JP2013070032A - Manufacturing method of buffer layer and manufacturing method of photoelectric conversion element - Google Patents

Abstract

In a method for producing a buffer layer of a photoelectric conversion element by a CBD method, the generation of particles in a reaction solution is suppressed to reduce the cost, and the buffer layer film forming process can be shortened.
To A substrate holder 20, the deposition substrate 10 is mounted, by heating the substrate 10 so that the temperature T ₁ of _[° C.] by the heater 30, while keeping the heated state, from temperatures T ₁ At least the surface of the photoelectric conversion semiconductor layer 13 is brought into contact with the reaction liquid 2 whose temperature is controlled to a lower temperature T ₂ [° C.], and the formation of the buffer layer is started. The temperature T ₁ and the reaction liquid 2 are maintained at the temperature T ₂ .
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a buffer layer of a photoelectric conversion element using a chemical bath deposition method, and a method for manufacturing 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 solution 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 time can be provided. ing.

  Patent Document 3 proposes a method of heating the holding unit that holds the 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, since the generation of particles in the reaction solution can be suppressed, 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.

  On the other hand, in manufacturing a photoelectric conversion element, the buffer layer film formation process by the CBD method is a rate-determining factor for the manufacturing time of the photoelectric conversion element, and it is required to make the buffer layer film formation process in a shorter time. .

  The present invention has been made in view of the above circumstances, and in the method for producing a buffer layer by the CBD method, the generation of particles in the reaction solution is suppressed to reduce the cost, and the buffer layer forming step is shortened. It is an object of the present invention to provide a method for manufacturing a buffer layer that realizes time.

The method for producing a buffer layer of the present invention is a method for producing the buffer layer in a photoelectric conversion element having a laminated structure in which a lower electrode, a photoelectric conversion semiconductor layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate. Because
A reaction vessel for storing a reaction solution for depositing the buffer layer in a chemical bath, and a substrate holding unit for holding the substrate on which the photoelectric conversion semiconductor layer is laminated so that at least the surface of the photoelectric conversion semiconductor layer is in contact with the reaction solution. Using a device equipped with a heater for heating the substrate and a reaction liquid temperature control unit for controlling the temperature of the reaction liquid,
A substrate for film formation having a photoelectric conversion semiconductor layer on the outermost surface is attached to the substrate holding part,
The film-forming substrate is heated to the temperature T ₁ [° C.] by the heater,
The buffer layer is formed by bringing at least the surface of the photoelectric conversion semiconductor layer into contact with the reaction liquid adjusted to a temperature T ₂ [° C.] lower than the temperature T ₁ while maintaining the heating state of the film formation substrate. Start
During film formation of the buffer layer, the film formation substrate is maintained at a temperature T ₁ and the reaction liquid is maintained at a temperature T ₂ .

Here, it means that to maintain a temperature T _1, T ₂ is maintained a set temperature by a heater or the reaction liquid temperature control unit to T _1, T _2, respectively. For example, the actual temperatures of the film formation substrate and the reaction liquid may fluctuate immediately after the film formation substrate is brought into contact with the reaction liquid, but these temperatures are set to T ₁ and T ₂ , respectively ( The heater and the reaction liquid temperature controller function so as to approach T ₁ and T ₂ .

In particular, when forming a Zn-based compound layer as a buffer layer,
The relationship between the temperature T ₁ [° C.] and T ₂ [° C.]
T ₁ ≧ 70 ≧ T ₂ +30
It is preferable to satisfy.

  In the above, the Zn-based compound is any one of ZnS, Zn (S, O), and Zn (S, O, OH).

The method for producing a photoelectric conversion element of the present invention is a method for producing a photoelectric conversion element having a laminated structure in which a lower electrode, a photoelectric conversion semiconductor layer, a buffer layer, and a light-transmitting conductive layer are laminated on a substrate.
The buffer layer is manufactured by the method for manufacturing a buffer layer of the present invention.

According to the method for producing a buffer layer of the present invention, after the substrate is heated to a temperature T ₁ [° C.] with a heater, the reaction solution is adjusted to a temperature T ₂ [° C.] lower than the temperature T _1. Since at least the surface of the photoelectric conversion semiconductor layer is brought into contact, the precipitation starts at an early stage from the time when the substrate is immersed in the reaction solution, and the buffer is compared with the case where the temperature of the substrate is increased after the substrate is brought into contact with the reaction solution. The time required for forming the layer can be shortened.

  Further, by setting the substrate temperature at the time of film formation higher than that of the reaction solution, generation of particles (colloid) in the reaction solution can be suppressed, and film formation can be selectively performed on the substrate. Since the generation of particles (colloid) can be repeatedly used, the cost of the reaction liquid can be reduced.

Sectional drawing which shows schematic structure of an example of the manufacturing apparatus which enforces the manufacturing method of the buffer layer of this invention 1 is a perspective view of the manufacturing apparatus shown in FIG. Sectional schematic diagram which shows the photoelectric conversion element of one Embodiment manufactured by the manufacturing method of the photoelectric conversion element of this invention The schematic diagram which shows schematic structure of the CBD apparatus for enforcing the CBD method of Example 2. FIG. The schematic diagram which shows schematic structure of the CBD apparatus for enforcing the CBD method of the comparative example 2 The schematic diagram which shows schematic structure of the CBD apparatus for enforcing the CBD method of the comparative example 3

  Embodiments of the present invention will be described below.

First, a chemical bath deposition apparatus 1 (hereinafter referred to as a CBD apparatus 1) used in the manufacturing method of the embodiment will be described. FIG. 1 is a schematic cross-sectional view of the CBD device 1, and FIG. 2 is a perspective view showing a schematic configuration thereof.
As shown in FIG. 1, the CBD apparatus 1 includes a reaction tank 3 that stores a reaction solution 2, a substrate holder (substrate holder) 20 that holds a film formation substrate 10, and a film formation substrate 10 from the back side thereof. A heater 30 for heating and a reaction liquid temperature control unit 40 for controlling the temperature of the reaction liquid 2 in the reaction tank 3 are provided.

  The substrate holder 20 is a container having a plate-like member 21 provided with a fixed surface 21a to which the film-forming substrate 10 is closely fixed and having a bottom surface and a wall surface 22 continuously provided on the bottom surface made of the plate-like member 21. And a support portion 26 that is connected to the holder main body 23 and can be hooked on a part of the reaction vessel 3.

  Here, the fixed surface 21 a of the plate-like 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 formation substrate 10 is held so that the film formation surface faces vertically downward. 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 film formation, bubbles (gas) are generated in the reaction tank 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 shown in FIG. 1, it is possible to suppress the adhesion of bubbles and to realize better film formation. In this case, as the substrate 11 which is the base of the film formation substrate 10, a substrate having flexibility enough to bend along the curve of the fixed surface may be used.

  In addition, as a material of a plate-shaped member, stainless steel is preferable, and 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).

  Further, the substrate holder 20 faces the film-forming substrate 10 toward the substrate holder body 23 so that the film-forming substrate 10 can be brought into contact with the reaction liquid 2 only on the surface (film-forming surface) 10a. It is configured to be held by the liquid leakage prevention jig 24. 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.

  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 via the plate-like 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.

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.

  In the manufacturing method of the present embodiment, a photoelectric conversion element having a stacked structure in which a lower electrode, a photoelectric conversion semiconductor layer, a buffer layer, and a light-transmitting conductive layer are stacked on a substrate using the CBD device 1 described above. The buffer layer is manufactured.

A film formation substrate 10 for forming a buffer layer in which a lower electrode (not shown in FIGS. 1 and 2) and a photoelectric conversion semiconductor layer 13 are sequentially stacked is prepared on a substrate 11. Is mounted on the substrate holder 20. Then, heating the substrate 10 so that the temperature T _{1 [°} C.] by a heater.

After that, while maintaining the heating state of the film-forming substrate 10 (while heating the substrate 10 with a heater), at least the photoelectric conversion semiconductor is added to the reaction liquid adjusted to a temperature T ₂ [° C.] lower than the temperature T _1. The surface of the layer 13 is brought into contact. As shown in FIG. 1, the substrate 10 is immersed in the reaction solution together with the substrate holder 20, but the back surface of the substrate is in close contact with the fixing surface 15 of the holding unit 20 and fixed by the liquid leakage prevention jig 24 and the fixing frame 25. Therefore, the back surface and side end surfaces of the substrate do not come into contact with the reaction solution.

  Since the substrate 10 is heated before being immersed in the reaction solution, the buffer layer starts to be deposited early after the substrate 10 is immersed.

  Since the substrate 10 is sufficiently heated to the reaction temperature and then immersed in the reaction solution, the buffer layer starts to be deposited earlier than when the substrate is heated after the substrate is immersed. Therefore, the time required for film formation can be shortened. In particular, when a metal substrate is used as the substrate 10, it is possible to further promote the shortening of the film formation time because the heating rate of the substrate by heating is high.

During film formation, the substrate temperature is maintained at T ₁ by the heater 30, and the reaction liquid temperature is maintained at T ₂ by the reaction liquid temperature control unit 40. In addition, it is considered that the substrate temperature is temporarily lowered and the reaction solution temperature is temporarily increased by immersing the substrate in a reaction solution lower than T ₁ after heating the substrate to T _1. to T _1, it is assumed to maintain a controlled temperature by reaction temperature control unit 40 to T _2.

Here, the heating temperature T ₁ [° C.] of the substrate is set to a predetermined temperature (constant temperature) of 70 to 90 ° C., and the temperature adjustment temperature T ₂ [° C.] of the reaction solution is 60 ° C. or less, preferably 40 ° C. or less. The predetermined temperature (constant temperature) is preferable.
In particular, when a Zn-based compound layer is formed as the buffer layer, it is preferable that T ₁ ≧ 70 ≧ T ₂ +30. That is, T ₁ is preferably 70 ° C. or higher, and T ₁ and T ₂ are preferably set to have a temperature difference of 30 ° C. or higher.

  In addition, since the substrate heating temperature is set higher than the temperature control temperature of the reaction solution, a temperature distribution is generated in the reaction solution in the reaction tank 3 in the vicinity where the substrate is held and in a region away from the substrate. Here, the temperature of the reaction solution at a location sufficiently away from the substrate is measured as the reaction solution temperature. Specifically, as shown in the CBD device 1 of FIG. 1, the reaction liquid temperature adjustment means 41 is provided on the bottom surface side of the reaction tank 3 facing the vicinity of the water surface where the substrate is held, and the temperature measurement unit 42. Measures the temperature of the reaction solution near the bottom of the reaction vessel 3.

  If the substrate is 70 ° C. or higher, the temperature of the reaction solution in the vicinity where the substrate is immersed rises, and the buffer layer can be sufficiently deposited on the substrate. On the other hand, by lowering the set temperature of the reaction solution below the substrate temperature, the temperature of the reaction solution at a portion other than the vicinity of the substrate can be lowered to suppress generation of particles (colloid) in the reaction solution. it can. If the reaction solution is 60 ° C. or lower, the precipitation reaction can be greatly suppressed, and if it is 40 ° C. or lower, almost no particles (colloid) are generated.

The more particles (colloid) floating in the reaction liquid, the higher the possibility of particulate solids adhering to the surface of the deposited film. The particulate solid is a solid in which particles having a primary particle diameter of the order of several tens to several hundreds of nanometers are aggregated. If a photoelectric conversion element is produced with particulate solids (secondary aggregates) having an equivalent circle 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 is generated. 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.

  Since the temperature of the reaction solution is lower than the substrate temperature as in the production method of the present invention, the generation of particles (colloid) can be suppressed compared to the case where the entire reaction solution is set to the deposition temperature. Moreover, adhesion of particulate solids to the surface of the deposited film can also be suppressed. Further, since the substrate temperature is relatively high, selective film deposition on the substrate can be performed. If the inner wall of the reaction vessel is coated with Teflon (registered trademark), the effect of suppressing precipitation on the inner wall of the reaction vessel can be further enhanced. Further, by reducing the temperature of the reaction solution to 60 ° C. or lower, further 40 ° C. or lower, the generation of particles (colloid) can be more positively suppressed.

  The generation of particles (colloid) also promotes a decrease in the transmittance of the reaction solution (decrease in transparency), and the suppression of the particles (colloid) suppresses a decrease in the transmittance of the reaction solution (decrease in transparency). It is synonymous with that. As long as the transparency of the reaction solution is high, the reaction solution can be reused, so that the manufacturing cost of the buffer layer can be suppressed.

Further, from the viewpoint of suppressing generation of particles (colloid), it is preferable that the reaction solution is not stirred vigorously or not at all during film formation. 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.
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. And the temperature difference provided between the reaction liquid and the reaction liquid 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.

  After forming the buffer layer to a desired thickness, the substrate together with the substrate holder 20 is pulled up from the reaction solution, and the substrate on which the buffer layer is formed is removed from the substrate holder. Water is washed after the buffer layer is deposited, and water is removed by a water 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.

It should be noted that the formation of the buffer layer should be completed after the elapse of the film formation time at which a desired film thickness is obtained by checking the relationship between the film formation time and the film thickness under the preset conditions. do it.
Alternatively, the relationship between the change in the transmittance of the reaction solution and the film thickness is examined, the transmittance of the reaction solution is measured in-situ, and the film is formed based on the decrease in transmittance. You may make it complete | finish.

  Further, the relationship between the change in pH of the reaction solution and the film thickness of the reaction solution may be investigated, the pH of the reaction solution may be measured in situ, and the film formation may be terminated based on the amount of change in pH. Investigate the relationship between the change in the electric conductivity of the reaction solution and the film thickness, measure the electric conductivity of the reaction solution in situ, and finish the film formation based on the amount of change in the electric conductivity. It may be.

In the present invention, the buffer layer is formed by a chemical bath deposition (CBD) method.
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 in a supersaturated condition due to the equilibrium as a reaction solution (chemical bath deposition solution) and forming a complex of metal ion M, it can be formed at a moderate rate in a stable environment. In this method, a metal compound thin film is deposited on a substrate.

  Although it does not restrict | limit especially as a buffer layer, CdS, ZnS, Zn (S, O) and / or Zn (S, O, OH), InS, In (S, O), and / or In (S, O, OH) It is preferable that a metal sulfide containing Cd, Zn or In is used. The film thickness of the buffer layer is preferably 5 nm to 2 μm, more preferably 10 to 200 nm, and even more preferably 10 to 100 nm.

The chemical bath deposition solution (reaction solution) for depositing the buffer layer contains at least a metal (M) of Cd, Zn or In and a sulfur source. As a result, the buffer layer can be formed. As the sulfur source, compounds containing sulfur, for example, thiourea (CS (NH ₂ ) ₂ ), thioacetamide (C ₂ H ₅ NS), thiosemicarbazide, thiourethane, diethylamine, triethanolamine, etc. may be used. it can.

  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 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 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.

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 batch-type film formation, but the buffer layer according to the present invention is manufactured. The method is not limited to the one using the apparatus shown in FIG. 1, and can be applied to any CBD apparatus that can individually control the substrate temperature and the reaction liquid temperature.
Further, the production method of the present invention is not limited to the batch type, and can be applied to roll-to-roll type film formation.

Next, the manufacturing method of the photoelectric conversion element of this invention is demonstrated.
FIG. 3 shows a schematic cross-sectional view of a photoelectric conversion element of one embodiment manufactured by the method for manufacturing a photoelectric conversion element of the present invention. In order to facilitate visual recognition, the scale of each component in the figure is appropriately different from the actual one.

  3 includes a lower electrode (back electrode) 12, a photoelectric conversion semiconductor layer 13, a buffer layer 14, a window layer 15, a translucent conductive layer (transparent electrode) 16, and an upper electrode on a substrate 11. (Grid electrode) 17 is an element that is sequentially laminated.

  The method for producing a photoelectric conversion element of the present invention is a method for producing a photoelectric conversion element having a laminated structure of at least a lower electrode 12, a photoelectric conversion semiconductor layer 13, a buffer layer 14, and a light-transmitting conductive layer 16 on a substrate 11. The buffer layer is manufactured by the buffer layer manufacturing method of the present invention.

  There are no particular restrictions on the method of forming each layer other than the buffer layer. An example of the method for forming the substrate and each layer will be briefly described below.

(substrate)
Specifically, as the substrate 11,
Glass substrate,
A metal substrate such as stainless steel with an insulating film formed on the surface;
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 anodic oxide 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 combined on at least one surface side of the Fe material mainly composed of Fe. Formed anodized substrate,
An anodic oxide film mainly composed of Al ₂ O ₃ is formed on at least one surface side of a substrate on which an Al film composed mainly of Al is formed on at least one surface side of an Fe material mainly composed of Fe. Formed anodized substrate,
And a resin substrate such as polyimide.

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

As described above, the buffer layer manufacturing method of the present invention can be applied to a flexible substrate and a non-flexible substrate.
On the other hand, when the substrate fixing surface 21a of the substrate holder 20 is curved as shown in the CBD device 1 of FIG. 1, it is necessary to use a flexible substrate.
In addition, when using the apparatus which can protect the back surface and end surface of a board | substrate with a liquid leak prevention jig | tool and a fixed frame like the CBD apparatus 1 of FIG. 1, the board | substrate containing the component which melt | dissolves in a CBD reaction liquid Can be used. Specifically, the above-described anodized substrate containing Al that can form complex ions with hydroxide ions can be used.

(Lower electrode)
The main component of the lower electrode 12 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 12 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.

(Photoelectric conversion semiconductor layer)
The main component of the photoelectric conversion semiconductor layer 13 is not particularly limited and is preferably a compound semiconductor having at least one chalcopyrite structure because high photoelectric conversion efficiency can be obtained. The Ib group element, the IIIb group element, and the VIb More preferably, it is at least one compound semiconductor composed of a group 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.

  The method for forming the photoelectric conversion semiconductor layer 13 is not particularly limited, and can be formed by a vacuum deposition method, a sputtering method, an MOCVD method, or the like.

(Buffer layer)
The buffer layer 14 is manufactured by the above-described method for manufacturing a buffer layer of the present invention. The conductivity type of the buffer layer 14 is not particularly limited, and n-type or the like is preferable. The film thickness of the buffer layer 14 is not particularly limited, and is preferably 5 nm to 2 μm, more preferably 10 to 200 nm, and further preferably 10 to 100 nm. The details of the buffer layer are as described above.

(Window layer)
The window layer 15 is an intermediate layer that captures light. The composition of the window layer 15 is not particularly limited, and i-ZnO or the like is preferable. The film thickness of the window layer 15 is not particularly limited, preferably 10 nm to 2 μm, and more preferably 15 to 200 nm. The method for forming the window layer 15 is not particularly limited, but a sputtering method or an MOCVD method is suitable. On the other hand, since the buffer layer 14 is manufactured by the liquid phase method, it is also preferable to use the liquid phase method in order to simplify the manufacturing process. The window layer 15 is not essential and may be a photoelectric conversion element without the window layer 15.

(Translucent conductive layer)
The translucent conductive layer 16 is a layer that captures light and functions as an electrode that is paired with the lower electrode 12 and through which a current generated in the photoelectric conversion semiconductor layer 13 flows. The composition in particular of the translucent conductive layer 16 is not restrict | limited, n-ZnO, such as ZnO: Al, ZnO: Ga, ZnO: B, etc. are preferable. The film thickness of the translucent conductive layer 16 is not particularly limited, and is preferably 50 nm to 2 μm. The film forming method of the translucent conductive layer 16 is not particularly limited, but the sputtering method and the MOCVD method are suitable like the window layer. On the other hand, in order to simplify the manufacturing process, it is also preferable to use a liquid phase method.

(Upper electrode)
The main component of the upper electrode 17 is not particularly limited, and examples thereof include Al. The film thickness of the upper electrode 17 is not particularly limited and is preferably 0.1 to 3 μm.
In an integrated solar cell in which a large number of photoelectric conversion elements (cells) are integrated, the upper electrode is provided in a cell serving as a power extraction end among cells connected in series.

The photoelectric conversion element 5 manufactured by the manufacturing method of this embodiment is configured as described above.
The photoelectric conversion element 5 can be preferably used for a solar cell or the like. If necessary, a cover glass, a protective film, or the like can be attached to the photoelectric conversion element 5 to form 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 and comparative examples according to the present invention will be described.

<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 following two types of substrates for film formation were prepared.

(Deposition substrate I)
The film-forming substrate I 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. ) Layer, Mo electrode layer, and 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 I was 10 cm × 10 cm.

(Deposition substrate II)
The film formation substrate II was formed by forming a CIGS layer on a soda lime glass (SLG) substrate with an Mo electrode layer. Specifically, a Mo lower electrode is formed to a thickness of 0.8 μm on a soda lime glass (SLG) substrate by sputtering, and a Cu film having a thickness of 1.8 μm is formed on the Mo lower electrode by using a three-step method. A (In _0.7 Ga _0.3 ) Se ₂ layer was formed. The size of the substrate II was 3 cm × 3 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>
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]. The 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.

<CBD process>
Using the reaction solution prepared as described above, a Zn (S, O) film was formed as a buffer layer under the conditions of Examples and Comparative Examples.

For Examples 1 to 3, after satisfying the substrate heating temperature T ₁ > the temperature control temperature T ₂ of the reaction solution and heating the substrate to the temperature T ₁ in advance, the substrate was immersed in the reaction solution at the temperature T ₂ to form the buffer layer. Membrane was performed.
Each example and comparative example will be described. Each main condition is also listed in Table 1.

Example 1
In Example 1, the CBD device 1 shown in FIG. 1 was used.
The film-forming substrate I was set on a substrate holder, heated to 90 ° C., immersed in a reaction solution adjusted to 40 ° C. 15 minutes after the start of heating, and a buffer layer was deposited for 30 minutes.

(Example 2)
In Example 2, 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 presses the back plate 106 that can uniformly press the entire back surface of the substrate 10 (also serving as a part of a constant-temperature water circulation path described later) and the back plate 106 toward the opening 103a. And a screw member 107 that can be used.

  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. That is, the CBD device 100 is independent of the mechanism for heating the back surface of the substrate (substrate heating control unit 120) (independently), and the mechanism for controlling the reaction liquid introduced into the CBD apparatus to a predetermined temperature (reaction liquid temperature control). Part 110), and each temperature can be controlled independently.

  In Example 2, the film-forming substrate II was set on a substrate holder and heated to 90 ° C., and the reaction liquid adjusted to 40 ° C. was poured into the reaction vessel 15 minutes after the start of heating of the substrate II, The buffer layer was deposited for 30 minutes.

(Example 3)
The same CBD apparatus as in Example 2 was used.
The regulated temperature T ₂ of the reaction was brought 20 ° C., the deposition time except that a 120 min were the same as in Example 2.

(Comparative Example 1)
The same CBD apparatus as in Example 1 was used. However, a heater for heating the substrate is not used.
The film-forming substrate II was immersed in a reaction solution adjusted to 90 ° C. without heating, and then the buffer layer was deposited for 60 minutes.

(Comparative Example 2)
In the comparative example 2, as schematically shown in FIG. 5, a reaction tank 133 capable of storing the reaction liquid 2 and an opening formed on the wall surface of the reaction tank 133 that is smaller than the size of the film formation substrate. 133a and a substrate holder (substrate holder) that holds the film formation substrate 10 on the outer wall surface of the reaction tank 133 at a position corresponding to the opening 133a so that the entire opening is covered with the film formation substrate 10 A reaction pot 130 with 134 was used. The substrate holder 134 includes a back plate 136 capable of uniformly pressing the entire back surface of the substrate 10 and a screw member 137 capable of pressing the back plate 136 toward the opening 133a.
While holding the reaction liquid 2 in the reaction tank 133 and holding the film-forming substrate 10 by the substrate holder 134, the reaction pot 130 is immersed in the constant temperature water 141 of the constant temperature tank 140, thereby the entire reaction pot 130. Was heated to 90 ° C., and the buffer layer was deposited for 60 minutes. In this method, the reaction solution and the substrate are simultaneously heated to substantially the same temperature.

(Comparative Example 3)
In Comparative Example 3, the prepared reaction solution 2 is placed in a SUS reaction vessel 150 schematically shown in FIG. 6, and the film-forming substrate I (substrate 10) is stood in the reaction vessel so that the deposition surface faces downward. In this state, the reaction vessel 150 was immersed in the constant temperature water 156 of the constant temperature bath 155 to deposit the buffer layer for 60 minutes. In this method, the film-forming substrate I is heated via the reaction solution.

(Comparative Example 4)
The same CBD apparatus as in Example 1 was used.
The regulated temperature T ₂ of the reaction was brought 90 ° C., except that the same substrate heating temperature and the temperature control temperature was deposition of the buffer layer under the same conditions as in Example 1.

(Comparative Example 5)
The same CBD apparatus as in Example 1 was used.
The buffer layer was deposited under the same conditions as in Example 1 except that the substrate heating was started after the substrate was immersed in the reaction solution.

(Comparative Example 6)
A CBD device similar to that in Example 2 was used.
The film-forming substrate II was set on a substrate holder and heated to 40 ° C., and at the same time, the reaction solution adjusted to 40 ° C. was poured into the reaction vessel, and the buffer layer was deposited for 30 minutes. The heating start timing of the substrate holding part was simultaneous with the immersion in 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 is shown in Table 1.

<Membrane surface evaluation>
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 of 11 or more is shown in Table 1 as defective (x).

<Permeability of reaction solution>
The transmittance of the reaction solution after completion of the reaction was measured in the wavelength range of 200 nm to 800 nm, and the transmittance value at a wavelength of 550 nm is shown in Table 1.

  As shown in Table 1, by setting the reaction solution temperature lower than the substrate temperature as in Examples 1 to 3 and Comparative Example 5, the number of particles (colloids) attached is very small, and a good film can be obtained. It was. At this time, it is also clear that the reaction solution transmittance is 80% or more, and the generation of particles (colloid) is suppressed.

  In Example 3 where the temperature control temperature of the reaction solution was 20 ° C., the reaction solution permeability at the end of film formation was much higher than in Examples 1 and 2 where the temperature was 40 ° C. On the other hand, the deposition rate was slower than in Examples 1 and 2.

  On the other hand, Examples 1 and 2 and Comparative Example 5 have the same conditions for the substrate heating temperature and the reaction liquid temperature control temperature, but the deposition rates differ greatly between Examples and Comparative Examples. From this result, it is clear that the deposition rate is significantly increased by heating the substrate before the reaction solution is immersed. In Comparative Example 6 where the substrate temperature and the reaction temperature were both 40 ° C., no film was deposited.

DESCRIPTION OF SYMBOLS 1 CBD apparatus 2 Reaction liquid 3 Reaction tank 5 Photoelectric conversion element 10 Film-forming substrate 11 Substrate 12 Lower electrode 13 Photoelectric conversion semiconductor layer 14 Buffer layer 15 Window layer 16 Translucent conductive layer (transparent electrode)
17 Upper electrode (grid electrode)
20 Substrate holder (substrate holder)
21 Stainless steel plate member 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 (3)

A method for producing the buffer layer in a photoelectric conversion element having a stacked structure in which a lower electrode, a photoelectric conversion semiconductor layer, a buffer layer, and a light-transmitting conductive layer are stacked on a substrate,
A reaction tank for storing a reaction solution for depositing the buffer layer in a chemical bath and the substrate on which the photoelectric conversion semiconductor layer is laminated are held so that at least the surface of the photoelectric conversion semiconductor layer is in contact with the reaction solution. Using an apparatus comprising a substrate holding part, a heater for heating the substrate, and a reaction liquid temperature control part for controlling the temperature of the reaction liquid,
A substrate for film formation comprising a photoelectric conversion semiconductor layer on the outermost surface is attached to the substrate holding portion,
The film-forming substrate is heated by the heater so as to have a temperature T ₁ [° C.]
A buffer is prepared by bringing at least the surface of the photoelectric conversion semiconductor layer into contact with the reaction liquid adjusted to a temperature T ₂ [° C.] lower than the temperature T ₁ while maintaining the heating state of the film-forming substrate. Start depositing layers,
During the formation of the buffer layer, the buffer substrate manufacturing method is characterized by maintaining the film-forming substrate at the temperature T ₁ and the reaction liquid at the temperature T ₂ . When forming a Zn-based compound as the buffer layer,
The relationship between the temperature T ₁ [° C.] and T ₂ [° C.] is as follows:
T ₁ ≧ 70 ≧ T ₂ +30
The buffer layer manufacturing method according to claim 1, wherein: In the method of manufacturing a photoelectric conversion element having a stacked structure in which a lower electrode, a photoelectric conversion semiconductor layer, a buffer layer, and a light-transmitting conductive layer are stacked on a substrate,
The said buffer layer is manufactured with the manufacturing method of the buffer layer of Claim 1 or 2, The manufacturing method of the photoelectric conversion element characterized by the above-mentioned.