WO2013021564A1

WO2013021564A1 - Photoelectric conversion element manufacturing method

Info

Publication number: WO2013021564A1
Application number: PCT/JP2012/004739
Authority: WO
Inventors: 河野　哲夫; 真理子柿谷
Original assignee: 富士フイルム株式会社
Priority date: 2011-08-09
Filing date: 2012-07-25
Publication date: 2013-02-14
Also published as: JP2013038260A

Abstract

[Problem] To manufacture a photoelectric conversion element which is inexpensive and has good manufacturability, and wherein a good-quality stable pn junction is formed by a step of washing after pn junction formation. [Solution] A photoelectric conversion element manufacturing method comprises n passes of a washing step (where n > 1) of, after forming a pn junction by the wet method, washing at least an obverse face of a substrate on the side whereon the pn junction is formed. The washing step further comprises: a water wash step of washing the obverse face with water for a prescribed time; and an electrical conductivity measurement step of measuring electrical conductivity of the water after the water washing step. The washing step is carried out until the washing conditions of each pass of the n passes of the washing step are approximately identical, the electrical conductivity of the nth pass is lower than the electrical conductivity of the (n-1)th pass, and the electrical conductivity of the nth pass is 1.0mS/m or less.

Description

Method for manufacturing photoelectric conversion element

The present invention relates to a method for manufacturing a CI (G) S-based photoelectric conversion element.

A photoelectric conversion element provided with a photoelectric conversion semiconductor layer and an electrode connected to the photoelectric conversion semiconductor 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.

As compound semiconductor solar cells, there are known bulk systems such as GaAs systems and thin film systems such as CIS or CIGS systems composed of Ib group elements, IIIb group elements and VIb group elements. CI (G) S is a compound semiconductor represented by the general formula Cu1-zIn1-xGaxSe2-ySy (where 0≤x≤1, 0≤y≤2, 0≤z≤1), and x = 0 Is the CIS system, and when x> 0 is the CIGS system. Hereinafter, CIS and CIGS are collectively referred to as “CI (G) S”.

In a conventional thin film photoelectric conversion element such as a CI (G) S system, a CdS buffer layer or an environmental load is generally provided between a photoelectric conversion semiconductor layer and a translucent conductive layer (transparent electrode) formed thereon. In consideration of the above, a ZnS buffer layer not containing Cd is provided.

The buffer layer plays a role such as (1) prevention of recombination of photogenerated carriers, (2) band discontinuous matching, (3) lattice matching, and (4) coverage of surface irregularities of the photoelectric conversion semiconductor layer. In the CI (G) S system and the like, the surface unevenness of the photoelectric conversion semiconductor layer is relatively large, and it is preferable that the film is formed by a liquid phase method, particularly because it is necessary to satisfy the condition (4). The film is preferably formed by a CBD (ChemicalhemBath Deposition) method.

Furthermore, in order to satisfactorily satisfy the above conditions (1) to (3) in the buffer layer, formation of a stable pn junction with the photoelectric conversion semiconductor layer and a good interface with the translucent conductive layer Formation is necessary.

Impurities, for example, in the case of a CI (G) S-based photoelectric conversion semiconductor layer, impurities such as copper selenide and copper sulfide may remain on the surface of the photoelectric conversion semiconductor layer that forms the buffer layer. high. Such impurities inhibit stable pn junctions, and cause a deterioration in performance of CI (G) S thin film photoelectric conversion elements.

These impurities can be removed by surface treatment using a compound-containing aqueous solution having a cyano group or an amino group, such as an ammonia-containing aqueous solution or a potassium cyanide aqueous solution (KCN aqueous solution).

On the other hand, in film formation by the CBD method (wet method), precipitation of the target compound (buffer layer) on the photoelectric conversion semiconductor layer (reaction accompanied by heterogeneous nucleation) and precipitation of particles (colloid) in the reaction solution (Reaction accompanied by uniform nucleation) proceeds simultaneously, so that the particles generated in the solution are likely to adhere to the surface of the deposited film, and a buffer layer having particulate solid matter attached to the surface tends to be formed. Note that details of homogeneous nucleation and heterogeneous nucleation are described in Non-Patent Document 1, for example.

When a light-transmitting conductive layer is formed on the buffer layer in a state where particulate solids are attached, when a photoelectric conversion element is formed, only a region where the particulate solids are attached is particularly difficult to flow. The performance of the conversion element is degraded. In addition, the buffer layer in a state where the particulate solid is adhered may peel off when the light-transmitting conductive layer is formed, and at the same time, when a failure of the buffer layer occurs, the photoelectric conversion semiconductor In some cases, the layer is directly connected to the light-transmitting conductive layer, resulting in a leak path. Also in this case, the performance of the photoelectric conversion element is deteriorated.

In particular, particulate solids (also referred to as secondary aggregates or secondary particles) formed by agglomerating particles having a primary particle size on the order of several tens to several hundreds of nanometers are as large as a micron unit, and thus are described above. In addition, there is a high possibility that the performance of the photoelectric conversion element will deteriorate.

Moreover, it is preferable that no components of the reaction solution used in the CBD method remain on the buffer layer surface. The components of the reaction liquid remaining on the surface, in particular ammonia or ammonium compounds, are preferably removed in the same manner as the particulate solids because they can lower the bonding properties with the translucent conductive layer. The inventor has confirmed that such a decrease in bondability is significant when the light-transmitting conductive layer is formed by a vapor phase method such as sputtering. The decrease in bonding property due to the remaining components of the reaction solution is a problem that also exists when a pn homojunction formation by ion diffusion is performed by a liquid phase method without forming a buffer layer.

Therefore, it is preferable to remove particulate solids and remaining reaction liquid components on the surface of the buffer layer before forming the translucent conductive layer.

An attempt has been made to form a good quality buffer layer by removing a particulate solid on the surface of the buffer layer by providing a cleaning step on the surface of the buffer layer. In Patent Documents 1 to 3, pure water is used after the buffer layer is formed, and the cleaning process is performed by stirring cleaning (Patent Document 1), overflow cleaning (Patent Document 2), cleaning by bubbling (Patent Document 3), and the like. Moreover, in patent document 4, the washing | cleaning process using ammonia water is disclosed (Claim 5).

JP 2007-242646 A JP 2004-015039 A International Publication 2008/120306 Pamphlet Special table 2008-510310

However, in the above Patent Documents 1 to 4, although a device for improving the cleaning power has been devised, the process management in consideration of productivity and cost is not performed. It is preferable to clean the surface of the buffer layer sufficiently to keep the surface state as good as possible. However, in the cleaning process, the amount of cleaning liquid used and the process time should be as small as possible so that the cleaning effect can be sufficiently obtained. Is preferred.

The present invention has been made in view of the above circumstances, and includes a photoelectric conversion element having a high-quality and stable pn junction provided with a cleaning process after formation of a pn junction that is good in productivity and can be implemented at low cost. It aims at providing the manufacturing method of the photoelectric conversion element which can be manufactured.

The manufacturing method of the photoelectric conversion element of the present invention has a laminated structure of a lower electrode, a photoelectric conversion semiconductor layer, and a light-transmitting conductive layer on a substrate, and includes the photoelectric conversion semiconductor layer and the light-transmitting conductive layer. In a method for manufacturing a photoelectric conversion element having at least one pn junction in between,
A pn junction forming step of forming the pn junction by a wet method;
A cleaning step of cleaning at least the surface of the substrate on which the pn junction is formed, n times (n ≧ 2);
The washing step is a water washing step of washing the surface with water for a predetermined time;
An electrical conductivity measurement step for measuring the electrical conductivity of the water after the washing step,
The cleaning conditions for each of the n cleaning steps are substantially the same,
The cleaning step is performed until the n-th electrical conductivity is smaller than the (n-1) -th electrical conductivity and the n-th electrical conductivity is 1.0 mS / m or less. It is characterized by doing.

The method for producing a photoelectric conversion element of the present invention includes the following first to third preferred embodiments depending on the type of cleaning. That is, in the first to third preferred embodiments, the cleaning step after the pn junction forming step is different.

As a 1st suitable aspect of the manufacturing method of the photoelectric conversion element of this invention, the said water-washing process WHEREIN: In the said water of the capacity | capacitance of 2 ml or more per unit area of the said board | substrate stored in the washing tank of the said board | substrate The aspect which is a batch washing process of immersing and washing at least the surface for 5 seconds or more and 5 minutes or less is mentioned.

As a second preferred embodiment of the method for producing a photoelectric conversion element of the present invention, the water washing step is an overflow washing step in which at least the surface of the substrate is overflow washed using the water introduced into an overflow washing tank. The aspect which is is mentioned.

Moreover, as a 3rd suitable aspect of the manufacturing method of the photoelectric conversion element of this invention, the said water washing process supplies the said water at least to the said surface, and all the said water supplied from this shower member Is a shower cleaning process for cleaning the surface in a shower cleaning tank having a cleaning water storage tank for storing the electrical conductivity of the water stored in the cleaning water storage tank in the electrical conductivity measurement process. The mode which measures is mentioned.

In the method for producing a photoelectric conversion element of the present invention, pure water is preferable as the water before washing. Moreover, it is preferable to implement the said washing | cleaning process until the electrical conductivity of the said water after this washing | cleaning process is 1.0 mS / m or less and pH value becomes 7.0 or less.

The method for producing a photoelectric conversion element of the present invention can be preferably applied when the pn junction forming step is a buffer layer deposition step. Examples of the buffer layer deposition step include those carried out using a reaction solution containing ammonia or an ammonium compound.

The method for producing a photoelectric conversion element of the present invention can be preferably applied when the light-transmitting conductive layer is formed by a vapor phase method performed in a vacuum. Especially, it is suitable when forming a translucent conductive layer using a ZnO-based material by sputtering. The translucent conductive layer is preferably formed after an annealing step is performed after the buffer layer forming step.

The photoelectric conversion element manufacturing method of the present invention is a method for manufacturing a photoelectric conversion element in which a pn junction is formed by a wet method. As a guideline at the end of cleaning of a pn junction formation surface for obtaining a high-quality and stable pn junction, pn The present invention provides a new method using the electric conductivity of water used for cleaning the bonding surface. According to the present invention, it is possible to manufacture a photoelectric conversion element having a high-quality and stable pn junction provided with a cleaning step after forming a pn junction that is good in productivity and can be implemented at low cost.

It is a schematic sectional drawing which shows the layer structure of the photoelectric conversion element produced with the manufacturing method of this invention. It is the schematic which shows one Embodiment of the structure of the board | substrate used for a washing | cleaning process. It is the schematic which shows 1st Embodiment of the manufacturing method of the photoelectric conversion element of this invention (the 1). It is the schematic which shows 1st Embodiment of the manufacturing method of the photoelectric conversion element of this invention (the 2). It is the schematic which shows 2nd Embodiment of the manufacturing method of the photoelectric conversion element of this invention. It is the schematic which shows 3rd Embodiment of the manufacturing method of the photoelectric conversion element of this invention.

Hereinafter, the manufacturing method of the photoelectric conversion element of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing a layer structure of a photoelectric conversion element manufactured by the manufacturing method of the present invention. In the drawings of this specification, the scale of each part is appropriately changed and shown for easy visual recognition. In FIG. 1, only one photoelectric conversion element (cell) of an integrated solar cell is shown to show the layer structure of the photoelectric conversion element, but the manufacturing method of the present invention is an integration with a large number of photoelectric conversion elements. It is also suitable for the manufacture of a solar cell.

As shown in FIG. 1, the photoelectric conversion element 1 includes a substrate 10, a photoelectric conversion semiconductor layer 30 that generates hole / electron pairs by light absorption, a buffer layer 40, and a light-transmitting conductive material. This is an element in which a layer (transparent electrode) 50 and an upper electrode (grid electrode) 60 are sequentially laminated.

The photoelectric conversion element manufacturing method of the present invention is a method for manufacturing a photoelectric conversion element in which a pn junction is formed by a wet method. As a guideline at the end of cleaning of a pn junction formation surface for obtaining a high-quality and stable pn junction, pn The electrical conductivity of water used for cleaning the bonding surface is used.

Specifically, the substrate 10 has a stacked structure of the lower electrode 20, the photoelectric conversion semiconductor layer 30, and the light-transmitting conductive layer 50, and is interposed between the photoelectric conversion semiconductor layer 30 and the light-transmitting conductive layer 50. In the method for manufacturing a photoelectric conversion element having at least one pn junction,
a pn junction forming step of forming a pn junction by a wet method;
A cleaning step of cleaning at least the surface (pn junction forming surface) of the substrate 10 on which the pn junction is formed (n ≧ 2);
The washing step is a water washing step of washing the pn junction formation surface with water for a predetermined time;
An electrical conductivity measurement step for measuring the electrical conductivity of water after the water washing step,
The cleaning conditions for each of the n cleaning steps are substantially the same,
The cleaning process is performed until the n-th electrical conductivity is lower than the (n-1) -th electrical conductivity and the n-th electrical conductivity is 1.0 mS / m or less. Yes.

Here, the step of forming a pn junction by a wet method is specifically a step of forming the buffer layer 40 on the photoelectric conversion semiconductor layer 30 when the buffer layer 40 is provided as shown in FIG. When the buffer layer 40 is not formed, it is a step of forming a pn junction by doping a dopant having conductivity (p-type or n-type) different from that of the photoelectric conversion semiconductor layer 30.

Hereinafter, a method for producing a photoelectric conversion element of the present invention will be described by taking a photoelectric conversion element provided with a buffer layer 40 as shown in FIG. 1 as an example. In the method for manufacturing a photoelectric conversion element of the present invention, when the buffer layer 40 is formed by a wet process (pn junction formation), the cleaning after the formation of the buffer layer 40 necessary for obtaining a high-quality and stable pn junction is performed. The process has good productivity and can be carried out at low cost. Therefore, in the following description, first, a cleaning process will be described, and description of other layers will be described later.
"Washing process"

As described in the section “Background Art”, when the buffer layer 40 is formed by a wet method, the surface of the buffer layer 40 is formed with the components of the reaction solution used in the wet method and the particulates precipitated in the reaction solution. A solid material or the like is attached, and forming a light-transmitting conductive layer 50 or a window layer on the solid material with the attached substance causes a leak path and a decrease in bonding property, so that the quality is stable. A pn junction cannot be formed. In particular, when the buffer layer 40 is formed by the CBD method, a particulate solid tends to be easily formed.

The present inventor monitors the electric conductivity of the water after washing when washing the buffer layer surface 40s with water, and performs the washing until the electric conductivity becomes 1.0 mS / m or less. Thus, it has been found that a sufficient cleaning effect can be obtained to obtain a high-quality and stable pn junction with high productivity and low cost.

In the present invention, the cleaning of the surface 40s of the buffer layer 40 is performed using cleaning water (water). As the washing water L, pure water is preferable, but ion exchange water, industrial water, or a solution in which an additive having a colloid removing effect is added to water may be used. Although it is essential that the electrical conductivity of the cleaning water L used when judging the end of cleaning is 1.0 mS / m or less, for cleaning in a state where there are many deposits on the surface 40s, such as the first cleaning step. The cleaning water L supplied to the surface 40s is not necessarily fresh. The temperature of the washing water L is preferably 20 ° C. to 40 ° C.

In the cleaning process shown below, there is a possibility that the cleaning can be sufficiently performed by one cleaning process, but the cleaning is completed with the electrical conductivity being 1.0 mS / m or less because of insufficient cleaning. In order to prevent this from occurring, two or more n times (n ≧ 2) cleaning steps are performed, and n is determined from the electrical conductivity measurement value in the previous cleaning step (the (n-1) th cleaning step). By setting one of the determination items for the end of cleaning to be a low measured value of electrical conductivity at the second time, it is possible to perform cleaning with sufficient and good productivity.

If the cleaning of the surface 40s of the buffer layer 40 is performed until the electric conductivity of the cleaning water L after cleaning becomes 1.0 mS / m or less as described above, the productivity is low, the cost is high, and the quality is stable. A sufficient cleaning effect for obtaining a pn junction can be obtained, but it is more preferable that the cleaning is performed until the pH of the cleaning water L after cleaning becomes 7.0 or less.

After the cleaning with the cleaning water L, it is preferable to remove the cleaning water adhering to the cleaned substrate. The method for removing the washing water is not particularly limited, and examples thereof include a method of spraying dry air or nitrogen on the front and back surfaces of the substrate.

When the buffer layer is made of ZnS, Zn (S, O), Zn (S, O, OH), after the post CBD cleaning liquid removing step, the temperature is 150 ° C. to 250 ° C., preferably 170 ° C. It is preferable to provide a heat treatment process (annealing process) in which heating is performed at 210 ° C. for 5 minutes to 60 minutes. The heating atmosphere is not particularly limited in air or vacuum. The heating means is not particularly limited, but heating using a commercially available oven, electric furnace, vacuum oven or the like is preferable.

Hereinafter, a preferred aspect of the cleaning step in the method for producing a photoelectric conversion element of the present invention will be described. In the following description, the object to be cleaned is a laminated substrate B (hereinafter referred to as a substrate B) in which the lower electrode layer 20, the photoelectric conversion semiconductor layer 30, and the buffer layer 40 are formed on the substrate 10 (FIG. 2). The manufacturing method of the substrate B is not particularly limited except that the buffer layer 40 is manufactured by a wet method.

<First embodiment-Batch cleaning->
With reference to FIG. 3 (FIG. 3A, FIG. 3B), 1st Embodiment of the photoelectric conversion element of this invention is described. 3A and 3B are schematic views each showing an embodiment of the cleaning process of the first embodiment.

1st Embodiment is an aspect which implements a washing | cleaning process by a batch type, FIG. 3A is the aspect of the washing tank in the case of measuring electrical conductivity in the washing tank into which the board | substrate B which is a to-be-cleaned object is thrown in, FIG. 3B shows an aspect of the cleaning tank (cleaning apparatus) in the case where the cleaning water after cleaning is drained from the cleaning tank and the electrical conductivity is measured in another measuring tank. Although FIG. 3 shows the case where the number of substrates B to be loaded into the cleaning tank 100 is one, the number of substrates B to be loaded at a time may be plural.

In the first embodiment, as shown in FIG. 3A, the substrate B fixed to the substrate holding means 110 so that the surface 40 s of the buffer layer 40 is exposed is used as the cleaning water L stored in the cleaning tank 100. It is immersed and washed, and the electric conductivity of the washing water L after washing is measured by an electric conductivity meter 201. In the present embodiment, the cleaning tank 100 is provided with a cleaning water supply means 101 for supplying the cleaning water L and a draining means 102 for discharging the cleaning water after cleaning so that water can be poured and drained easily. However, the embodiment of the cleaning tank 100 is not limited to this.

In this embodiment, a pH meter 202 is also provided at the same time as the electrical conductivity meter 201. By setting it as this aspect, not only the electrical conductivity 201 of the washing water L after washing | cleaning but pH can be measured. As described above, the pH of the wash water L after washing is preferably 7.0 or less at the end of washing.

The first embodiment includes a washing step having a washing step of washing at least the surface 40s of the substrate B with the washing water L for a predetermined time and an electric conductivity measurement step of measuring the electric conductivity of the washing water L after the washing step. It has n times (n ≧ 2), the nth electric conductivity is lower than the (n−1) th electric conductivity, and the nth electric conductivity is 1.0 mS / m or less The cleaning process is carried out until The water washing process of the first embodiment is a batch washing process in which at least the surface 40 s is immersed in the washing water L having a capacity of 2 ml or more per unit area of the substrate B in the washing tank 100 and washed for 5 seconds or more and 5 minutes or less. is there. Here, the n-time cleaning process has substantially the same cleaning conditions. As in this embodiment, in the batch-type cleaning, the capacity and cleaning time of the cleaning water L stored in each cleaning tank 100 are substantially the same.

First, the substrate B held by the substrate holding means 110 is immersed in the cleaning water L for a predetermined time, and the surface 40s of the substrate B is cleaned with water for a predetermined time (water washing step). Cleaning can be carried out by simply immersing the substrate in the cleaning water L (still standing). However, by washing the substrate B, generating a water flow in the cleaning water L, generating ultrasonic waves, etc., per unit time The cleaning effect can be improved and the cleaning time can be shortened.

The immersion time (predetermined time) can be set according to the amount of the cleaning water L per unit area of the substrate B and the amount of deposits on the surface 40s of the buffer layer 40. Even if the time of one water washing is too long or too short, the productivity is lowered. In consideration of productivity, the time for one water washing is preferably 10 to 60 seconds.

The amount of the cleaning water L is not particularly limited as long as the volume is 2 ml or more per unit area of the surface area of the substrate B. If the amount is too small, the cleaning water L is contaminated in a short time, and it is necessary to provide a large number of cleaning steps in order to obtain a sufficient cleaning effect. When the surface 40s of the buffer layer 40 is about 3 cm square as the substrate B, it is preferable to use 50 to 150 ml of cleaning water L.

After the water washing step, after removing the substrate B, the electric conductivity of the washing water L in the washing tank 100 is measured by the electric conductivity meter 201 (electric conductivity measuring step). The electric conductivity meter 201 may be fixed to the cleaning tank 100 or may be a handy type that is not fixed.

In the mode of FIG. 3A, after one cleaning process is completed, the cleaning water L may be drained from the draining means 102 and then the cleaning water L may be supplied from the cleaning water supply means 101 to perform the next cleaning process. The cleaning tank 100 may be prepared, and after one cleaning step, the cleaning may be performed in another cleaning tank 100.

In the embodiment of the cleaning tank shown in FIG. 3B, the electrical conductivity measurement step can be performed in the measurement tank 200 different from the cleaning tank 100, and thus the substrate B is taken out from the cleaning water L when measuring the electrical conductivity. The electrical conductivity can be measured without any problems.

In the case of the cleaning tank shown in FIG. 3B, the draining means 102 after the water washing process is opened to inject the cleaning water after the cleaning into the measuring tank 200, and the cleaning water L after the cleaning is discharged from the cleaning tank 100. After completion, injection of fresh cleaning water L from the inlet 101 and measurement of electrical conductivity in the measuring tank 200 can be performed.

3B, the measuring tank 200 is provided with drain means 203 for draining the washing water L after the electrical conductivity measurement.

As will be described later in Examples, each of the photoelectric conversion elements 1 manufactured by cleaning the surface 40s of the buffer layer 40 by the above-described cleaning method has an energy conversion efficiency of 10% or more.

According to the cleaning method of the above embodiment, a photoelectric conversion element 1 having a high-quality and stable pn junction is provided, including a cleaning process after forming a pn junction that is good in productivity and can be performed at low cost. Can do.

<Second Embodiment-Overflow Cleaning->
A second embodiment of the photoelectric conversion element of the present invention will be described with reference to FIG. FIG. 4 is a schematic diagram illustrating a cleaning process according to the second embodiment.

In the second embodiment, the cleaning process is performed in an overflow manner. Although FIG. 4 shows the case where the number of substrates B to be introduced into the cleaning tank 100 is one, the number of substrates B to be introduced at a time may be plural.

In the second embodiment, as in the first embodiment, the substrate B fixed to the substrate holding unit 110 so that the surface 40 s of the buffer layer 40 is exposed is washed water L stored in the washing tank 100. The electrical conductivity of the cleaning water L after cleaning is measured with an electrical conductivity meter 201. In the second embodiment, cleaning water L is continuously supplied from the cleaning water supply means 101 to the cleaning tank 100 at least during the water washing process, and the cleaning water after washing overflowing from the drainage means (drainage channel) 102 is measured. It is an aspect that is injected into the tank 200. The measuring tank 200 is provided with a drain outlet and drains appropriately.

In this embodiment, the electrical conductivity measurement step is performed in the measurement tank 200. Similar to FIG. 3B, the measurement tank 200 is provided with an electric conductivity meter 201 and a pH meter 202.

In the second embodiment, the surface 40s of the substrate B is cleaned by overflow cleaning. Therefore, the cleaning time in the water washing process means the time from the start of cleaning (during the immersion of the substrate B) to the first electrical conductivity measurement, and the time of the electrical conductivity measurement interval.

Since the second embodiment is the same as the first embodiment except that an overflow washing tank is used, a washing process for washing at least the surface 40s of the substrate B with the washing water L for a predetermined time, and a washing water after the washing process. And n times (n ≧ 2) of cleaning steps including an electrical conductivity measurement step for measuring the electrical conductivity of L, and the nth electrical conductivity is smaller than the (n−1) th electrical conductivity. In addition, the cleaning process is performed until the n-th electrical conductivity is 1.0 mS / m or less.

Also in the second embodiment, the n-time cleaning process has substantially the same cleaning conditions. In the overflow type cleaning, the injection amount of the cleaning water L into the cleaning tank 100 per unit time and the electrical conductivity measurement interval (time) are substantially the same.

In the overflow cleaning, the larger the injection amount of the cleaning water L per unit time, the larger the amount of the cleaning water L that contacts the surface 40s of the substrate B per unit time. The injection amount of the cleaning water L per unit time can be appropriately designed according to the capacity of the cleaning tank 100, the number of substrates to be introduced, and the like.

Also in the overflow cleaning, the substrate B may be simply immersed in the cleaning water L (stationary) or may be vibrated.

The electrical conductivity measurement interval corresponds to the washing time in the first embodiment. Therefore, preferable conditions such as time are the same as the water washing time of the first embodiment.

FIG. 4 shows an aspect in which a measuring tank 200 is provided for collecting overflowing wash water and measuring electrical conductivity. The measurement of electrical conductivity may be carried out with respect to all the wash water overflowed at the time of the electrical conductivity measurement interval in the measurement tank 200, and may be carried out with respect to the wash water. When doing, it may implement with respect to the wash water stored in the measurement tank 200 within the storage time, limiting the storage time.

Further, the overflowed wash water may be measured by providing the conductivity meter 201 near the outlet of the drainage means without storing the overflow wash water in the measurement tank 200, for example.

Also in the cleaning method of the present embodiment, as in the first embodiment, a photoelectric conversion having a high-quality and stable pn junction provided with a cleaning process after forming a pn junction that is good in productivity and can be performed at low cost. Element 1 can be manufactured.

<Third embodiment-shower cleaning->
A third embodiment of the photoelectric conversion element of the present invention will be described with reference to FIG. FIG. 5 is a schematic view showing a cleaning process of the third embodiment.

In the third embodiment, the cleaning process is performed by shower cleaning. In the present embodiment, an example is shown in which a plurality (n (3)) of shower cleaning tanks (A1 to An (A3)) and a draining chamber B1 shown in FIG. 5 are provided in the substrate transport direction for cleaning. Although described, it is not limited to this mode.

The shower cleaning tank A (A1 to A3 (An)) includes a shower member (cleaning water supply means) 101 that supplies the cleaning water L to the surface 40s of the substrate B in a shower-like manner, and the cleaning water after cleaning. A cleaning water storage tank 103 that stores all the cleaning water L supplied from the member 101, and a drainage means 102 that drains the cleaning water L after cleaning stored in the storage tank 103 and pours it into the measurement tank 200. ing.

In the shower cleaning tank A, the distance between the shower member 101 and the substrate B is not particularly limited, but is preferably 10 cm to 30 cm.

In the third embodiment, unlike the first and second embodiments, the substrate holding unit 110 directs the substrate B, which is the object to be cleaned, with the surface 40s of the buffer layer 40, which is the cleaning surface, facing the cleaning water supply unit 101. It is the conveyance roller which conveys in a conveyance direction, hold | maintaining.

In the third embodiment, the water washing step is carried out in the shower washing tank A, and the electric conductivity measurement step is carried out by measuring the electric conductivity of the washing water stored in the washing water storage tank 103.

The cleaning water L is supplied from the shower member 101 to at least the surface 40s of the substrate B transferred to the shower cleaning tank A to clean the substances adhering to the surface 40s. While the cleaning water L is being supplied, the substrate B may be continuously transported in the transport direction, or may be transported after being stopped for a certain time for cleaning.

All the cleaning water L supplied from the shower member 101 including the cleaning water after cleaning is stored in a cleaning water storage tank 103 provided at the bottom of the shower cleaning tank A. In 3rd Embodiment, an electrical conductivity measurement process is implemented with respect to the wash water stored by this wash water storage tank 103. FIG.

FIG. 5 shows a mode in which the electrical conductivity measurement process is performed after the cleaning water stored in the cleaning water storage tank 103 is transferred to the measurement tank 200 by the drainage means 102. Such an aspect is preferable for the measurement of electrical conductivity and pH because it is easier to measure, but the electrical conductivity meter 201 and the pH meter 202 are directly installed in the washing water storage tank 103 without providing the measurement tank 200. You may implement an electrical conductivity measurement process and pH measurement.

In addition, the drainage means 102 connected to the washing water storage tank 103 is always opened and measures the electrical conductivity of the washing water stored in the measurement tank 200 at every electrical conductivity measurement interval. Alternatively, the drainage means 102 may be opened and drained at every electrical conductivity measurement interval, and the electrical conductivity may be measured for the wash water that has been drained and stored in the measurement tank 200. The measurement tank 200 is preferably provided with a drain outlet for draining the washed water after measurement.

Since this embodiment is the same as the first embodiment except that a shower washing tank is used, a washing process for washing at least the surface 40s of the substrate B with the washing water L for a predetermined time, and a washing water after the washing process. And n times (n ≧ 2) of cleaning steps including an electrical conductivity measurement step for measuring the electrical conductivity of L, and the nth electrical conductivity is smaller than the (n−1) th electrical conductivity. In addition, the cleaning process is performed until the n-th electrical conductivity is 1.0 mS / m or less.

Also in the third embodiment, the n-time cleaning process has substantially the same cleaning conditions. In the shower cleaning, the supply amount of cleaning water supplied from the cleaning water supply unit 101 per unit time and the electrical conductivity measurement interval (time) are substantially the same.

In shower cleaning, the larger the amount of cleaning water supplied from the cleaning water supply means 101 per unit time, the larger the amount of cleaning water L that contacts the surface 40s of the substrate B per unit time. Increases effectiveness. The supply amount of the cleaning water L per unit time can be appropriately designed according to the capacity of the cleaning water storage tank 103, the processing speed of the substrate to be transported, and the like.

FIG. 5 shows a mode in which the shower washing tank A is provided from A1 to A3. The number of shower cleaning tanks A is not particularly limited. For example, even when only one shower cleaning tank A is used, the drainage means 102 drains the cleaning water after cleaning from the cleaning water storage tank 103 at regular intervals so as not to overflow, and satisfies the above-described electrical conductivity conditions. If it is set as the aspect which stops conveyance of the board | substrate B until it does, the cleaning of this embodiment is possible.

In the case where a plurality of shower cleaning tanks A are provided, in order to eliminate useless cleaning, the cleaning water is not supplied from the cleaning water supply means 101 in the shower cleaning tank after the conditions for completion of the cleaning process are satisfied. It is preferable to make it.

When a plurality of shower cleaning tanks A are provided, the downstream shower cleaning tank (FIG. 5) is used as the cleaning water L in the upstream shower cleaning tank (A1 in FIG. 5) in order to suppress consumption of the cleaning water. 5 may use the waste water of A3).

In the embodiment shown in FIG. 5, it is preferable that a draining chamber B1 is provided. As the draining chamber B1, it is preferable that the cleaning water supplied by shower cleaning can be removed as much as possible, and it is preferable that the draining chamber B1 is constituted by an air knife or the like.

Also in this embodiment, as in the second embodiment, the electrical conductivity meter 201 is provided near the outlet of the drainage means 102 without storing the cleaning water drained from the cleaning water storage tank 103 in the measurement tank 200. May be measured.

"Other aspects of photoelectric conversion element"
In the method for manufacturing a photoelectric conversion element of the present invention excluding the washing step, there is no particular limitation except that the buffer layer 40 is formed by a wet method. The aspect of the photoelectric conversion element suitable for applying the manufacturing method of the photoelectric conversion element of this invention below is demonstrated. Since the manufacturing method is not limited except for the buffer layer 40, only the buffer layer 40 will be described.

The substrate 10 is not particularly limited, and a glass substrate, a metal substrate such as stainless steel having an insulating film formed on the surface, and Al ₂ O ₃ is mainly used on at least one surface side of an Al base material mainly composed of Al. An anodized substrate on which an anodized film as a component is formed,
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.

As a method for continuously forming a film, a so-called roll using a supply roll obtained by winding a long flexible substrate in a roll shape and a winding roll for winding a film-formed substrate in a roll shape Roll-to-Roll film formation process is known, but because it can be produced by this method, metal substrate with an insulating film formed on the surface, anodized substrate, resin substrate, etc. The flexible substrate is preferable.

In consideration of thermal expansion coefficient, heat resistance, substrate insulation, etc., an anodic oxide film mainly composed of Al ₂ O ₃ was formed on at least one surface side of an Al base composed mainly of Al. Anodized substrate, Al ₂ O ₃ as a main component on at least one surface side of a composite base material in which an Al material containing Al as a main component is combined on at least one surface side of an Fe material containing Fe as a main component An anodized substrate on which an anodized film is formed, and at least one surface side of a base material on which an Al film mainly composed of Al is formed on at least one surface side of an Fe material containing Fe as a main component It is preferable that any one of the anodized substrates on which an anodized film composed mainly of Al ₂ O ₃ is formed.

The lower electrode layer 20 is not particularly limited, and is preferably Mo, Cr, W, or a combination thereof, and Mo is particularly preferable. The thickness of the lower electrode layer 20 is not limited and is preferably about 200 to 1000 nm.

The main component of the photoelectric conversion semiconductor layer 30 is not particularly limited and is preferably a compound semiconductor having at least one chalcopyrite structure because high conversion efficiency is obtained. The Ib group element, the IIIb group element, and the VIb group More preferably, it is at least one compound semiconductor composed of an element.

As a main component of the photoelectric conversion semiconductor layer 30,
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) may be a _four.

The film thickness of the photoelectric conversion semiconductor layer 30 is not particularly limited, but is preferably 1.0 μm to 4.0 μm, and particularly preferably 1.5 μm to 3.5 μm.

There is a high possibility that impurities such as copper selenide and copper sulfide remain on the surface of the photoelectric conversion semiconductor layer 30 after film formation in the case of a CI (G) S-based photoelectric conversion semiconductor layer. Therefore, it is preferable to perform surface treatment for the purpose of removing impurities. As the surface treatment liquid used for such surface treatment, for example, an ammonia-containing aqueous solution, a compound-containing aqueous solution having a cyano group or an amino group can be used.

As the compound having a cyano group contained in the surface treatment liquid, potassium cyanide (KCN) is preferable. On the other hand, since KCN is a lethal compound and has a safety problem, it is more preferable to use a compound having an amino group.

The compound having an amino group contained in the surface treatment liquid is preferably a compound having at least two amino groups in one molecule (hereinafter also simply referred to as an amino group-containing compound). Specifically, ethylenediamine (EDA ), Diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), or pentaethylenehexamine (PEHA), and these are preferably used alone, Two or more types may be appropriately mixed and used.

These amino group-containing compounds are contained in the surface treatment solution in an amount of 1 to 30% by mass, preferably 5 to 25% by mass, and more preferably 10 to 20% by mass.

Hydrogen peroxide is contained in the surface treatment solution in an amount of 0.01 to 10% by mass, preferably 0.05 to 8% by mass, and more preferably 0.1 to 5% by mass.

The surface treatment solution can be prepared by dissolving the amino group-containing compound and hydrogen peroxide in water.

The time for bringing the photoelectric conversion semiconductor layer into contact with the surface treatment liquid depends on the concentration of the surface treatment liquid, but is preferably about several seconds to several tens of minutes.

By performing the surface treatment (impurity removal) as described above, the in-plane variation of the photoelectric conversion efficiency of the photoelectric conversion element can be reduced and the conversion efficiency can be increased.

When the surface treatment process is performed, it is preferable to wash the substrate with water. The temperature of water is preferably 20 ° C. or higher. Here, the water washing method may be a method of immersing in a water tank and washing with water or shower washing. As washing water, pure water, ion exchange water, industrial water, or the like can be used.

After rinsing with water, if the substrate is immersed in the reaction solution in the buffer layer 40 (pn junction) formation process by a wet method while water is attached to the substrate, the concentration of the reaction solution decreases. It is preferable to remove water to such an extent that the concentration is not diminished. Specifically, the water adhering to the substrate is removed by blowing dry air or nitrogen on the front and back surfaces of the substrate. At this time, warm air may be blown.

The inventor has found that it is preferable to form the buffer layer 40 (41, 42) within 60 minutes, preferably within 10 minutes after the surface treatment. Accordingly, the next buffer layer forming step is preferably performed within 60 minutes, preferably within 10 minutes after the surface treatment. Here, “within 60 minutes after the surface treatment” means a time from immediately after the completion of the surface treatment, and within 60 minutes including a water washing step and a drying step after the surface treatment.

The buffer layer 40 is not particularly limited as long as it has a function as a buffer layer of the photoelectric conversion semiconductor layer 30 and the translucent conductive layer 50. For the photoelectric conversion semiconductor layer 30, CdS, ZnS , Zn (S, O), Zn (S, O, OH) and the like are preferred.

As already described, in the method for manufacturing a photoelectric conversion element of the present invention, the buffer layer 40 is formed by a wet method. The method for forming the buffer layer 40 is not particularly limited as long as it is a wet method, but the CBD method is preferable.

The CBD method uses a general formula [M (L) _i ] ^{m +} ⇔M ^{n +} + iL (where M is a metal element such as Cd, Zn, In, Sn, L is a ligand, m, n, i: positive number) By using as a reaction solution a metal ion solution having a concentration and a pH that are in a supersaturated condition due to an equilibrium as represented by the following formula, a complex of metal ions M is formed at an appropriate rate in a stable environment. In this method, a metal compound thin film is deposited on a substrate.

Examples of the CBD reaction liquid include those containing a metal (M) source such as Cd or Zn and a sulfur source. Thereby, a buffer layer of CdS, ZnS, Zn (S, O), Zn (S, O, OH) can be formed. As the sulfur source, a compound 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.

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

In such a method, the reaction temperature is preferably 70 to 95 ° C. The reaction time may be about 5 to 60 minutes. CdS is a suitable material for the buffer layer, but Cd is highly toxic and is not preferable in terms of environmental load. Accordingly, the buffer layer 40 is more preferably a Cd-free metal compound, for example, a Zn compound layer mainly composed of Zn (S, O) and / or Zn (S, O, OH).

When the buffer layer 40 is a Zn compound layer mainly composed of Zn (S, O) and / or Zn (S, O, OH), at least one component (Z) as a zinc source, at least one A component (S) that is a sulfur source of the component, a component (C) that is at least one citric acid compound, a component (N) that is at least one selected from the group consisting of ammonia and an ammonium salt, and water. And the concentration of the component (C) is 0.001 to 0.25M, the concentration of the component (N) is 0.001 to 0.40M, and the pH before starting the reaction is 9.0 to 12.0M. It is preferable to use a reaction solution that is

Component (Z) is not particularly limited, and preferably includes at least one selected from the group consisting of zinc sulfate, zinc acetate, zinc nitrate, zinc chloride, zinc carbonate, and hydrates thereof. The concentration of component (Z) is not particularly limited and is preferably 0.001 to 0.5M.

Component (S) is not particularly limited and preferably contains thiourea. The concentration of component (S) is not particularly limited and is preferably 0.01 to 1.0M.

Component (C) is a component that functions as a complexing agent or the like, and a complex is easily formed by optimizing the type and concentration of component (C).

By using component (C), which is at least one kind of citric acid compound, a complex is more easily formed than in a reaction solution that does not use a citric acid compound, crystal growth by the CBD reaction is well controlled, and the base is covered well. Thus, a stable film can be formed.

Component (C) is not particularly limited, and preferably contains sodium citrate and / or a hydrate thereof. The concentration of component (C) is 0.001 to 0.25M. If the concentration of the component (C) is within this range, the complex is formed satisfactorily, and a film that satisfactorily covers the base can be stably formed. When the concentration of component (C) exceeds 0.25M, a stable aqueous solution in which the complex is well formed is obtained, but on the other hand, the progress of the precipitation reaction on the substrate is slow or the reaction does not proceed at all. There is. The concentration of component (C) is preferably 0.001 to 0.1M.

Component (N) is a component that functions as a pH adjuster or the like, but is also a component that functions as a complexing agent or the like. The ammonium salt suitable for use as the component (N) is not particularly limited, and examples thereof include NH ₄ OH.

The concentration of component (N) is 0.001 to 0.40M. The solubility and supersaturation degree of metal ions can be adjusted by adjusting the pH with the component (N). If the concentration of component (N) is within the range of 0.001 to 0.40M, the reaction rate is fast, and film formation is carried out at a practical production rate without providing a fine particle layer formation step before the film formation step. can do. When the concentration of the component (N) exceeds 0.40 M, the reaction rate becomes slow, and it is necessary to devise such as adding a fine particle layer before the film forming step. The concentration of component (N) is preferably 0.01 to 0.30M.

The pH of the reaction solution before starting the reaction is 9.0 to 12.0. When the pH of the reaction solution before the start of reaction is less than 9.0, the decomposition reaction of the component (S) such as thiourea does not proceed, or even if it proceeds, the precipitation reaction does not proceed. The decomposition reaction of thiourea is as follows. The decomposition reaction of thiourea is described in Journal of the Electrochemical Society, Vol. 141, pp. 205-210, 1994 and Journal of Crystal Growth, Vol. 299, pp. 136-141, 2007.
SC (NH ₂ ) ₂ + OH ^{− Ｓ} SH ⁻ + CH ₂ N ₂ + H ₂ O,
SH ⁻ + OH ⁻ ⇔S ² + H ₂ O.

When the pH of the reaction solution before the start of the reaction exceeds 12.0, the effect that the component (N) that also functions as a complexing agent or the like makes a stable solution increases, and the precipitation reaction does not proceed or proceeds. It will be very slow. The pH of the reaction solution before starting the reaction is preferably 9.5 to 11.5.

If the concentration of the component (N) is 0.001 to 0.40 M, the pH of the reaction solution before starting the reaction usually does not require special pH adjustment such as using a pH adjuster other than the component (N). Is in the range of 9.0 to 12.0.

The pH of the reaction solution after completion of the reaction is not particularly limited. The pH of the reaction solution after completion of the reaction is preferably 7.5 to 11.0. When the pH of the reaction solution after completion of the reaction is less than 7.5, it means that the reaction does not proceed, and it is meaningless when considering efficient production. In addition, if there is such a pH drop in a system containing ammonia that has a buffering effect, it is highly possible that ammonia has volatilized excessively in the heating process, and it is considered that manufacturing improvements are necessary. It is done. When the pH of the reaction solution after completion of the reaction is more than 11.0, the decomposition of thiourea is promoted, but since most of the zinc ions are stabilized as ammonium complexes, the progress of the precipitation reaction may be remarkably slowed. The pH of the reaction solution after completion of the reaction is more preferably 9.5 to 10.5.

In the above reaction solution, the pH of the reaction solution after the start of the reaction is usually in the range of 7.5 to 11.0 without special pH adjustment such as using a pH adjusting agent other than the component (N). .

The reaction temperature is 70 to 95 ° C. If the reaction temperature is less than 70 ° C., the reaction rate becomes slow, and the thin film does not grow, or even if the thin film is grown, it is difficult to obtain a desired thickness (for example, 50 nm or more) at a practical reaction rate. When the reaction temperature exceeds 95 ° C., generation of bubbles and the like increases in the reaction solution, which adheres to the film surface and makes it difficult to grow a flat and uniform film. Furthermore, when the reaction is carried out in an open system, a concentration change due to evaporation of the solvent or the like occurs, making it difficult to maintain stable thin film deposition conditions. The reaction temperature is preferably 80 to 90 ° C.

The reaction time is not particularly limited. Although the reaction time depends on the reaction 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.

Moreover, the reaction solution is aqueous. The pH of the reaction solution is not a strong acid condition. The pH of the reaction solution may be 11.0 to 12.0, but the reaction can be carried out under mild pH conditions of less than 11.0. The reaction temperature is not so high. Therefore, the environmental load is small and the damage to the substrate can be kept small.

The translucent conductive layer 50 is a layer that captures light and functions as an electrode that is paired with the lower electrode 20 and through which charges generated in the photoelectric conversion semiconductor layer 30 flow. The composition of the translucent conductive layer 50 is not particularly limited, and n-ZnO such as ZnO: Al, ZnO: Ga, and ZnO: B is preferable. The film thickness of the translucent conductive layer 50 is not particularly limited and is preferably 50 nm to 2 μm.

In the method for producing a photoelectric conversion element of the present invention, the deposit on the surface 40s of the buffer layer 40 is satisfactorily removed before the translucent conductive layer 50 is formed. As already described, in the case where deposits are present on the surface 40s of the buffer layer 40, adverse effects on the characteristics of the photoelectric conversion element are caused when a layer to be deposited thereon is deposited by vapor deposition such as sputtering. However, this adverse effect is suppressed in the present invention. Therefore, the film forming method of the translucent conductive layer 50 is not particularly limited, and a sputtering method or a MOCVD method, which are suitable film forming methods, can be applied. In addition, after forming the buffer layer 40, you may provide a window layer (protective layer) as needed. The window layer is an intermediate layer that captures light, and is provided in consideration of the band gap. In this case, the vapor phase method can also be applied to the film formation of the window layer.

The main component of the upper electrode 70 is not particularly limited, and examples thereof include Al. The thickness of the upper electrode 70 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.

Of course, the manufacturing process of the photoelectric conversion element described above may include other processes than the processes described above. For example, a patterning process for integration such as a scribing process of the lower electrode, a scribing process after forming the photoelectric conversion layer, a scribing process after forming the buffer layer and the transparent conductive layer, and one module when using a long substrate An integrated photoelectric conversion device (integrated solar cell) can be manufactured by adding a cutting process step or the like. Moreover, you may attach a cover glass, a protective film, etc. as needed.

"Design changes"
In the said embodiment, although the aspect provided with the buffer layer in the photoelectric conversion element was demonstrated, it can apply similarly also in the aspect which does not provide a buffer layer. In addition, before performing the cleaning step in the first to third embodiments, the surface of the substrate on the side where the pn junction is formed by a wet method may be cleaned by a simple cleaning method.

Examples and comparative examples according to the present invention will be described.

The photoelectric conversion element was produced as Examples 1-4 and Comparative Examples 1-3 by combining the board | substrate and each process which are shown below. Table 1 shows the presence / absence of each step that is not common in each example, combinations of conditions, and evaluation results.

(substrate)
A substrate having the following structure was used in common with all the examples and comparative examples.

On a 30 mm square soda-lime glass substrate (SLG substrate), a Mo lower electrode (0.8 μm thickness) and a Cu (In _0.7 Ga _0.3 ) Se ₂ layer (CIGS layer) (1.8 μm thickness) as a photoelectric conversion semiconductor layer Formed substrate. The Mo electrode layer was formed by sputtering, and the CIGS layer was formed by a three-stage method, which is a kind of multi-source deposition method.

(surface treatment)
For the surface treatment of the CIGS layer, a 10% aqueous solution of potassium cyanide (KCN) was used as the surface treatment solution. A reaction vessel containing a surface treatment solution was prepared, and the surface of the CIGS layer was immersed in a KCN aqueous solution at room temperature for 3 minutes to remove impurities from the CIGS layer surface.

(Water washing process after surface treatment)
After the surface treatment step, sufficient washing with pure water was performed. In the water washing, one substrate was first washed with 50 ml of pure water (primary cleaning). After removing the primary washing water, it was washed again with 100 ml of pure water (secondary washing), and after further removing the secondary washing water, it was similarly washed with 100 ml of pure water (tertiary washing). . The pH of the washing water after the third washing was 6.4. After washing with water, water was removed by blowing dry air.

(CBD process)
<Preparation of CBD reaction solution>
<< Reaction liquid 1 >>
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. Finally, this mixed solution was filtered using a filtration filter having a pore size of 0.22 μm to obtain CBD reaction solution 1. 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 pH of the obtained CBD reaction solution was 10.3.

<< Reaction liquid 2 >>
A predetermined amount of CdSO ₄ aqueous solution, thiourea aqueous solution, and aqueous ammonia solution were mixed to obtain CBD reaction solution 2 of CdSO ₄ 0.0015 M, thiourea 0.05 M, and ammonia 1.5 M. The pH of the obtained CBD reaction liquid was 12.0.

<CBD condition 1>
The substrate was immersed in the CBD reaction solution 1 adjusted to 90 ° C. and deposited for 60 minutes.

<CBD condition 2>
The substrate was immersed in a CBD reaction solution 2 adjusted to 80 ° C., and deposition was performed for 6 minutes.

(Cleaning process after buffer layer deposition)
After the buffer layer was deposited by the CBD process, pure water was used as a cleaning solution, and sufficient cleaning was performed under the conditions shown in Table 1. The electrical conductivity during washing was measured using a conductivity meter CM-31P manufactured by Toa DKK, and the pH was measured using a pH meter HM-31P manufactured by Toa DKK. After cleaning, the cleaning liquid was removed by blowing dry air.

(Annealing treatment)
Annealing treatment was performed in air at 200 ° C. for 60 minutes.

(Element formation of examples and comparative examples)
After forming an Al-doped conductive zinc oxide thin film on the buffer layer by a sputtering method, an Al electrode is formed as an upper electrode by a vapor deposition method, and then a scribe process is performed on a 30 mm × 30 mm substrate cut out. Eight converter elements (single cell solar cell, light receiving area 0.516 cm ² ) were produced. Eight cells were produced for each example and comparative example shown in Table 1.

(Evaluation methods)
About each Example and the comparative example, the buffer layer film thickness, the presence or absence of peeling generation | occurrence | production, the grade of peeling generation | occurrence | production, and the photoelectric conversion efficiency were measured and evaluated. The evaluation for peeling was performed both when the translucent conductive layer was formed on the day after the formation of the buffer layer and when it was carried out two weeks after the formation of the buffer layer.

<Measurement of buffer layer thickness>
For the samples prepared by the methods of Examples 1 to 4 and Comparative Examples 1 to 3, the thickness of the buffer layer is evaluated at the stage where the buffer layer is formed on the CIGS layer or at the stage where the photoelectric conversion element is manufactured. For this purpose, after forming a protective film on the sample surface, focused ion beam (FIB) processing was performed to extract the cross section of the buffer layer, and SEM observation was performed on the cross section. The film thickness was measured at a total of 35 locations from this cross-sectional SEM image. Table 1 shows the average value of the film thickness measurement values.

<Measurement of photoelectric conversion efficiency>
The photoelectric conversion efficiency was measured for each of eight cells for each example and comparative example. Table 1 shows average values of photoelectric conversion efficiencies for eight cells obtained for each of the examples and comparative examples.

About each produced cell, the energy conversion efficiency was measured on the conditions of the artificial sunlight of Air Mass (AM) = 1.5 and 100 mW / cm < ² > using the solar simulator. In addition, this measurement was implemented after performing light irradiation for 30 minutes. In Table 1, those having an energy conversion efficiency of 10% or more are shown as “◯” and those having less than 10% as “X”. As shown in Table 1, the effectiveness of the present invention was confirmed.

The manufacturing method of the photoelectric conversion element of this invention is applicable to the photoelectric conversion element used for a solar cell, an infrared sensor, etc.

Claims

A photoelectric conversion having a laminated structure of a lower electrode, a photoelectric conversion semiconductor layer, and a light-transmitting conductive layer on a substrate, and having at least one pn junction between the photoelectric conversion semiconductor layer and the light-transmitting conductive layer. In the manufacturing method of the element,
A pn junction forming step of forming the pn junction by a wet method;
A cleaning step of cleaning at least the surface of the substrate on which the pn junction is formed, n times (n ≧ 2);
The washing step is a water washing step of washing the surface with water for a predetermined time;
An electrical conductivity measurement step for measuring the electrical conductivity of the water after the washing step,
The cleaning conditions for each of the n cleaning steps are substantially the same,
The cleaning step is performed until the n-th electrical conductivity is smaller than the (n-1) -th electrical conductivity and the n-th electrical conductivity is 1.0 mS / m or less. A method for producing a photoelectric conversion element, comprising:
The water washing step is a batch washing step in which at least the surface of the substrate is immersed in the water having a capacity of 2 ml or more per unit area of the substrate stored in a washing tank and washed for 5 seconds to 5 minutes. It exists, The manufacturing method of the photoelectric conversion element of Claim 1 characterized by the above-mentioned.
2. The method for manufacturing a photoelectric conversion element according to claim 1, wherein the water washing step is an overflow washing step in which at least the surface of the substrate is overflow washed using the water introduced into an overflow washing tank. .
The said water washing process wash | cleans the said surface in the shower washing tank provided with the shower member which supplies the said water at least to the said surface, and the washing water storage tank which stores all the said water supplied from this shower member Shower cleaning process,
2. The method for manufacturing a photoelectric conversion element according to claim 1, wherein in the electrical conductivity measurement step, electrical conductivity of the water stored in the washing water storage tank is measured.
The method for producing a photoelectric conversion element according to any one of claims 1 to 4, wherein pure water is used as the water before washing.
The washing step is carried out until the electric conductivity of the water after the washing step is 1.0 mS / m or less and the pH value is 7.0 or less. The manufacturing method of the photoelectric conversion element in any one of.
The method for manufacturing a photoelectric conversion element according to any one of claims 1 to 6, wherein the pn junction forming step is a buffer layer deposition step.
The method for producing a photoelectric conversion element according to claim 7, wherein the buffer layer deposition step is performed using a reaction solution containing ammonia or an ammonium compound.
The method for manufacturing a photoelectric conversion element according to any one of claims 1 to 8, wherein the light-transmitting conductive layer is formed by a vapor phase method performed in a vacuum.
The method for manufacturing a photoelectric conversion element according to claim 9, wherein the translucent conductive layer is formed by a sputtering method.
The method for producing a photoelectric conversion element according to any one of claims 1 to 10, wherein the translucent conductive layer is a ZnO-based translucent conductive layer.
The method for manufacturing a photoelectric conversion element according to any one of claims 1 to 11, wherein the light-transmitting conductive layer is formed after an annealing step is performed after the buffer layer forming step.