JP2013052361A - Chemical bath deposition apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a buffer layer of a photoelectric conversion device having higher quality at lower costs.SOLUTION: A chemical bath deposition apparatus 1 includes: a reaction vessel 3 for containing a reaction solution 2 for chemical bath deposition to form a film on a deposition surface 10a of a substrate 10 for film deposition; a substrate holding section 20 for holding the substrate 10 for film deposition such that at least the deposition surface 10a contacts the reaction solution 2, the substrate holding section including a fixing surface 21a made of stainless steel on which a back side of the substrate 10 for film deposition is closely fixed; a heater 30 disposed at a rear side of the fixing surface 21a, the heater heating the substrate 10 for film deposition from the back side thereof; and a reaction solution temperature control unit 40 for controlling the temperature of the reaction solution 2 in the reaction vessel 3.

Description

  The present invention relates to a chemical bath deposition apparatus used for manufacturing a buffer layer of a photoelectric conversion element.

A photoelectric conversion element including a photoelectric conversion layer and an electrode connected to the photoelectric conversion layer is used for applications such as solar cells. Conventionally, in the case of solar cells, Si-based solar cells using bulk single crystal Si or polycrystalline Si, or thin-film amorphous Si have been mainstream, but research and development of Si-independent compound semiconductor solar cells has been made. ing. Known compound semiconductor solar cells include bulk systems such as GaAs systems and thin film systems such as CIS or CIGS systems composed of group Ib elements, group IIIb elements, and group VIb elements. CI (G) S is represented by the general formula _{Cu 1-z In 1-x} Ga x Se 2-y S y ( where, 0 ≦ x ≦ 1,0 ≦ y ≦ 2,0 ≦ z ≦ 1) When x = 0, it is a CIS system, and when x> 0, it is a CIGS system. In this specification, CIS and CIGS are collectively described as “CI (G) S”.

  In a conventional thin film photoelectric conversion element such as a CI (G) S system, a buffer layer (Cd system such as CdS) is generally provided between a photoelectric conversion layer and a translucent conductive layer (transparent electrode) formed thereon. Compounds, Zn compounds such as Zn (O, OH, S)). In such a system, the buffer layer is usually formed by a chemical bath deposition (CBD) method.

  Possible roles of the buffer layer include (1) prevention of recombination of photogenerated carriers, (2) band discontinuous matching, (3) lattice matching, and (4) coverage of surface irregularities of the photoelectric conversion layer. . In the CI (G) S system or the like, the surface unevenness of the photoelectric conversion layer is relatively large. In particular, in order to satisfy the condition (4) well, it is considered that the CBD method which is a liquid phase method is preferable.

In the CBD method, a method of forming a buffer layer on a photoelectric conversion layer by immersing a substrate having a photoelectric conversion layer on the surface in a reaction solution heated to a predetermined temperature is common.
On the other hand, in the CBD method, particles (colloids) are generated in the reaction liquid at the same time as the buffer layer is deposited on the photoelectric conversion layer, and the particles adhere to the film formation surface. Since it cannot be used, there is a problem that it is difficult to reduce the cost and mass productivity is low. Note that in the case where a photoelectric conversion element is formed using a buffer layer having particles attached to the film formation surface, the photoelectric conversion element may be deteriorated in performance.

  Patent Document 1 discloses a CdS generation method and apparatus designed for mass production. Specifically, the temperature of the substrate holder is set to a temperature at which CdS is generated on the substrate (for example, 60 ° C.), and the solution temperature is maintained at a temperature at which CdS generation reaction does not occur (40 ° C. or lower). A method of forming a film is proposed. Further, it is described that CdS does not occur in portions other than the substrate, and continuous film formation is possible.

  Patent Document 2 discloses a film forming method for realizing cost reduction by reducing the amount of material solution used. Specifically, an apparatus has been proposed in which a required amount of a solution is dropped onto the substrate surface and a holding unit that holds the substrate is heated. As a result, the amount of solution used can be reduced, the temperature distribution of the substrate can be controlled with high accuracy, and a process with excellent film thickness distribution and film quality distribution and reduced film formation speed can be provided. ing.

  Patent Document 3 proposes a method of heating a holding portion that holds a substrate without heating the reaction solution, and it is described that the generation of particles in the reaction solution can be suppressed.

Japanese Patent Laid-Open No. 7-240385 JP 2009-259938 A US Patent Application Publication 2011/0027938

  With the CBD method and apparatus described in Patent Documents 1 to 3, generation of particles in the reaction solution can be suppressed, so that the adhesion of particles to the film formation surface is reduced and the reaction solution is repeatedly used. It is possible to reduce the cost as possible, and to achieve mass production.

  Furthermore, in practical use, in order to obtain a photoelectric conversion element having a higher photoelectric conversion rate, an apparatus capable of forming a buffer layer with higher quality is required.

  The present invention has been made in view of the above circumstances, can reduce the cost by suppressing the generation of particles in the reaction solution, can be a practical chemical bath deposition that can realize a higher quality buffer layer The object is to provide an apparatus.

The chemical bath deposition apparatus of the present invention comprises a reaction tank for storing a reaction solution for depositing a film on the deposition surface of a deposition substrate,
A substrate holding unit for holding the film-forming substrate so that at least the film-forming surface is brought into contact with the reaction solution; and having a fixed surface made of stainless steel or titanium to which the back surface of the film-forming substrate is closely fixed.
A heater disposed on the back side of the fixed surface for heating the film-forming substrate from the back side of the film-forming substrate;
And a reaction temperature controller for controlling the temperature of the reaction solution in the reaction tank.

  The heater is preferably a planar heater provided over an area larger than an area of the fixed surface on which the film formation substrate is fixed.

  The heater is particularly preferably a rubber heater.

  The substrate holding part preferably holds the film-forming substrate so that the film-forming surface faces vertically downward (the direction facing the bottom surface of the reaction vessel). It is particularly preferable that the fixed surface is a convex curved surface.

  Or it is preferable that the said board | substrate holding | maintenance part hold | maintains the said film-forming substrate so that the said film-forming surface may incline from the perpendicular downward direction.

  Further, the substrate holding unit may hold the film-forming substrate in parallel to the side wall surface of the reaction vessel.

  It is preferable that the substrate holding portion includes an end surface protection member that prevents a side end surface of the substrate fixed to the fixing surface from coming into contact with the reaction solution.

  Furthermore, it is desirable that at least a portion of the inner wall of the reaction vessel that contacts the reaction solution is coated with a hydrophobic material.

  Since the chemical bath deposition apparatus of the present invention is individually provided with a heater for heating the film-forming substrate from the back surface and a reaction liquid temperature control unit for controlling the temperature of the reaction liquid, the temperature of the film-forming substrate and the reaction The temperature of the liquid can be individually controlled. It is possible to make the temperature of the reaction solution in the reaction tank more uniform by making the temperature of the substrate and the reaction solution the same, and by setting the substrate temperature higher than the reaction solution, particles (colloid in the reaction solution) ) Can be suppressed, and a film can be selectively formed on the substrate. Since the generation of particles (colloid) can be repeatedly used, the cost of the reaction liquid can be reduced.

  Since the fixed surface to which the film formation substrate is fixed is made of stainless steel or titanium, the heat from the substrate heating heater can be transmitted to the film formation substrate uniformly and with high thermal conductivity. The uniformity is very high. Therefore, the uniformity of the film thickness of the layer to be formed can be improved, and a buffer layer with higher quality than before can be obtained.

Sectional drawing which shows schematic structure of the chemical bath deposition apparatus which concerns on embodiment of this invention 1 is a perspective view of the chemical bath deposition apparatus shown in FIG. Cross-sectional schematic diagram showing a design change example of the substrate holder The schematic diagram which shows schematic structure of the CBD apparatus used for Example 4 The schematic diagram which shows schematic structure of the CBD apparatus used for the comparative example 1

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a chemical bath deposition apparatus 1 (hereinafter referred to as a CBD apparatus 1) according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a schematic configuration of the CBD apparatus 1 shown in FIG. It is.
As shown in FIG. 1, the CBD apparatus 1 holds a reaction tank 3 that stores a reaction solution 2 for depositing a film on a film formation surface 10 a of a film formation substrate 10 and a film formation substrate 10. A substrate holding unit (substrate holder) 20 that performs heating, a heater 30 that heats the deposition substrate 10 from the back side thereof, and a reaction liquid temperature control unit 40 that controls the temperature of the reaction liquid 2 in the reaction tank 3. ing.

  The substrate holder 20 includes a stainless steel plate-like member 21 having a fixing surface 21a to which the film forming substrate 10 is closely fixed, and a wall surface 22 provided continuously on the bottom surface of the plate-like member 21. A container-shaped holder main body 23 and a support portion 26 connected to the holder main body 23 and capable of being hooked on a part of the reaction vessel 3 are provided.

  Here, the fixed surface 21 a of the stainless plate member 21 is configured to be a curved surface that protrudes outward from the main body 23. As shown in FIG. 1, the fixing surface 21a is curved in a convex shape whose center in the left-right direction on the paper surface is closest to the bottom surface, and the film formation substrate 10 is curved and fixed along this curved surface. . The film-forming substrate 10 is held so that the film-forming surface faces downward in the vertical direction (axis A in FIG. 1) (the direction facing the bottom surface of the reaction vessel). At this time, since the film-forming substrate 10 is curved and fixed, the film-forming surface 10a is also curved, so that bubbles can be prevented from adhering to the film-forming surface 10a. During the film formation, bubbles (gas) are generated in the reaction chamber 3, but when these bubbles adhere to the film formation surface, the buffer layer does not precipitate in the part where the bubbles are attached, and complete film formation is achieved. It becomes difficult to do. That is, when the film formation substrate is held such that the film formation fixing surface is flat and the film formation surface is horizontal with respect to the reaction liquid surface 2a, that is, the flat film formation surface 10a is vertically downward. There is a possibility that a film deposition defect may occur due to adhesion to the film deposition surface. On the other hand, by curving the film formation surface 10a as in the present embodiment, the adhesion of bubbles can be suppressed, and better film formation can be realized. In this case, as the base substrate 11 of the film formation substrate 10, a substrate having flexibility enough to bend along the curve of the fixed surface may be used. The preferred curvature of the curved surface depends on the size of the reaction vessel, but is preferably in the range of 100 mm to 10000 mm when expressed by the radius of curvature.

  As a material for the stainless plate member, SUS316 (JIS standard) having alkali resistance is most preferable. The surface of stainless steel may be coated with a material having heat resistance and alkali resistance, such as Teflon (registered trademark) or a carbon-based material (carbon material such as carbon material or SiC).

  In the present embodiment, the substrate holder 20 has the film-forming substrate 10 on the fixed surface 21 a and the film-forming substrate 10 so that only the surface (film-forming surface) 10 a can contact the reaction liquid 2. It is configured to be held by the liquid leakage prevention jig 24 toward the substrate holder body 23. Further, the liquid leakage prevention jig 24 and the film formation substrate 10 are prevented from entering the reaction liquid 2 through the gap between the liquid leakage prevention jig 24 and the grasped film formation substrate 10 by the fixing frame 25 that can be fastened and fixed. Is configured to be fastened and fixed. The liquid leakage prevention jig 24 and the fixed frame 25 constitute an end face protection member that prevents the side end face of the substrate from coming into contact with the reaction liquid.

  As described above, only the film formation surface of the film formation substrate 10 can be brought into contact with the reaction liquid 2, so that portions other than the outermost layer 13 of the film formation substrate 10 do not come into contact with the reaction liquid 2. In the case where the film substrate 10 can be held, a base material that may be eroded by the reaction liquid 2, for example, an Al base material, can be used as the base substrate 11.

  The heater 30 is uniformly arranged in a region larger than the film-forming substrate 10 on the surface opposite to the fixed surface 21 a of the stainless plate member 21 of the holder body 23, that is, on the inner bottom surface of the container-shaped holder body 23. Sheet heater. In particular, a rubber heater is provided here. By providing the rubber heater in a region larger than the area of the film-forming substrate 10, the film-forming substrate 10 can be uniformly heated through the stainless plate member, and the uniformity of the substrate temperature can be improved. . The higher the uniformity of the substrate temperature, the higher the film thickness uniformity of the deposited film, which is preferable.

The reaction liquid temperature control unit 40 includes a temperature adjusting unit 41 provided on the bottom surface of the reaction tank 3 and a temperature measurement unit 42 that measures the reaction liquid temperature near the bottom surface. As the temperature adjustment means 41, a heating and / or cooling means is provided. Various heaters may be used as the heating means, and a heat sink may be provided as the cooling means in addition to a water cooling device using cold water or the like, an air cooling device such as a fan.
Note that the temperature of the reaction liquid is defined by the temperature of the reaction liquid in the vicinity where the temperature adjusting means 41 is provided.

  As the temperature adjusting means 41, it may be possible to provide a separate thermostat and circulate the reaction liquid to make the temperature of the reaction liquid constant. However, by circulating the reaction liquid, particles (colloid) in the reaction liquid may be used. Therefore, a structure in which the reaction solution is not circulated during film formation is more preferable.

  The CBD apparatus 1 includes a heater 30 for heating the film formation substrate 10 and a reaction liquid temperature control unit 40 for controlling the temperature of the reaction liquid. The temperature of the film formation substrate 10 and the reaction liquid Can be controlled individually. It is possible to increase the uniformity of the reaction solution temperature by making the temperature of the substrate and the reaction solution the same, or by changing the temperature of the substrate and the reaction solution, for example, the reaction temperature only in the vicinity of the substrate (around 70-90 ° C.) On the other hand, by reducing the temperature of the reaction solution near the reaction solution temperature control unit to be lower than the reaction temperature, the generation of particles (colloid) in the reaction solution is suppressed, and the film is selectively formed on the substrate. It is also possible to do so.

The inner wall of the reaction vessel 3 is preferably coated with a hydrophobic material having alkali resistance. By applying this hydrophobic material coating, film deposition on the inner wall during film deposition on the substrate can be suppressed. Thereby, waste of raw materials and labor of maintenance can be saved.
However, even if coating is performed with a hydrophobic material, deposits stick to the inner wall after a long film formation step. Such precipitates can be dissolved and removed by washing with an aqueous hydrochloric acid solution or the like. Therefore, it is preferable that the hydrophobic material for coating the inner wall has not only alkali resistance but also acid resistance. As such a coating material, Teflon (registered trademark) is suitable.

Since the fixing surface to which the film formation substrate 10 is fixed is made of stainless steel, heat from the heater 30 for heating the substrate can be transmitted to the substrate uniformly and with high thermal conductivity. It will be very expensive. Therefore, the uniformity of the film thickness of the deposited layer can be improved.
The same effect can be obtained even if the stainless steel plate member having the fixed surface is replaced with a member made of titanium.

(Design changes)
FIG. 3 is a schematic cross-sectional view showing a design change example 20 ′ of the substrate holder. In the CBD device 1 of the above-described embodiment, the substrate fixing surface 21a of the substrate holder 20 is a curved surface. However, as shown in FIG. 3, the stainless plate member 27 is not curved and the fixing surface 27a is flat. As an example, the film-forming substrate 10 may be held so that the film-forming surface 10a is inclined vertically downward (horizontal with respect to the reaction liquid surface 2a) (as indicated by a dotted line in FIG. 3). The tilt angle of the substrate is preferably in the range of 1 degree to 30 degrees. When the film formation surface of the substrate is inclined from the horizontal, it is possible to suppress bubbles from adhering to the photoelectric conversion semiconductor layer 13 as in the case where the film formation surface is curved.

  When the substrate fixing surface 21a is a curved surface, it is necessary that the base substrate 11 of the film forming substrate 10 is flexible. However, if the substrate fixing surface 21a is a flat fixing surface 27a, an inflexible material such as glass is used. It is also possible to use a substrate.

  The CBD apparatus includes a plurality of raw material solution tanks for storing various raw material solutions of the reaction liquid, a tank for mixing the raw material solutions, and a piping line for injecting the mixed reaction liquid into the reaction tank. It is preferable that it is provided. Moreover, it is preferable to provide a piping line for returning the solution to the reaction tank again after circulating the reaction liquid in the reaction tank and filtering the particles (colloid) generated in the reaction liquid. As described above, since the circulation of the reaction liquid promotes the generation of particles (colloid), it is preferably performed during the interval between film formations, not during film formation.

  You may provide the transmittance | permeability measurement part which measures the transmittance | permeability of a reaction liquid. In this case, the relationship between the decrease in transmittance and the film thickness is examined in advance, the transmittance of the reaction solution is measured in-situ, and the film formation is completed based on the decrease in transmittance. To be able to.

  You may provide the pH measurement part which measures pH of a reaction liquid. In this case, the relationship between the change in pH and the film thickness can be examined in advance, the pH of the reaction solution can be measured in situ, and film formation can be terminated based on the amount of change in pH.

  Or you may provide the electrical conductivity measurement part which measures the electrical conductivity of a reaction liquid. In this case, the relationship between the change in electrical conductivity and the film thickness is examined in advance, the electrical conductivity of the reaction solution is measured in situ, and the film formation is terminated based on the amount of change in electrical conductivity. Can be.

  In addition, you may use the change of the transmittance | permeability, pH, and electrical conductivity for the detection of the use limit of a reaction liquid. Moreover, you may make it use for the determination of not only the timing of replacement | exchange of a reaction liquid but the timing of adding a fresh reaction liquid or a recycle solution additionally.

  In the CBD device 1, it is preferable to use an alkali-resistant material, for example, SUS316, for the metal parts that may come into contact with the CBD liquid, including the substrate holder. The inner wall of the reaction vessel 3 is preferably coated with Teflon (registered trademark).

  In the CBD apparatus 1 shown in FIG. 1, when batch-type film formation is performed, if the substrate holder is configured to be rotatable and the substrate holder is rotated during the film formation, uneven deposition can be further suppressed. It is considered that the uniformity of the film can be further improved.

The CBD device 1 is disposed in a housing (not shown) from the viewpoint of dust contamination. At this time, it is preferable that an exhaust port for exhausting alkaline gas is provided in a part of the housing.
In addition, it is preferable that the case has an antistatic function from the viewpoint of preventing dust adhesion. The antistatic function may be provided by applying an antistatic agent to the casing, or may be provided by forming the casing from a resin material in which a conductive material is kneaded. May be.

  The CBD apparatus 1 shown in FIG. 1 is configured to attach a rectangular substrate to the substrate holder 20 one by one, assuming a form in which batch-type film formation is performed. However, the present invention is not limited to a batch type, and can be applied to a roll-to-roll type film formation. Any substrate holder may be used as long as it has a mechanism capable of sequentially mounting a region of the roll substrate. Specifically, instead of a stainless steel plate-like member having a fixed surface, a substrate holder having a stainless steel rotary drum-shaped holder body is used, and a drum surface is attached to a region of a long substrate with a fixed surface sequentially. And a heater is provided inside the drum.

  The CBD device of the present invention can be suitably used for forming a buffer layer of a photoelectric conversion element in which a lower electrode, a photoelectric conversion semiconductor layer, a buffer layer, and a transparent electrode are stacked on a substrate. Using the CBD device 1 of the embodiment shown in FIG. 1, a substrate in which a lower electrode and a photoelectric conversion semiconductor layer are formed on a substrate is used as a film formation substrate 10, and a buffer layer is formed on the photoelectric conversion semiconductor layer 13 that is the outermost surface. A method for forming a film will be briefly described.

The temperature of the reaction liquid 2 in the reaction tank 3 is set to a constant temperature (for example, 40 ° C.) by the reaction liquid temperature control unit 40.
On the other hand, the deposition substrate 10 is fixed to the fixing surface 21 a of the substrate holder 20 outside the reaction vessel 3. Thereafter, the heater 30 is turned on to heat the substrate 10. The heating temperature of the substrate 10 is set to 90 ° C., for example. Thereafter, the substrate 10 is immersed in the reaction solution 2 by the substrate holder 20.

A buffer layer is deposited on the photoelectric conversion semiconductor layer 13 by holding the substrate 10 for a certain period of time so that the substrate 10 faces the bottom surface of the reaction vessel 3 so that at least the film formation surface 10 a is in contact with the reaction solution 2.
The substrate 10 is maintained at a constant temperature (90 ° C.) by the heater 30 during the buffer layer deposition. On the other hand, the temperature of the reaction solution 2 is also maintained at a constant temperature (40 ° C.) by the reaction solution temperature controller 40. Although the reaction liquid has a temperature distribution in the solution, the temperature of the reaction liquid 2 is maintained so that at least the temperature in the vicinity of the reaction liquid temperature control unit 40 is a constant temperature as described above.

  The film formation time (reaction time) is not particularly limited. Although the film formation time depends on the substrate temperature and the reaction liquid temperature, for example, the base can be satisfactorily covered in 10 to 60 minutes, and a layer having a sufficient thickness as a buffer layer can be formed.

During the film formation, it is preferable that the reaction liquid is not stirred vigorously or not at all. Here, the stirring includes not only stirring by a stirrer or the like but also liquid circulation and application of ultrasonic waves to the reaction solution. Agitation of the reaction solution promotes the generation of particles (colloid) in the reaction solution and increases the amount of particles (colloid) floating in the reaction solution, so that the particulate solid adheres to the surface of the deposited film. The possibility of becomes high.
In the embodiment of Patent Document 1 described in the section of the prior art, it is described that the solution concentration is controlled to be constant by circulating the reaction solution. When such circulation is performed, the substrate, the reaction solution, The temperature difference provided between the two shifts in the direction of decreasing. On the other hand, if the stirring (liquid circulation) is not performed, the temperature difference can be further maintained, and the effect of selective deposition on the substrate is higher.

Here, the particulate solid is a solid in which particles having a primary particle size of the order of several tens to several hundreds of nm are aggregated. If a photoelectric conversion element is produced with particulate solids (secondary aggregates) with a circle-equivalent diameter of approximately 1 μm or more attached to the surface of the buffer layer, the resistance increases only in this part and a region where current does not flow easily occurs. Thus, the performance of the photoelectric conversion element may be deteriorated.
In addition, in the process of forming the light-transmitting conductive layer on the buffer layer, the particulate solid (secondary aggregate) attached to the buffer layer surface is peeled off, and at the same time, the buffer layer is peeled off, which causes photoelectric conversion. There is a possibility that the performance of the element is deteriorated.

  By forming the buffer layer without stirring the reaction solution, generation of particulate solid can be suppressed as compared with the case of stirring.

  After the buffer layer is formed, the substrate together with the substrate holder is pulled up from the reaction solution, and the substrate on which the buffer layer is formed on the photoelectric conversion semiconductor layer is removed from the substrate holder. At this time, before removing the substrate from the holder, a certain amount of water washing may be performed while the substrate remains attached to the holder. Finally, the substrate on which the buffer layer is formed is sufficiently washed with water after being removed from the holder, and further removed with a moisture removing mechanism such as an air knife after washing with water. Further, when the buffer layer is made of ZnS, Zn (S, O), Zn (S, O, OH), the temperature is 150 to 230 ° C., preferably 170 to 210 ° C. for 5 to 60 minutes. Annealing is performed. The annealing method is not particularly limited, but warm air heating using a commercially available oven, electric furnace, vacuum oven or the like is preferable. By performing the heat treatment in this manner, characteristics such as conversion efficiency of the photoelectric conversion element can be improved.

The “CBD method” is a general formula [M (L) _i ] ^{m +} Ｍ M ^{n +} + iL (wherein, M: metal element, L: ligand, m, n, i: each represents a positive number). By using a metal ion solution having a concentration and pH that are supersaturated by the equilibrium as expressed as a reaction solution and forming a complex of metal ions M, a metal compound thin film on the substrate at a moderate speed in a stable environment Is a method of precipitating.

The reaction solution used for manufacturing the buffer layer using the CBD device 1 contains a metal (M) source of Cd, Zn or In and a sulfur source. Thereby, a buffer layer such as CdS, ZnS, Zn (S, O) and / or Zn (S, O, OH), InS, In (S, O) and / or In (S, O, OH) is formed. can do. Use sulfur-containing compounds such as thiourea (CS (NH ₂ ) ₂ , thioacetamide (C ₂ H ₅ NS), thiolia, thiosemicarbazide, thiourethane, diethylamine, triethanolamine, etc. as the sulfur source Can do.

  The concentration of each component in the reaction solution is not particularly limited as long as a desired buffer layer can be deposited.

In the case of forming a CdS buffer layer, the above sulfur source, a Cd compound (for example, cadmium sulfate, cadmium acetate, cadmium nitrate, cadmium chloride and their hydrates), aqueous ammonia or ammonium salt (for example, CH ₃ COONH). ₄ , NH ₄ Cl, NH ₄ I and (NH ₄ ) ₂ SO ₄ or the like) can be used as the reaction solution.

In the case of forming a buffer layer made of a Zn compound layer of Cd-free such as ZnS, Zn (S, O), Zn (S, O, OH), the above sulfur source and a Zn compound (for example, zinc sulfate, zinc acetate) , Zinc nitrate, zinc chloride, zinc carbonate, and their hydrates) and a Cd-free mixed solution of aqueous ammonia or ammonium salt (same as above) can be used as the reaction solution.
In addition, when forming the buffer layer which consists of Zn compound layers, it is preferable to make a reaction liquid contain a citric acid compound (trisodium citrate and / or its hydrate). By containing a citric acid compound, a complex is easily formed, crystal growth by the CBD reaction is well controlled, and a film can be stably formed.

  As shown in the CBD device 1 of the embodiment, when the substrate fixing surface 21a of the substrate holder 20 is curved, it is suitable for forming a buffer layer on a flexible substrate. On the other hand, when the fixed surface 27a of the substrate holder 20 'is a flat surface as in the design modification example shown in FIG. 3, it can be applied regardless of the flexibility or inflexibility of the substrate.

The film formation substrate 10 includes at least a base substrate 11, a lower electrode (not shown) formed thereon, and a photoelectric conversion semiconductor layer 13 constituting the outermost surface.
Specific examples of the base substrate 11 include a glass substrate, a metal substrate such as stainless steel having an insulating film formed on the surface thereof, and a resin substrate such as polyimide.

  In addition, when the substrate holder 20 includes the end face protection member as in the CBD device 1 of the present embodiment, the substrate 11 may include a component that dissolves in the CBD reaction solution. Therefore, such components are not eluted. In particular, the effect can be obtained when the substrate contains a metal capable of forming a complex ion with hydroxide ions, and more specifically, the substrate can be effectively applied to a substrate containing Al.

Specifically, the base substrate 11 is an anodized substrate in which an anodized film mainly composed of Al ₂ O ₃ is formed on at least one surface side of an Al base material mainly composed of Al. An anode in which an anodized film mainly composed of Al ₂ O ₃ is formed on at least one surface side of a composite base material in which an Al material mainly composed of Al is composited on at least one surface side of the Fe material Al ₂ O ₃ is a main component on at least one surface side of an oxide substrate and a base material on which an Al film having an Al main component is formed on at least one surface of an Fe material containing Fe as a main component. It is preferable that any one of the anodized substrates on which the anodized film to be formed is formed.

  Further, a soda lime glass (SLG) layer may be provided on the base substrate 11. By providing the soda lime glass layer, Na can be diffused into the photoelectric conversion semiconductor layer. When the photoelectric conversion semiconductor layer contains Na, the photoelectric conversion efficiency can be further improved.

  The lower electrode formed on the base substrate 11 is not particularly limited, and Mo, Cr, W, and combinations thereof are preferable, and Mo or the like is particularly preferable. The film thickness of the lower electrode is not limited and is preferably about 200 to 1000 nm. For example, a film can be formed on the substrate by a sputtering method.

  The main component of the photoelectric conversion semiconductor layer 13 provided on the lower electrode is not particularly limited, but is preferably a compound semiconductor having at least one chalcopyrite structure because high photoelectric conversion efficiency is obtained. More preferably, it is at least one compound semiconductor composed of an element, a group IIIb element, and a group VIb element.

As a main component of the photoelectric conversion semiconductor layer 13,
At least one group Ib element selected from the group consisting of Cu and Ag;
At least one group IIIb element selected from the group consisting of Al, Ga and In;
It is preferably at least one compound semiconductor comprising at least one VIb group element selected from the group consisting of S, Se, and Te.

As the compound semiconductor,
CuAlS ₂ , CuGaS ₂ , CuInS ₂ ,
CuAlSe ₂ , CuGaSe ₂ ,
AgAlS ₂ , AgGaS ₂ , AgInS ₂ ,
AgAlSe ₂ , AgGaSe ₂ , AgInSe ₂ ,
AgAlTe ₂ , AgGaTe ₂ , AgInTe ₂ ,
Cu (In, Al) Se ₂ , Cu (In, Ga) (S, Se) ₂ ,
Cu _1-z In _1-x Ga _x Se _2-y S _y (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 2, 0 ≦ z ≦ 1) (CI (G) S),
Examples include Ag (In, Ga) Se ₂ and Ag (In, Ga) (S, Se) ₂ .

Further, Cu ₂ ZnSnS ₄ , Cu ₂ ZnSnSe ₄ , Cu ₂ ZnSn (S, Se) ₄ , CdTe, (Cd, Zn) Te, or the like may be used.

  The film thickness of the photoelectric conversion semiconductor layer 13 is not particularly limited, and is preferably 1.0 to 4.0 μm, particularly preferably 1.5 to 3.5 μm.

  In addition, after forming the buffer layer in the CBD device of the present embodiment, the layer that functions as an electrode that captures light and is paired with the lower electrode and through which the current generated in the photoelectric conversion semiconductor layer flows. If a translucent conductive layer (for example, n-ZnO such as ZnO: Al) and an upper electrode (Al or the like) are formed, a photoelectric conversion element is completed. A photoelectric conversion element can be preferably used for a solar cell etc., A cover glass, a protective film, etc. can be attached to a photoelectric conversion element as needed, and it can be set as a solar cell.

  In addition, the photoelectric conversion element produced with the manufacturing method of this invention is applicable not only to a solar cell but other uses, such as CCD.

Examples of the present invention and comparative examples will be described.
As shown in FIG.

<Deposition substrate>
The film formation substrate is formed by laminating the lower electrode and the photoelectric conversion semiconductor layer 13 on the base substrate 11.
The substrate for film formation is an anodized substrate in which an aluminum anodic oxide film (AAO) is formed on an Al surface on a 100 μm thick stainless steel (SUS) -30 μm thick Al composite base material, and soda lime glass (SLG) on the AAO surface. The layer, the Mo electrode layer, and the photoelectric conversion semiconductor layer were sequentially formed. Specifically, an SLG layer and an Mo electrode layer were formed by sputtering, and a Cu (In _0.7 Ga _0.3 ) Se ₂ layer was formed as a photoelectric conversion semiconductor layer by a three-step method. The film thickness of each layer was SUS (100 μm), Al (30 μm), AAO (20 μm), SLG (0.2 μm), Mo (0.8 μm), CIGS (1.8 μm). The size of the substrate was 10 cm × 10 cm.

<Surface treatment>
A reaction vessel containing a 10% aqueous solution of KCN was prepared, and the surface of the CIGS layer, which is the surface of the film formation substrate, was immersed for 3 minutes at room temperature to remove impurities from the CIGS layer surface. After taking out, it fully washed with water.

<Preparation of reaction solution I>
Zinc sulfate aqueous solution (0.18 [M]) as aqueous solution (I) of component (Z), thiourea aqueous solution (thiourea 0.30 [M]) as aqueous solution (II) of component (S), component (C) Aqueous solution of trisodium citrate (0.18 [M]) was prepared as an aqueous solution (III), and aqueous ammonia (0.30 [M]) was prepared as an aqueous solution (IV) of component (N). Next, among these aqueous solutions, I, II, and III are mixed in the same volume, zinc sulfate 0.06 [M], thiourea 0.10 [M], trisodium citrate 0.06 [M]. A mixed solution was completed, and this mixed solution and 0.30 [M] aqueous ammonia were mixed in equal volumes to obtain a CBD solution (reaction solution). When mixing the aqueous solutions (I) to (IV), the aqueous solution (IV) was added last. In order to obtain a transparent reaction solution, it is important to add the aqueous solution (IV) last. The reaction solution obtained by mixing was filtered using a filtration filter having a pore size of 0.22 μm. The pH of the reaction solution finally obtained was 10.3.

<Preparation of reaction solution II>
CdSO ₄ aqueous solution, thiourea aqueous solution, and ammonia aqueous solution were mixed in predetermined amounts to prepare a CBD solution (reaction solution II) having CdSO ₄ : 0.0015M, thiourea: 0.05M, and ammonia: 1.5M. The pH of the reaction liquid II finally obtained was 12.0.

Example 1
The prepared film formation substrate was set on the substrate holding portion of the CBD apparatus shown in FIG.
Before bringing the surface of the substrate into contact with the reaction solution, the heater was turned on and the substrate was heated to 90 ° C.
Thereafter, as shown in FIG. 1, the substrate holding part was lowered and the substrate was immersed in the reaction solution I adjusted to 40 ° C., so that the buffer layer was deposited on the surface of the photoelectric conversion semiconductor layer. The deposition time was 30 minutes. During the deposition period, heating of the substrate with a heater (set temperature 90 ° C.) and temperature control of the reaction solution (set temperature 40 ° C.) were continued.

(Example 2)
In Example 2, the apparatus provided with the substrate holding portion 20 ′ shown in FIG. 3 having a flat substrate fixing surface in the CBD device shown in FIG. 1 was used. In Example 2, when the substrate was immersed in the reaction solution, the fixed surface was inserted so as to be inclined from the horizontal surface 2a as shown by a broken line in FIG. Except for this point, the buffer layer was deposited in the same manner as in Example 1.

(Example 3)
In Example 3, the same apparatus as in Example 2 was used. However, when the substrate was immersed in the reaction solution, the fixed surface was parallel to the horizontal surface 2a. Except for this point, the buffer layer was deposited in the same manner as in Examples 1 and 2.

Example 4
In Example 4, the CBD device 100 schematically shown in FIG. 4 was used. The CBD apparatus 100 corresponds to the reaction tank 103 capable of storing the reaction liquid 2, the opening 103a formed on the wall surface of the reaction tank 103, which is smaller than the size of the film formation substrate 10, and the opening 103a. And a substrate holding part (substrate holder) 104 for holding the film-forming substrate 10 so that the entire opening 103a is covered with the film-forming substrate 10 on the outer wall surface of the reaction vessel 103. A temperature control unit 110 and a substrate heating control unit 120 are provided.

  The substrate holder 104 pushes the back plate 106 (which also serves as a part of a constant-temperature water circulation path described later) capable of uniformly pressing the entire back surface of the substrate 10 toward the opening 103a. And a screw member 107 capable of pressing. The substrate holder 104 holds the substrate parallel to the side wall surface of the reaction vessel.

  The reaction liquid temperature control unit 110 includes a constant temperature water circulation path 112 for adjusting the temperature of the reaction liquid disposed outside the reaction tank 103 for circulating the constant temperature water 111 to heat or cool the reaction liquid 2 from the outside of the reaction tank 103, and a liquid A constant temperature bath 113 that maintains a constant temperature is provided.

  Further, the substrate heating control unit 120 includes a substrate heating constant temperature water circulation path 122 disposed on the substrate back surface for circulating the constant temperature water 121 for heating the substrate 10 from the substrate back surface, and a constant temperature bath for maintaining the liquid temperature constant. 123. In other words, the CBD device 100 has a mechanism (reaction solution temperature) that controls the reaction liquid introduced into the CBD device to a predetermined temperature separately from (independently from) the mechanism (substrate heating control unit 120) that heats the back surface of the substrate. The controller 110) is provided so that each temperature can be controlled independently.

  In Example 4, the film formation substrate was set on the substrate holder and heated to 90 ° C., and the reaction solution I adjusted to 40 ° C. was poured into the reaction vessel 15 minutes after the start of heating of the substrate. The buffer layer was deposited for a minute. During the deposition period of the buffer layer, the substrate heating control unit 120 and the reaction liquid temperature control unit 110 maintained the state where the 90 ° C. constant temperature water 121 and the 40 ° C. constant temperature water 122 were circulated, respectively.

(Example 5)
In Example 5, the same CBD apparatus as in Example 1 was used. The same procedure as in Example 1 was performed except that the reaction solution II was used, the substrate heating temperature was 80 ° C., and the film formation time was 4 minutes.

(Comparative Example 1)
In Comparative Example 1, the prepared reaction solution 2 is placed in a reaction vessel 150 made of a glass beaker schematically shown in FIG. 5, and the deposition substrate (substrate 10) is placed in the reaction vessel so that the deposition surface is on the bottom. In a standing state, the reaction vessel 150 was immersed in the constant temperature water 156 of the constant temperature bath 155 to heat the reaction solution to 90 ° C., and after heating to 90 ° C., the buffer layer was deposited for 60 minutes. In Comparative Example 1, the film formation substrate is heated via the reaction solution.

<Evaluation of film thickness>
In order to evaluate the thickness of the buffer layer coated with the CIGS layer, a protective film is formed on the surface of the buffer layer, and then a focused ion beam (FIB) process is performed to obtain a cross-section of the buffer layer. Carried out. The film thickness was measured for a total of 35 points from this cross-sectional SEM image, and the average value was calculated.
Specifically, 7 points were measured from the SEM image at each location for a total of 5 locations, a center point of a 10 cm square substrate and a location 3 cm above, below, left, and right from this center point. 35 points were measured, and the average film thickness and the standard deviation of the film thickness were calculated.

<Evaluation of the number of film surface particles>
In the field of view of 100 μm × 100 μm, the presence condition of the adhering material (aggregates discovered when the surface of the film is observed from directly above) in which the particles having the primary particle size of the order of several tens to several hundreds of nm are aggregated is evaluated according to the following criteria did.
Good when the equivalent circle diameter is 3 μm or more is 3 or less (◯), 4 or more when the equivalent circle diameter is 3 μm or more is acceptable (Δ), and the equivalent circle diameter is 3 μm or more The case where the number was 11 or more was regarded as defective (x).

<Evaluation of the degree of film loss due to bubble adhesion>
When film formation is performed on the CIGS layer by the CBD method, even if it is a very thin film of less than 100 nm, it is possible to visually confirm the presence of the film by its interference action. The part which could be determined not to have a film was confirmed. As a result of visual evaluation, when it corresponds to 5% or more of the substrate area, it is X when less than 5% but no film is attached, and ◯ when there is no film. did. Furthermore, about the sample which performed such evaluation, SEM observation was performed about the location visually recognized that the film | membrane is not attached, and the confirmation that the film | membrane was not attached was also performed.
In addition, when bubbles are present on the CIGS surface, the reaction liquid does not come into contact with the surface on which the reaction liquid is to be deposited.

<Evaluation of elution amount of substrate>
The amount of Al [ppm] eluted in the reaction solution after film formation was measured.
After depositing the buffer layers of the above Examples and Comparative Examples, 2.5 mL of CBD reaction solution was diluted with a 25 mL volumetric flask (10-fold dilution), and the Al concentration was measured using an SPS3000 ICP emission spectroscopic analyzer (lower limit of quantification). Value: Al (<1 ppm)). In addition, the measurement result was measured twice for each sample, and the average value of the obtained values was calculated.

  In each of Examples 1 to 5, since the substrate was immersed in the reaction solution in a state where the end face was protected, there was no elution of Al. Since the end surface of Comparative Example 1 was not protected, the Al amount of 31 ppm was eluted in the reaction solution after completion of the film formation.

As can be seen from Table 1, in the example using the production apparatus of the present invention, the adhesion of particles on the film formation surface could be satisfactorily suppressed.
In Examples 1 to 4, by setting the reaction solution temperature to be lower than the substrate temperature, the number of particles (colloid) attached was very small, and a good film was obtained. At this time, it is also clear that the reaction solution transmittance is 80% or more, and the generation of particles (colloid) is suppressed.

  Further, when the shape of the substrate holding part is a convex curve, it was possible to suppress film removal of the buffer layer. This is presumably because the bubbles rise along the curve and the bubble adhesion to the film formation surface is suppressed. In addition, even when the shape of the substrate holding portion is flat, the bubble adhesion to the film formation surface is suppressed as compared with the case where the substrate holding portion is tilted (Example 2) and the case where the substrate holding portion is not tilted (Example 3). It was possible to suppress film loss due to adhesion.

  In the examples, the standard deviation of the film thickness tended to be slightly smaller. The effect of the uniformity of film thickness in the present invention is expected to be manifested when the buffer layer is formed with a thicker film.

  In Examples 1 to 5, the inner wall of the reaction vessel was coated with Teflon (registered trademark), and the deposited film adhered to the inner wall was very little. On the other hand, in Comparative Example 1, the reaction vessel was a glass beaker, which was not coated with Teflon (registered trademark), and deposition of the deposited film on the inner wall was intense.

DESCRIPTION OF SYMBOLS 1 CBD apparatus 2 Reaction liquid 3 Reaction tank 10 Film-forming board | substrate 11 Base substrate 13 Photoelectric conversion semiconductor layer 20 Substrate holder (substrate holding part)
21 Stainless steel plate member 21a Fixed surface 22 Wall surface 23 Holder body 24 Liquid leakage prevention jig 25 Fixed frame 30 Heater 40 Reaction liquid temperature control unit 41 Temperature adjustment means 42 Temperature measurement unit

Claims (9)

A reaction vessel for storing a reaction liquid for depositing a film on the deposition surface of the deposition substrate;
A substrate holding unit for holding the film-forming substrate so that at least the film-forming surface is brought into contact with the reaction solution; and having a fixed surface made of stainless steel or titanium to which the back surface of the film-forming substrate is closely fixed.
A heater disposed on the back side of the fixed surface for heating the film-forming substrate from the back side of the film-forming substrate;
A chemical bath deposition apparatus comprising: a reaction liquid temperature control unit that controls the temperature of the reaction liquid in the reaction tank.   2. The chemical bath deposition apparatus according to claim 1, wherein the heater is a planar heater provided over an area larger than an area of the fixed surface on which the film-forming substrate is fixed.   The chemical bath deposition apparatus according to claim 2, wherein the heater is a rubber heater.   4. The chemical bath deposition apparatus according to claim 1, wherein the substrate holding unit holds the film formation substrate such that the film formation surface is vertically downward. 5.   The chemical bath deposition apparatus according to claim 4, wherein the fixed surface of the substrate holding portion is a convex curved surface.   The chemical bath deposition apparatus according to any one of claims 1 to 3, wherein the substrate holding unit is configured to hold the film-forming substrate so that the film-forming surface is inclined vertically downward.   The chemical bath deposition apparatus according to any one of claims 1 to 3, wherein the substrate holding unit holds the film-forming substrate in parallel with a side wall surface of the reaction vessel.   The said board | substrate holding part is equipped with the end surface protection member which prevents that the side end surface of the board | substrate fixed to the said fixing surface contacts the said reaction liquid. Chemical bath deposition equipment.   The chemical bath deposition apparatus according to any one of claims 1 to 8, wherein at least a portion of the inner wall of the reaction tank that is in contact with the reaction solution is coated with a hydrophobic material.