts by mass with respect to 1 part by mass of polyethylene dioxythiophene. preferable.

  The conductive polymer can be used by being dissolved in various solvents. Examples of the solvent include water, alcohol, acetone, and the like, but it is preferable to use water in order to make the dispersibility of the graphene oxide uniform. The concentration of the conductive polymer when dissolved in the solvent is only required to dissolve the conductive polymer, and is usually preferably in the range of 0.1 to 3% by mass. A solution of the conductive polymer is commercially available from Heraeus under the trade name “Clevios”.

Furthermore, since the graphene oxide produced by the above method is dispersed in the conductive polymer layer, electrons remaining from the covalent bond of ethylenedioxythiophene are conducted through the dispersed graphene oxide. Highest occupied molecular orbital (HOMO) -lowest unoccupied molecular orbital (LUMO) energy is increased, the internal electric field is enhanced at the interface with crystalline Si, and the silicon substrate laminate of the present invention In the case where a solar cell is manufactured using the above, an effect that the photoelectric conversion efficiency is improved can be obtained.

The ratio of the graphene oxide dispersed in the conductive polymer forming the conductive polymer layer is not particularly limited, but it is usually 5 to 20 parts by mass with respect to 1 part by mass of the conductive polymer. When the silicon substrate laminate is used as a solar cell, the release voltage is increased and the photoelectric conversion efficiency is improved.

In the present invention, the formation of the conductive polymer layer in which graphene oxide is dispersed uses an atomization film forming method. The use of the conventional spin coating method is not preferable because the photoelectric conversion efficiency when the obtained silicon substrate laminate is a solar cell is low.

In the atomization film forming method, a conductive polymer solution in which graphene oxide is dispersed is ultrasonically irradiated to atomize, and a voltage is applied to the generated mist to conduct conductivity in which graphene oxide is dispersed on a silicon substrate. This is a method for forming a conductive polymer layer. Details will be described later.

In the present invention, the thickness of the conductive polymer layer in which the graphene oxide is dispersed is not particularly limited, but is 5 to 500 nm from the viewpoint of film strength, uniformity, photoelectric conversion efficiency in the case of a solar cell, and the like. preferable.

The silicon substrate laminate of the present invention can be formed into an P-type organic conductive layer by forming electrodes thereon and firing at 50 to 180 ° C., and operates as a solar cell.

The solar cell manufactured in this way and excellent in photoelectric conversion efficiency can be used in a wide range of applications because the manufacturing cost can be reduced with the simplification of the manufacturing process.

On the other hand, when a conductive polymer layer is formed by a conventional technique such as spin coating to form a solar cell, the photoelectric conversion efficiency is lower than that of the present invention. As a cause of this, the present inventors, when the conductive polymer layer is formed on the silicon substrate having the texture structure by the conventional technique such as the spin coating method, the film of the conductive polymer layer. It is estimated that the photoelectric conversion efficiency of the solar cell is lowered due to the non-uniform thickness.

<Method for producing silicon substrate laminate>
Next, a method for producing the silicon substrate laminate of the present invention will be described.

Process (1)
First, the silicon substrate is etched with an alkaline solution to form a texture structure on the silicon substrate surface.
The alkali solution is preferably a mixture of an alkali metal salt and an alcohol in a ratio of 1: 1 to 5 (mass ratio). The alkali metal salt is preferably sodium hydroxide, and the alcohol is preferably isopropyl alcohol.

  As a method for bringing the silicon substrate into contact with the alkaline solution, for example, the silicon substrate may be immersed in a treatment tank into which the alkaline solution has been introduced. At this time, since the texture (uneven portion) is uniformly formed on the surface of the silicon substrate, the silicon substrate can be swung or vibrated in the treatment tank. Moreover, it can also be made to contact with a silicon substrate, stirring the alkaline solution in a processing tank, or performing circulation mixing.

Process (2)
Next, a conductive polymer layer in which graphene oxide is dispersed is laminated on the texture structure surface, but it is preferable to clean the surface on which the texture structure is formed before that. The cleaning method is not particularly limited, but the silicon substrate is placed in a dilute hydrofluoric acid aqueous solution, the oxide film on the surface of the silicon substrate is dissolved, and then organic substances and the like are removed with a mixed solution of ammonia and hydrogen peroxide. Remove and clean organic substances and heavy metals by dissolving the metals attached to the silicon substrate with a mixed solution of hydrochloric acid and hydrogen peroxide, and finally cleaning with ultrapure water (a method commonly called RCA treatment). Is preferred.

  After the above cleaning, a conductive polymer layer in which graphene oxide is dispersed is laminated on the texture structure surface by an atomization film forming method.

The atomization film-forming method (Chemical Mist Deposition, hereinafter also referred to as CMD method) is performed using, for example, the atomization film forming apparatus shown in FIG. An inner container 2 containing a conductive polymer solution (hereinafter also referred to as a raw material solution) 1 in which graphene oxide is dispersed is immersed in an outer container 3 filled with water, and an ultrasonic generator is added to the water in the outer container 3. The raw material solution 1 is atomized by irradiating ultrasonic waves at 10. A carrier gas 4 is caused to flow into the inner container 2, and the generated mist 5 is guided onto the silicon substrate 7 through the communication pipe 6. Further, a voltage is applied between the mesh electrode 8 provided on the communication pipe 6 above the silicon substrate 7 and the silicon substrate 7 by the voltage generator 9 to deposit a uniform conductive polymer layer on the silicon substrate 7.

By adopting the CMD method, a thin film can be formed on a substrate having irregularities on the surface, such as a silicon substrate on which a texture structure is formed. In the above atomization film-forming method, when a conductive polymer solution in which graphene oxide is dispersed is irradiated with ultrasonic waves, the graphene oxide becomes fine particles, and the graphene oxide is dispersed in the conductive polymer. It becomes foggy. Since the size of the mist affects the uniformity of the conductive polymer layer to be formed, it is preferable to irradiate ultrasonic waves of 2 to 5 MHz.

The carrier gas transports fog generated by ultrasonic waves onto a substrate on which a film is formed. The carrier gas is not particularly limited as long as it is inert, but nitrogen is preferable because it is easy to handle. The flow rate of the carrier gas is not particularly limited, but a flow rate of 5 to 1000 sccm (flow rate per minute in the standard state) is preferably employed from the viewpoint that uniform film formation is possible on the substrate. However, the flow rate of the carrier gas is greatly affected by the diameter of the communication pipe that supplies the mist, the diameter of the substrate on which the film is formed, the device configuration of the atomization film forming apparatus, etc. May be adjusted accordingly.

  In the present invention, a voltage is applied between the mesh electrode installed in the communication pipe above the silicon substrate and the silicon substrate. The voltage is preferably selected from a range of ± 1 to 10 kV because it is possible to control the flow of fog generated by ultrasonic waves to form a uniform film.

  In the present invention, the film formation time depends on the desired thickness of the conductive polymer layer, but when a conductive polymer layer having a thickness of 5 to 500 nm is formed, 10 minutes to 20 hours may be employed. preferable.

  Further, the substrate temperature during film formation is preferably 20 to 80 ° C. in order to rectify the flow of the mist that reaches the silicon substrate from the communication pipe that supplies the mist, thereby enabling uniform film formation.

  In the present invention, an electrode is formed on the silicon substrate laminate after the step (2). The metal of the electrode is preferable because aluminum or silver exhibits ohmic characteristics. Further, the shape of the electrode is preferably a comb shape or an antenna type for the reason of current collection. The method for forming the metal used for the electrode on the silicon substrate laminate is not particularly limited, but it is possible to employ a vapor deposition method or a printing method from the viewpoint of easy process and easy formation of the electrode pattern. preferable. After electrode formation, drying may be performed as necessary.

  Thereafter, the conductive polymer layer can be converted into a P-type organic conductive layer by baking at 50 to 180 ° C. When the firing temperature is less than 50 ° C., it is not preferable because the solvent remaining in the conductive polymer layer cannot be removed and the organic conductive layer does not function as a P-type semiconductor. When the firing temperature is higher than 180 ° C., the deterioration of the organic material constituting the organic conductive layer is not preferable.

  Thus, it can be set as the solar cell excellent in photoelectric conversion efficiency.

  The present invention is not limited to the above-described embodiment, and can be implemented with appropriate modifications within the scope not departing from the gist of the present invention.

  Below, the evaluation method of a silicon substrate laminated body and a solar cell was shown.

(Thickness of conductive polymer layer on silicon substrate laminate)
The thickness of the conductive polymer layer was measured by observing a cross section of the boundary between the conductive polymer layer portion and the silicon portion using a scanning electron microscope SU-8030 manufactured by Hitachi, Ltd. A typical observation example is shown in FIG. The thickness of the conductive polymer layer in FIG. 2 is 100 nm.

(Identification of conductive polymer layer on silicon substrate laminate)
Elemental analysis of the conductive polymer layer formed on the silicon substrate laminate was performed using an energy dispersive X-ray analyzer X-Max manufactured by HORIBA, Ltd. Moreover, the compound was identified by measuring the bond energy between the atoms which comprise a conductive polymer layer using Shimadzu X-ray photoelectron spectroscopy analyzer AXIS-HSi.

(Calculation method of photovoltaic cell photoelectric conversion efficiency)
The photoelectric conversion efficiency was calculated from the current-voltage characteristics obtained when white light having an air mass of 1.5 and an intensity of 100 mW / cm ² was irradiated.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these Examples.

Example 1
A test piece cut to a size of about 4 cm ² from a single crystal silicon substrate (φ4 inch) having a plane orientation (100) and a resistivity of 1-5 Ω · cm was prepared, and sodium hydroxide and isopropyl alcohol were added 1: 2 ( A texture structure was formed by immersing in a mixed solution mixed at a mass ratio of 40 minutes. Thereafter, cleaning with an organic solvent and RCA cleaning were performed, and this test piece was set on the sample stage of the atomization film forming apparatus.

Next, graphene oxide was prepared according to the method described in Journal of American Chemical Society Volume 80 (1958), page 1339. The shape of graphene oxide was flaky, and it was confirmed that the length of one side was about 0.5 to 10 μm.

  Next, graphene oxide powder is added to 100 parts by mass of a mixed solution of poly 3.4-ethylenedioxythiophene 0.5% by mass, polystyrene sulfonate 0.8% by mass, and the balance being water (Clevios 1000 manufactured by Heraeus). A raw material solution was prepared by dispersing at a rate of 12 parts by mass. The dispersion of the obtained raw material solution was confirmed with an optical microscope. The results are shown in FIG. From FIG. 3, it was confirmed that the graphene oxide was uniformly dispersed in the aqueous solution of PEDOT-PSS.

  The raw material solution is injected into the atomization film forming apparatus, the distance from the mesh electrode to the sample piece is 10 cm, the temperature of the silicon substrate is 40 ° C., the nitrogen flow rate is 60 sccm, the mesh electrode applied voltage is −5 kV, and the ultrasonic frequency is The atomization film forming apparatus was operated for 30 minutes at 3 MHz.

  A conductive polymer layer in which graphene oxide was dispersed in PEDOT-PSS was formed over a single crystal silicon substrate on which a texture structure was formed. The thickness of the PEDOT-PSS film formed under these conditions was 100 nm as a result of measurement with an electron microscope (see FIG. 1). In addition, with an energy dispersive X-ray analyzer, it can be confirmed that the main elements are mainly carbon, oxygen, and sulfur, and from the interatomic bond energy measured by the X-ray photoelectron spectrometer, a single crystal silicon substrate The thin film formed on top was evaluated as PEDOT-PSS.

  Next, a mouth-shaped silver electrode was formed on the PEDOT-PSS film by a printing method, and the silver electrode was dried at 100 ° C. for 5 minutes. Finally, it was baked in air at 140 ° C. for 30 minutes to complete the solar cell.

  The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 9.2%.

(Example 2)
In Example 1, a solar cell is formed under the same conditions as in Example 1 except that the thickness of the graphene oxide-dispersed conductive polymer film formed on the textured single crystal silicon substrate is 50 nm. did.

  The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 8.9%.

(Example 3)
In Example 1, a solar cell was formed under the same conditions as in Example 1 except that the thickness of the graphene oxide-dispersed conductive polymer film formed on the textured single crystal silicon substrate was 300 nm. did.

The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 8.8%.

Example 4
In Example 1, a solar cell was formed under the same conditions as in Example 1 except that after the electrode was prepared, the sample was baked in air at 170 ° C. for 30 minutes.

  The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 8.3%.

(Example 5)
In Example 1, a solar cell was formed under the same conditions as in Example 1 except that after the electrode was fabricated, the sample was baked in air at 70 ° C. for 30 minutes.

  The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 8.0%.

(Comparative Example 1)
In Example 1, a solar cell was formed in the same manner as in Example 1 except that a graphene oxide-dispersed conductive polymer film was formed on a textured single crystal silicon substrate by spin coating. did.

  The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 7.0%.

(Comparative Example 2)
In Example 1, a solar cell was formed in the same manner as in Example 1 except that a graphene oxide-dispersed conductive polymer film was formed on a single crystal silicon substrate having a flat surface.

  The produced solar cell was set in a photoelectric conversion efficiency measuring device, and the conversion efficiency was measured. As a result, the conversion efficiency was 5.4%.

Claims (2)

Etching the silicon substrate with an alkaline solution to form a texture structure (1);
After forming the texture structure, a step (2) of laminating a conductive polymer layer in which graphene oxide is dispersed on the texture structure surface by an atomization film forming method;
I have a,
In the atomization film forming method, an ultrasonic wave of 2 to 5 MHz is irradiated . A method for manufacturing a silicon substrate laminate. An electrode is formed on the silicon substrate laminate obtained by the method according to claim 1 , and then fired at 50 to 180 ° C. to produce a solar cell having a conductive polymer layer as a P-type organic conductive layer. Method.