JP2002116160A - Method of measuring impurity concentration of cadmium telluride powder and method of making film of cadmium telluride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method of measuring the concentrations of trace quantities of impurities in CdTe powder and to provide a CdTe film of good quality and a solar battery of excellent output characteristics at a low cost by enabling the CdTe powder for formation of the CdTe film to be quickly and appropriately evaluated prior to its use. SOLUTION: The ratio of the atomic concentrations of Cd, Te and a third element, which is calculated from multi-point measurements with an X-ray microanalyzer, is plotted onto a triangle chart whose apexes represent the three elements; the ratio of the number of atoms in each impurity (metal Cd, metal Te and oxygen compound or the like) to the total number of atoms in a sample is calculated from the ratio, to the total number of measuring points, of the number of measuring points where the atomic concentration ratio is plotted in a predetermined area on the triangle chart, which area is characteristic of each impurity. This measuring method is used for calculating the atomic number ratio of the impurities and a CdTe film is manufactured by proximate sublimation method using the evaluated raw CdTe powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the impurity concentration in cadmium telluride (CdTe) powder and a method for producing a CdTe film using CdTe powder as a raw material.

[0002]

2. Description of the Related Art CdTe powder is produced by proximity sublimation (CSS).
As a raw material in the production of a CdTe film. In many cases, the CdTe film is used as a p-type semiconductor layer of a CdTe-based solar cell. In a method of forming a CdTe film by the CSS method, a source holder provided with a raw material layer containing CdTe as a main component and a thin film forming substrate are provided with a small gap therebetween, and generally, an inert gas is used. In this method, the raw material is heated to a higher temperature than the substrate for forming a thin film and sublimated in an atmosphere to deposit CdTe on the substrate for forming a thin film.

The CSS method has been disclosed by TL Chu et al. (The Conference Record of the 22nd IEEE).
Photovoltaic Specialists Conference (1991) Vol. 2,
p952-956), for example, as a raw material 5N
Using high-purity polycrystalline CdTe or polycrystalline CdTe obtained by directly synthesizing constituent elements and dopants. In this film forming method, Cd having good crystallinity is used.
Although a Te film can be obtained, it is a disadvantage that the raw material is extremely expensive.

For this reason, general industrial raw materials include C
d powder and Te powder are mixed, and heated to 700 ° C. or more in an inert gas, and the produced CdTe is pulverized into commercially available Cd.
Te powder is used. However, this commercial CdTe
In the case of using powder, Cd from which impurities in the raw material were obtained
It deteriorates the crystalline state of the Te film. Therefore, these impurities have a significant adverse effect on the characteristics of a solar cell using a CdTe film.

[0005] The above-mentioned commercially available CdTe powder often contains metallic Te as an impurity. When Te powder, which is a starting material for producing CdTe powder, is blended in an excess molar ratio with respect to Cd powder, the resulting CdTe
Unreacted Te remains in the powder and is contained as an impurity. Conversely, when the molar ratio of Cd is excessive, unreacted Cd
In addition, a small amount (about several hundred ppm) of unreacted Te often remains. This is presumably because Cd has a lower vaporization temperature than Te, so that Cd is likely to be preferentially vaporized and scattered below the CdTe generation temperature, and the amount of Cd that should react with Te decreases. Therefore, commercially available CdTe powder, which is a general raw material, contains metal Te and metal CdTe.
Is an unavoidable problem that exists as an impurity.

For example, in the manufacturing process of a CdS / CdTe solar cell, Cd is deposited on a thin film forming substrate on which a transparent conductive film and a cadmium sulfide (CdS) film are sequentially formed by a CSS method.
A Te film is formed. If metal Te is present in the raw material in this case, it vaporizes at a low temperature in preference to CdTe. Therefore, before the formation of the CdTe film, the vapor of Te
Reacts with and erodes the dS film. As a result, significant irregularities occur on the surface of the CdS film, and the bonding with the CdTe film is hindered. When erosion is significant, pinholes are generated on the surface of the CdS film, and a CdTe film is partially formed on the exposed underlying transparent conductive film. When such a CdTe film is used, the photoelectric characteristics of the solar cell are significantly deteriorated. Therefore, in order to form a good CdTe film or to manufacture a solar cell having excellent photoelectric characteristics, it is necessary to use a CdTe powder whose impurity content is reduced to a level at which there is substantially no adverse effect as a raw material.

Tens of thousands to thousands of ppm in the above CdTe powder
A large amount of impurities can be quantified by, for example, X-ray diffraction, chemical analysis, or the like. However, there is no method for quantitatively and easily measuring a trace amount of impurities of several tens to several thousand ppm. Therefore, it was very difficult to analyze and evaluate the raw materials for each lot before use. as a result,
The characteristics of the obtained CdTe film or a solar cell manufactured using the same were not stable, and the yield was extremely poor.

Conventionally, prior to the production of a CdTe film, a CdTe film or a solar cell is prototyped in advance using a sample of a raw material collected for each lot, and the characteristics of the prototype are evaluated. It was necessary to judge the quality of the raw material lot. However, this method requires a lot of man-hours and a long time until the evaluation result of the raw material lot is found out, thus preventing mass production.

[0009]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a method for simply and accurately quantifying trace impurities such as Te and Cd in CdTe powder. Further, by applying this method, a raw material for forming a CdTe film is quickly and appropriately evaluated to form a high-quality and inexpensive CdTe film, and CdS / Cd having excellent photoelectric characteristics.
An object is to provide a Te solar cell.

[0010]

The method for measuring the impurity concentration of a CdTe powder according to the present invention comprises the steps of:
d, metal Te, and a method for measuring the concentration of an impurity composed of a compound containing a third element, wherein a multi-point measurement of the sample is performed by an X-ray microanalyzer, and Cd, Te, and the atomic concentration ratio of the three elements consisting of the third element are plotted on a triangular diagram having the three elements as vertices, and the atomic concentration ratio in a predetermined region specific to each of the impurities on the triangular diagram is plotted. The number of measurement points on which the ratio is plotted is determined, and the ratio of the number of atoms in each impurity to the total number of atoms in the sample is determined from the ratio of the number of measurement points to the total number of measurement points. According to the method for measuring the impurity concentration of the present invention, metal Te, metal Cd, and the third element, which are impurities in the CdTe powder, can be accurately quantified by a simple method.

In the method for measuring the impurity concentration of CdTe powder according to the present invention, when the third element is oxygen, CdT
The predetermined region unique to e and each impurity is defined as follows. 1) The atomic concentration ratio of Cd and Te (Cd atomic concentration / Te atomic concentration) on the triangular diagram is 3/2 or more, and the atomic concentration ratio of Cd and oxygen (Cd atomic concentration / oxygen atomic concentration) is 3/2. The above-mentioned region is defined as the predetermined region unique to the metal Cd, and the ratio of the number of atoms of the metal Cd to the total number of atoms in the sample can be obtained. 2) A region where the atomic concentration ratio of Cd and Te on the triangular diagram is 2/3 or less and the atomic concentration ratio of Te and oxygen (Te atomic concentration / oxygen atomic concentration) is 3/2 or more is defined as metal Te. By defining the specific predetermined region, a ratio of the number of atoms of the metal Te to the total number of atoms in the sample can be obtained. 3) A region where the atomic concentration ratio of Cd and Te on a straight line connecting each vertex of Cd and Te on the triangular diagram exceeds 2/3 and is less than 3/2, and the atoms of Cd and Te on the triangular diagram Concentration ratio is 3
/ 2 or more and the atomic concentration ratio of Cd and oxygen is 3/2 or more, and the atomic concentration ratio of Cd and Te on the triangular diagram is 2/3 or less and the atomic concentration ratio of tellurium and oxygen is 3 A region excluding three regions of / 2 or more is defined as the predetermined region unique to the oxygen compound, and the ratio of the number of oxygen atoms in the oxygen compound to the total number of atoms in the sample can be determined. .

In the method for producing a CdTe film of the present invention, each of the elements (Cd, Te, and Cd) in each of the impurities is determined based on the total number of atoms in a sample previously collected from a lot of the raw CdTe powder by the measurement method according to the present invention. A ratio of the number of atoms of (oxygen) is determined, and a CdTe powder lot whose ratio satisfies a predetermined condition is used as a raw material, and CdTe is obtained by proximity sublimation.
It forms a film. According to the present invention, CdTe powder used as a raw material can be quickly and appropriately evaluated before use, and as a result, a high quality CdTe powder which does not erode the underlying film such as a CdS film and has good bonding properties with the underlying material. The film can be efficiently manufactured with high yield.

CdT formed by the manufacturing method of the present invention
By using the e film as a p-type semiconductor, a solar cell with high conversion efficiency can be provided at low cost.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When CdTe powder is left in the air, unreacted Te and Cd in the CdTe powder are easily oxidized to tellurium oxide and cadmium oxide. Oxygen in these oxygen compounds hinders the formation of a high-quality CdTe film, as in the case of the aforementioned metal Te and metal Cd. Therefore, in the measurement of impurities in the CdTe powder, the third element other than Te and Cd (particularly, T
It is important to determine the amount of oxygen atoms contained in oxygen compounds of e and Cd. As the compound containing the third element,
In addition to the above oxygen compounds, there are iron, copper, oxides thereof, and the like which are mixed in the step of preparing the CdTe powder or are originally contained in the Cd powder or Te powder as a raw material. According to the present invention, the ratio of the number of atoms to the total number of atoms in the sample can be obtained for the metal Te, metal Cd, and the third element such as oxygen, iron, or copper contained in the CdTe powder as impurities. .

In the method for measuring the impurity concentration of CdTe powder according to the present invention, first, multi-point measurement of the CdTe powder is performed by an X-ray microanalyzer, and the C at each measurement point is measured.
The atomic concentration ratio of three elements consisting of d, Te, and the third element is plotted on a triangular diagram having the three elements as vertices. Atomic concentration of each element at each of the above measurement points, the peak intensity of the X-ray microanalyzer measured at each measurement point, the relationship between the previously measured peak intensity and the atomic concentration of the element in the standard sample, Required from. As a standard sample, it is necessary to select a compound in which the ratio of the bonded atoms is accurately grasped.

For example, in order to determine the relationship between the peak intensity of Cd or Te and the atomic concentration, it is convenient to select a CdTe single crystal in which Cd atoms and Te atoms are bonded 1: 1 as a standard sample. is there. The peak intensity of Cd by X-ray microanalyzer of CdTe single crystal is x, Te
Is the peak intensity of y, x is 50% of Cd atoms, and y is y.
Indicates the peak intensity when Te atoms are present at a concentration of 50%. Assuming that the peak intensity of Cd measured at each measurement point of the CdTe powder sample is x ₁ and the peak intensity of Te is y ₁ , the atomic concentration of Cd is (x ₁ / x) ×
The atomic concentration of Te is obtained as (y ₁ / y) × 50%.

As a standard sample for determining the atomic concentration of oxygen or iron as the third element, for example, F
It is sufficient to select a powder of FeO that is guaranteed that e is bonded exactly to oxygen with 1: 1. In this case, Fe
When the peak intensity of oxygen of the O standard sample is a, the peak intensity of iron is b, the peak intensity of oxygen at each measurement point is a ₁ , and the peak intensity of iron is b ₁ , the atomic concentration of oxygen at each measurement point is (A ₁ / a) × 50%, the atomic concentration of iron is (b ₁ / b) × 5
0%. In order to determine the atomic concentration of oxygen or copper, a powder of CuO may be used as a standard sample.

In the measuring method according to the present invention, the measuring accuracy can be improved as the number of measuring points by the X-ray microanalyzer is increased. For example, by setting the total number of measuring points to 100,000 or more, the number contained in the CdTe powder can be improved. Tens to thousands
It is possible to quantify even a very small amount of impurities having an atomic ratio of about pm.

When the component at the measurement point is only metal Cd, the atomic concentration ratio (Cd: Te: O) at that point is 1: 0:
Since it is 0, it should be plotted on the vertex of Cd on the triangular diagram. However, since the beam diameter of the X-ray for measurement applied to the sample by the X-ray microanalyzer is actually larger than the atomic level, when an attempt is made to measure a portion where metal Cd as an impurity exists, the surrounding area is not measured. Cd
Under the influence of Te or the like, a slight Te peak other than Cd may be detected. Therefore, the atomic concentration ratio obtained from these peak intensities is Te from the top of Cd.
It is often plotted at a position shifted to the side. For the same reason, when the component at the measurement point is only metal Te, the atomic concentration ratio is often plotted at a position shifted from the top of Te to the Cd side.

The atomic concentration ratio of CdTe is theoretically the point where Cd: Te: oxygen is 1/2: 1/2: 0, that is, pure C
dTe should be plotted only at the center point on the line connecting the vertices of Cd and Te. However, in practice, when measuring a powdery pure CdTe sample, in addition to the CdTe particles at the location to be measured, the influence of Te atoms and Cd atoms in adjacent particles having different crystal orientations is obtained. The atomic concentration ratio is often plotted at a position shifted from the center point to the Te or Cd side.

Therefore, the present inventors considered that pure CdTe and impurities accurately weighed thereto (Cd powder, Te powder,
And CdTeO ₃ powder) were added to prepare samples with various known impurity concentrations, and these samples with known concentrations were subjected to multipoint measurement using the X-ray microanalyzer described above.
The degree of the shift was examined experimentally. Then, the present inventors collated the state where the atomic concentration ratio obtained at each measurement point was plotted on a triangular diagram with the known atomic number ratio of each element in the sample with a known concentration, thereby obtaining the CdTe powder. A method for finding the ratio of the number of atoms of each element in each impurity (Cd atom in metal Cd, Te atom in metal Te, and oxygen atom in oxygen compound) to the total number of atoms was found.

That is, in the triangular diagram of FIG. 1, when the atomic concentration ratio (Cd / Te) of Cd and Te is 3/2 or more, Cd
The ratio of the number of measurement points plotted in an equilateral triangular region 1 (hereinafter referred to as a Cd region) having an atomic concentration ratio (Cd / oxygen) of 3/2 or more to the total number of measurement points is represented by the total number of atoms in the sample. Considering the ratio of the number of atoms of metal Cd to the number of atoms, Cd
/ Te is 2/3 or less, and the atomic concentration ratio of Te and oxygen (Te
/ Oxygen) is an equilateral triangular region 2 (hereinafter Te)
Is regarded as the ratio of the number of atoms of metal Te to the total number of atoms in the sample, whereby the ratio that most closely matches the known atomic number ratio is considered. Was found to be required.

Further, a straight line portion 3 where Cd / Te on the line connecting the vertices of Cd and Te is more than 2/3 and less than 3/2.
The ratio of the number of measurement points plotted in the area (hereinafter referred to as CdTe area) to the total number of measurement points is represented by Cd
It was found that by considering the molar ratio of Te, the molar concentration of CdTe most consistent with the purity of the sample of known concentration was determined. Further, the Cd region 1, T in the triangular diagram of FIG.
The ratio of the number of measurement points plotted in the remaining region 4 (hereinafter, oxygen compound region) excluding the region 2 of e and the region 3 of CdTe to the total number of measurement points is represented by the ratio of oxygen atoms to the total number of atoms in the sample. It was found that by considering the ratio of the number of atoms, a ratio most consistent with the known ratio of the number of atoms was obtained.

In the method for producing a CdTe film of the present invention, an impurity concentration of a sample collected from a raw material cadmium telluride powder is measured by the method for measuring an impurity concentration of a CdTe powder according to the present invention, and the metal concentration relative to the total number of atoms in the sample is measured. T
A raw material cadmium telluride powder in which the ratio of the number of atoms of e is 1000 ppm or less, the ratio of the number of oxygen atoms is 5000 ppm or less, or the number of atoms of metal Cd is not less than the number of atoms of metal Te is disposed on the source holder. The cadmium telluride powder is heated and vaporized to form a cadmium telluride film on a thin film forming substrate disposed close to and opposed to the source holder.

CdTe powder contains metal Te as an impurity.
Is ideally not contained at all,
Even if a trace amount of 000 ppm or less is contained, substantially no erosion of the underlying CdS is observed, and a good CdS / CdTe interface and a CdTe film having good crystallinity can be obtained. However, when a CdTe powder containing metal Te in an atomic ratio greater than 1000 ppm is used,
It is unavoidable that the underlying CdS film is eroded and a part where CdS is partially removed and irregularities occur.

When a large amount of oxygen compounds of Cd and Te are present in the CdTe powder, the amount of Cd and Te used for forming a thin film is reduced, so that a high-density CdTe film is not formed and the quality of the CdTe film is deteriorated. I do. When the temperature of the substrate for forming a thin film is as high as 500 ° C. or higher, oxygen in the oxygen compound oxidizes the underlying CdS to cause a defect on the CdS surface, failing to obtain a good CdS / CdTe interface. . The ratio of the number of oxygen atoms in the CdTe powder is 5000
At a low rate of less than ppm, the above problem hardly occurs.

Since Cd vaporizes at a lower temperature than Te, the CdT in which the metal Cd remains more than the metal Te
By using e powder as a raw material, erosion of the underlying CdS by Te is prevented. Thereby, good CdS
/ CdTe interface is obtained, and a CdTe film having good crystallinity is obtained.

In the solar cell according to the present invention, a transparent conductive film and a CdS film as an n-type semiconductor are sequentially formed on a translucent insulating substrate, and CdTe as a p-type semiconductor is formed on the CdS film by the manufacturing method of the present invention. It is a film formed. ADVANTAGE OF THE INVENTION By this invention, the crystallinity of the CdTe film | membrane of CdS / CdTe interface improves, In particular, the spectral sensitivity characteristic in the wavelength of 500-650 nanometer is excellent, a short circuit current is large, and the solar cell of high conversion efficiency can be provided. .

[0029]

Next, the present invention will be described in more detail with reference to examples.

Example 1 First, with respect to a standard sample (CdTe single crystal and FeO having an atomic ratio of exactly 1: 1), the peak intensities of Cd, Te, and oxygen by an X-ray microanalyzer, The relationship with the atomic concentration was determined. As a result, the peak intensity of Cd corresponding to the atomic concentration of Cd of 50% was 3,862 counts, the peak intensity of Te corresponding to the atomic concentration of Te of 1987 was 1987, and the peak intensity of oxygen corresponding to the atomic concentration of oxygen of 50%. Was 3708 counts.

Next, various CdTe powder samples were spread on a 2 mm square sample table, respectively, and the peak intensities of one million Cd, Te and oxygen were measured by an X-ray microanalyzer. With each of these measured peak intensities,
Atomic concentration of each element 50% previously determined from the standard sample
From the relationship with each peak intensity at the time of Cd, Td at each measurement point
The atomic concentrations of the three elements e and oxygen and their ratios were calculated by a computer in an X-ray microanalyzer, and the calculated atomic concentration ratios were plotted on a triangular diagram by a plotter in the device.

First, a powder obtained by pulverizing a CdTe single crystal was selected as a measurement sample, and the atomic concentration ratio of each measurement point obtained by the above method was plotted on a triangular diagram. In this case, the atomic concentration ratios of many measurement points are plotted at the midpoint between the vertices of Cd and Te in FIG. 1 as in the case of the CdTe single crystal, and within the region 3 of CdTe shown in FIG. The atomic concentration ratio of all measurement points was plotted. Next, various samples of known amounts of metal Cd were prepared by changing the amount of Cd powder added to the powder obtained by pulverizing the CdTe single crystal, and the atomic concentration ratio of each measurement point was determined for each of the samples by the method described above. And plotted on a triangular diagram. In this case, the atomic concentration ratio of each measurement point was plotted in the equilateral triangle of the Cd region 1 in addition to the CdTe region 3. Table 1 shows the metal C in each sample.
The relation between the known atomic number ratio of d and the atomic number ratio obtained by the present invention is shown.

[0033]

[Table 1]

As shown in Table 1, the known atomic number ratio of metal Cd and the atomic number ratio of Cd obtained from the ratio of the number of measurement points where the atomic concentration ratio is plotted in region 1 of Cd to the total number of measurement points are as follows. , Cd in an atomic ratio of 10 to 10
Quantitatively good agreement was obtained in all samples changed in the range of 000 ppm. From this, by regarding the ratio of the number of measurement points plotted within the range of the region 1 of the metal Cd to the total number of measurement points as the atomic ratio of the metal Cd in the CdTe powder, the concentration of the metal Cd in each sample was substantially reduced. It was confirmed that the measurement could be performed quantitatively. Incidentally, as a result of measuring the X-ray diffraction pattern of each CdTe powder, it was found that metal Cd was 1000
A slight Cd peak was observed in the sample added at the atomic ratio of 0 ppm, but in all other samples, the Cd peak was observed.
No peak other than Te was observed.

Next, various samples with known amounts of metal Te were prepared by changing the amount of Te powder added to the powder obtained by pulverizing the CdTe single crystal, and the samples at the respective measurement points were determined by the method described above. The concentration ratio was determined and plotted on a triangular diagram. In this case, the atomic concentration ratio of each measurement point is determined by the CdTe.
In addition to the area 3 of, the plot was also made in the equilateral triangle of the area 2 of Te. Table 2 shows the relationship between the known atomic ratio of metal Te in each sample and the atomic ratio determined according to the present invention.

[0036]

[Table 2]

As shown in Table 2, the known atomic number ratio of metal Te and the atomic number of metal Te obtained from the ratio of the number of measurement points where the atomic concentration ratio is plotted in region 2 of metal Te to the total number of measurement points The ratio refers to a ratio of the number of atoms of metal Te of 10
Quantitative agreement was good in all samples changed in the range of 10000 ppm to 10000 ppm. From this, the ratio of the number of measurement points plotted in the region 2 of metal Te to the total number of measurement points is regarded as the ratio of the number of atoms of metal Te in the CdTe powder, whereby the concentration of metal Te in each sample is almost quantitatively determined. It was confirmed that measurement was possible. In addition, as a result of measuring the X-ray diffraction pattern of each CdTe powder, Te
No Te peak was observed in any samples other than the sample added at the atomic ratio of pm.

Further, by changing the amount of CdTeO ₃ powder added to the powder obtained by pulverizing the CdTe single crystal, various samples having a known oxygen atom ratio were prepared.
The atomic concentration ratio at each measurement point was determined by the method described above, and plotted on a triangular diagram. In this case, the atomic concentration ratio at each measurement point was plotted in the oxygen compound region 4 in addition to the CdTe region 3. Table 3 shows the relationship between the known oxygen atom number ratios of various CdTeO ₃ added samples and the oxygen atom number ratios measured according to the present invention.

[0039]

[Table 3]

As shown in Table 3, the known oxygen atom number ratio of each sample and the oxygen atom number ratio obtained from the ratio of the number of measurement points at which the atomic concentration ratio was plotted in the oxygen compound region 4 to the total number of measurement points were obtained. Has an oxygen atom ratio of 7.5 to 750.
Quantitative agreement was good in all samples changed in the range of 0 ppm. From this, the ratio of the number of measurement points plotted in the oxygen compound region 4 to the total number of measurement points is expressed as C
It was confirmed that the concentration of the oxygen compound in each sample can be measured almost quantitatively by considering the ratio of the number of oxygen atoms in the dTe powder. As a result of measuring the X-ray diffraction pattern of each CdTe powder, the measured value of the oxygen atom number ratio was 1000.
No CdTeO ₃ peak was observed in any samples other than the 0 ppm sample.

In this embodiment, oxygen is taken as an example of the third element other than Cd and Te. However, when measuring impurities such as copper or iron other than oxygen as the third element, oxygen is used as the third element. By plotting the atomic concentration ratio obtained by replacing the element with the third element on a triangular diagram, the atomic number ratio of the third element other than oxygen can be obtained by the same method.

Example 2 Various CdTe films were formed using, as raw materials, CdTe powders having the same composition as the samples shown in Table 2 in which the atomic ratio of metal Te was determined in Example 1. FIG. 2 shows the arrangement of the main members at the time of film formation. The raw material layer 7 and the thin film forming substrate 9 are 3 m apart from each other via a spacer 8.
The temperature of the substrate 9 for thin film formation is set to 550 ° C., the temperature of the source holder 6 is set to 150 ° C. higher than the temperature of the substrate 9 for thin film formation, and the thin film is formed in a nitrogen atmosphere. CdTe film 1 having a thickness of about 5 μm on the surface of
3 was formed.

The thin film forming substrate 9 is formed by forming a 5000-Å-thick transparent conductive film 11 of tin oxide on a glass substrate 10 of 3 mm and 10 mm square made of borosilicate glass by a chemical vapor deposition method. Then, cadmium diethyldithiocarbamate is thermally decomposed to a thickness of 800
An Angstrom CdS film 12 was formed.
A carbon plate having a thickness of 3 mm and 10 mm square was used for the source holder 6, and the raw material layer 7 was formed by spreading a powdery raw material on the source holder 6 to a substantially uniform thickness.

For each CdTe film produced using each raw material, an X-ray diffraction pattern was measured and a chemical analysis was performed. As a result, all the films were oriented in the (111) plane, and the atomic ratio of Cd and Te in the films was almost 1: 1.
As a result of observing a cross section near the interface between the CdS film and the CdTe film by SEM, the measured atomic ratio of metal Te in Table 2 was 1000.
When CdTe powder exceeding ppm is used, CdS
A part where the membrane was eroded and missing was partially observed. This is because Te sublimated prior to CdTe film formation is CdS
This may be the result of erosion of the membrane. In particular, when a CdTe powder in which the atomic ratio of metal Te exceeds 5000 ppm is used, a large pinhole in the CdS film and the C
Pinholes were also observed in the dTe film. On the other hand, metal Te
When CdTe powder having an atomic ratio of 1000 ppm or less was used, it was confirmed that the CdS film was not eroded in any case.

SnO ₂ / CdT where CdS is missing
e CdS / CdTe at the interface and where there is no CdS erosion
TEM observation of the interface was performed. As a result, SnO ₂ / Cd
There were many places where the CdTe atomic arrangement was irregular near the Te interface, and a regular atomic arrangement could be confirmed near the CdS / CdTe interface. From the above, the atomic ratio of metal Te measured by the measurement method shown in Example 1 was 1000 p.
It has been clarified that the use of a CdTe powder of pm or less as a raw material improves the interface state between the CdS film and the CdTe film, and further improves the crystallinity of the CdTe film formed thereon.

Example 3 A method similar to that of Example 2 was used except that each CdTe powder having the same composition as the sample shown in Table 3 in which the atomic ratio of oxygen was measured in Example 1 was used as a raw material. A CdTe film was produced.

Each Cd of Example 3 produced using each raw material
The X-ray diffraction pattern of the Te film was measured. As a result, it was confirmed that all the films were oriented in the (111) plane.
Further, as a result of chemical analysis of each CdTe film, the ratio of the number of atoms of Cd to Te in each film was almost 1: 1. Also,
As a result of observing the cross section near the interface between the CdS film and the CdTe film with a SEM, when a measured value of the oxygen atom number ratio exceeds 5000 ppm, a portion where CdS is eroded and missing is partially observed. Was. This is because oxygen atoms contained in the raw material react with Cd of the CdS film to form Cd.
This is considered to be the result of becoming O and eroding the CdS film. CdS
Pinholes were also observed in the CdTe film on the upper part of the missing part, and a decrease in the thickness of the CdTe film was also confirmed.

SnO ₂ / CdT where CdS is missing
e CdS / CdTe at the interface and where there is no CdS erosion
TEM observation of the interface was performed. As a result, SnO ₂ / Cd
There were many places where the CdTe atomic arrangement was irregular near the Te interface, and an orderly atomic arrangement could be confirmed near the CdS / CdTe interface. In addition, the Td of the CdTe film near the pinhole
In EM observations as well, there were many places where CdTe was missing or where the CdTe atomic arrangement was irregular.

From the above, the molar concentration of the oxygen compound determined by the measuring method shown in Example 1 was 5000 ppm.
By using a raw material in the following CdTe powder, Cd
It was found that the interface state between the S film and the CdTe film was improved, and the crystallinity of the CdTe film formed thereon was further improved.

Example 4 Pulverized CdT as a raw material
Six types of CdTe powder samples were prepared by adding a certain amount of Te powder to the e-single crystal and adding Cd powder to the single crystal at varying amounts. As a result of measuring the impurities of these raw materials in the same manner as in Example 1, the atomic ratio of metal Te was 2 in each case.
000 ppm, and the atomic ratio of metal Cd is 10 pp, respectively.
m, 101 ppm, 1015 ppm, 2000 ppm,
4995 ppm and 9996 ppm. Cd in the same manner as in Example 2 except that these raw materials were used.
A Te film was produced.

An X-ray diffraction pattern was measured for each CdTe film produced using each raw material, and a chemical analysis was carried out. As a result, all the films were oriented to the (111) plane, and Cd and Td in the film were determined.
The atomic ratio of e was almost 1: 1. Also, Cd
A cross section near the interface between the S film and the CdTe film was observed by SEM. As a result, when CdTe powder having a lower molar concentration of metal Cd than that of metal Te was used, a portion where CdS was eroded and missing was partially removed. Was observed. This is considered to be the result of the erosion of the CdS film by the metal Te contained in the raw material. On the other hand, when the atomic ratio of metal Cd was equal to or higher than the atomic ratio of Te, no erosion of the CdS film was observed in any case. This is because Cd sublimated at a lower temperature than Te
This is probably because the erosion of the CdS film by e was prevented.

From the above, the CdS film and the CdTe film can be obtained by using a CdTe powder having the atomic ratio of metal Cd obtained by the measuring method shown in Example 1 equal to or greater than the atomic ratio of metal Te. It has been clarified that the interface state between the CdTe film and the CdTe film formed thereon is improved.

Example 5 FIG. 3 shows a cross section of a solar cell manufactured as an example. A CdTe film 13 was formed on the thin film forming substrate shown in Example 2, an aqueous solution of cadmium chloride was coated on the CdTe film 13, dried, and dried.
Heat treatment was performed at 00 ° C. for 30 minutes to grow CdTe grains. Next, on the CdTe film 13, a carbon paste obtained by kneading an organic solvent solution of a resin and carbon powder was applied by screen printing, dried, and baked to form a carbon electrode 14 by baking. Next, the CdTe film 13 around the carbon electrode 14 is scraped with a metal jig to remove CdTe film 13.
The surface of the dS film 12 is exposed, a paste obtained by kneading a silver powder, an indium powder and an organic solvent solution of a resin on the exposed portion and the carbon electrode layer 14 is applied, dried, and the negative electrode 15, and The positive electrode 16 was formed. Example 1 was used as a raw material for the CdTe film.
A to I in which the impurity concentrations measured by the method described in (1) are the values in Table 4.
9 kinds of CdTe powders were used. The conversion efficiency of the manufactured solar cell was measured using a solar simulator, AM 1.5,
It was measured under the condition of 100 mW / cm ² . Table 4 shows the measurement results.

[0054]

[Table 4]

From Table 4, it can be seen that the atomic ratio of metal Te contained in the CdTe powder is 1000 ppm or less and the atomic ratio of oxygen is 5000 ppm or less (samples A, B,
C) shows that the conversion efficiency of the solar cell is high,
e is not more than 1000 ppm, the oxygen compound is not more than 5000 ppm, and the metal Cd
It was confirmed that the conversion efficiency was highest when the atomic ratio of was higher than the ratio of metal Te (sample A). Also,
Even when the atomic ratio of metal Te is 1000 ppm or more, when the atomic ratio of metal Cd is equal to or greater than the atomic ratio of metal Te (samples G and H), the conversion efficiency of the solar cell is relatively high. Was confirmed. For these solar cells, short-circuit current, open-circuit voltage, and fill factor were measured in addition to the conversion efficiency. When the conversion efficiency was good, all other characteristics were good.

Next, of the solar cell of Example 5, metal Te
And the solar cell of the present invention manufactured using the sample (A) having the smallest atomic ratio of oxygen, and the solar cell of the comparative example manufactured using the sample (I) having the highest atomic ratio of metal Te and oxygen. The wavelength dependence of the relative current intensity was measured to compare the spectral sensitivity characteristics of the samples. FIG. 4 shows the results. As shown in FIG. 4, when the sample (A) was used, 500 to 650 n was mainly used as compared with the case where the sample (I) was used.
It can be seen that the relative current intensity is improved in the wavelength range of m. This is because a CdS film and a CdT film are formed by using CdTe powder having a small atomic ratio of metal Te or oxygen.
This is probably because the crystallinity of the CdTe film at the interface of the e film was improved and the number of carriers that could be taken out was increased.

In each of the above embodiments, a tin oxide film is used as the transparent conductive film. However, similar effects can be obtained when another film such as an indium tin oxide film or a zinc oxide film is used.
The CdS film was formed by thermally decomposing cadmium diethyldithiocarbamate. However, the CdS film was formed by other methods such as a method of thermally decomposing other cadmium organic complexes, a liquid phase growth method, a proximity sublimation method, a vapor deposition method, and a sputtering method. The same effect can be obtained when the film is formed.

Further, in Examples 2 to 5, the raw material layer 7 was formed by laying it on the source holder 6, but a solvent was added to the CdTe powder to form a paste, which was applied on a heat-resistant substrate and dried to form a raw material layer. The same effect can be obtained by forming by the method of forming. Furthermore, in Example 5, a CdS / CdTe solar cell was manufactured using a light-transmitting substrate made of borosilicate glass, but another glass substrate such as soda-lime glass or another light-transmitting substrate other than the glass substrate was used. Can also be used. Also, various CdTe-based solar cells using an n-type semiconductor film such as CdZnS other than the CdS film can be manufactured by the same method.

[0059]

According to the present invention, the concentration of trace impurities (metal Te, metal Cd, oxygen compounds, etc.) in CdTe powder can be quantitatively and accurately measured by a simple measuring method. Further, according to this measuring method, the ratio of the number of atoms in each impurity to the total number of atoms in the sample is determined, and CdTe powder whose ratio satisfies a predetermined condition is converted to CdTe by proximity sublimation.
High quality CdTe by using as a material for film formation
A film and a CdTe / CdS solar cell that is inexpensive and has high conversion efficiency can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a triangular diagram in which an atomic concentration ratio of three elements including Cd, Te, and a third element is plotted in the present invention.

FIG. 2 is a longitudinal sectional view showing an arrangement of main members when a CdTe film is formed according to an embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a solar cell according to an example of the present invention.

FIG. 4 is a diagram showing spectral sensitivity characteristics of the solar cell of the present invention and a solar cell of a comparative example.

[Explanation of symbols]

 Reference Signs List 1 Metal Cd region 2 Metal Te region 3 CdTe region 4 Oxygen compound region 6 Source holder 7 Raw material layer 8 Spacer 9 Thin film formation substrate 10 Glass substrate 11 Transparent conductive film 12 CdS film 13 CdTe film 14 Carbon electrode 15 Negative electrode 16 Positive electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G001 AA01 BA04 CA01 FA02 HA01 JA12 JA13 KA01 LA02 MA04 NA03 NA10 NA17 SA12 2G055 AA05 AA09 BA01 CA01 CA25 FA04 5F051 AA09 CB11 KA09

Claims (9)

[Claims] 1. A method for measuring the concentration of a metal cadmium, a metal tellurium, and an impurity comprising a compound containing a third element in a cadmium telluride powder sample, the method comprising the steps of: Cadmium, tellurium determined at each measurement point, and the atomic concentration ratio of the three elements consisting of the third element are plotted on a triangular diagram having the three elements as vertices. The number of measurement points in which the atomic concentration ratio is plotted in a predetermined region unique to each impurity is obtained, and the ratio of the number of measurement points to the total number of measurement points indicates the number of atoms in each impurity with respect to the total number of atoms in the sample. A method for measuring the impurity concentration of cadmium telluride powder, characterized by determining the ratio of cadmium telluride. 2. The method for measuring the impurity concentration of cadmium telluride powder according to claim 1, wherein the third element is oxygen. 3. A region where the atomic concentration ratio between cadmium and tellurium on the triangular diagram is 3/2 or more and the atomic concentration ratio between cadmium and oxygen is 3/2 or more is the predetermined region unique to metal cadmium. A method for measuring the impurity concentration of a cadmium telluride powder according to claim 2. 4. A region where the atomic concentration ratio of cadmium and tellurium on the triangular diagram is 2/3 or less and the atomic concentration ratio of tellurium and oxygen is 3/2 or more is the predetermined region unique to metallic tellurium. A method for measuring the impurity concentration of a cadmium telluride powder according to claim 2. 5. A region where the atomic concentration ratio of cadmium to tellurium on a straight line connecting the vertices of cadmium and tellurium on the triangular diagram exceeds 2/3 and is less than 3/2, A region where the atomic concentration ratio of tellurium is 3/2 or more, the atomic concentration ratio of cadmium and oxygen is 3/2 or more, and the atomic concentration ratio of cadmium and tellurium on the triangular diagram is 2/3 or less, The method for measuring the impurity concentration of cadmium telluride powder according to claim 2, wherein a region excluding three regions of which the atomic concentration ratio of oxygen is 3/2 or more is the predetermined region unique to an oxygen compound. 6. A sample taken from a raw material cadmium telluride powder, the concentration of metal tellurium is measured by the measuring method according to claim 4, wherein the ratio of the number of tellurium atoms to the total number of atoms in the sample is 1000 ppm or less. The raw material cadmium telluride powder is disposed on the source holder,
A method for producing a cadmium telluride film, wherein the raw material cadmium telluride powder is heated and vaporized to form a cadmium telluride film on a thin film forming substrate disposed close to and opposed to the source holder. 7. A sample collected from a raw material cadmium telluride powder, the concentration of the oxygen compound is measured by the measuring method according to claim 5, and the ratio of the number of oxygen atoms in the oxygen compound to the total number of atoms in the sample is measured. A cadmium telluride powder having a content of 5,000 ppm or less is provided on a source holder, and the cadmium telluride powder is heated and vaporized, so that the cadmium telluride powder on the thin film forming substrate is disposed close to and opposed to the source holder. A method for producing a cadmium telluride film, wherein a cadmium telluride film is formed on the substrate. 8. For a sample collected from a raw material cadmium telluride powder, the respective concentrations of metal cadmium and metal tellurium are measured by the measuring method according to claim 3 and 4, and the number of atoms relative to the total number of atoms in all samples is measured. Cadmium telluride powder having a ratio of metal cadmium ≧ metal tellurium is disposed on a source holder, and the raw material cadmium telluride powder is heated and vaporized, so that the source cadmium telluride powder is brought close to and opposed to the source holder. A method for producing a cadmium telluride film, wherein a cadmium telluride film is formed on an arranged thin film forming substrate. 9. A transparent conductive film and a cadmium sulfide film are sequentially formed on a light-transmitting insulating substrate, and a cadmium telluride film is formed on the cadmium sulfide film by the manufacturing method according to claim 6. Formed solar cells.