JP3461620B2 - Method for manufacturing compound semiconductor thin film and method for manufacturing photoelectric conversion element - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor thin film using an organic sulfur cadmium complex and a method for manufacturing a photoelectric conversion element.

[0002]

2. Description of the Related Art CdS films used in optical sensors and optical filters that utilize the change in film resistance due to light irradiation are generally known to be formed by printing coating, sintering, or by a solution deposition method. . However, these methods have a problem that mass production is difficult. Further, at present, a CdS / CdTe solar cell is known as being practically used as a compound semiconductor solar cell using a CdS film. However, the CdS film is formed by forming a CdS paste, printing it, and then sintering the paste. Therefore, the produced CdS film thickness is 20 to
Since the thickness is 50 μm and the film is thick, the light transmittance is limited, and it is difficult to improve the photoelectric conversion efficiency of the photoelectric conversion element. To improve the conversion efficiency, thinning of the CdS film is required. In addition, since CdS / CdTe compound semiconductor photoelectric conversion element uses Cd as a photoelectric conversion element constituent material, when a solar cell, which is a product using the photoelectric conversion element, spreads to general households, a problem of cadmium environmental pollution occurs. have.

Therefore, at present, as one method for minimizing the problem of cadmium environmental pollution, thinning of the CdS film is considered, and development of a practical manufacturing method of the CdS thin film is demanded. As a method for manufacturing a CdS thin film, a vacuum vapor deposition method, a sputtering method, a solution deposition method and the like are known. The vacuum vapor deposition method is a method in which CdS itself is heated and evaporated under a vacuum to form a CdS film on a substrate. In the sputtering method, a voltage is applied between the CdS source and the film formation substrate under a low pressure to generate CdS generated from the CdS source substrate on the film formation substrate. The solution deposition method is a method of dissolving a compound containing Cd and S in a solution to deposit a CdS film on a substrate.

[0004]

However, such a vacuum vapor deposition method and a sputtering method require vacuum equipment, and in order to obtain a large area CdS film, expensive equipment is required. In addition, in the solution deposition method, the CdS film is deposited not only on the required surface of the film formation substrate but also on the back surface, and further, the CdS film is also deposited on components other than these substrates, so the back surface of the film formation substrate is masked. In addition, it is necessary to clean the container and the stirrer for each precipitation treatment, and since the solution itself cannot be regenerated, it is necessary to replace all of them. Thus, it can be said that these conventional methods are not suitable for continuous production or provision of low-cost semiconductor thin films.

The present invention solves such problems and provides a method capable of continuously producing a uniform CdS thin film with an inexpensive apparatus.

[0006]

According to the present invention, an organic sulfur cadmium complex is vaporized, and a CdS producing substrate such as glass heated to the decomposition temperature of the organic sulfur complex is placed in the vapor to form an organic compound on the surface of the CdS producing substrate. In this structure, the sulfur-cadmium complex is decomposed to form a CdS film on the surface of the glass substrate.

[0007]

The CdS thin film can be uniformly formed on the surface of the substrate by placing the substrate in the organic sulfur-cadmium complex vapor and setting the substrate surface temperature to the decomposition temperature of the organic sulfur-cadmium complex or higher. Further, the film thickness of the produced CdS film can be freely controlled from 0.01 μm to 5 μm by suppressing the amount of organic sulfur cadmium complex vapor. Since the obtained CdS film has excellent light transmittance, a conventional CdS film forming method, for example, a CdS paste composed of CdS crystal particles and an organic binder was applied by screen printing, and then the substrate was produced by sintering. 2 more photocurrent than a solar cell using thick film CdS
It can be improved by 0 to 50%. Further, the CdS film can be formed under atmospheric pressure or in an inert gas. further,
It is possible to manufacture a thin film CdS film in a heat plate type belt furnace, and it is also possible to manufacture a large area thin film CdS. Further, in the solar cell element using this thin film CdS photoelectric conversion element, the amount of Cd used in the conventional solar cell element using the thick film CdS can be reduced to about 1/100, which causes the problem of Cd environmental pollution. It is possible to make it extremely small.

[0008]

EXAMPLE FIG. 1 shows the manufacturing process of the organic sulfur cadmium complex of this example. 1 is a glass substrate on the source side,
Reference numeral 2 is an organic sulfur cadmium complex, 3 is a glass substrate on the film forming side, 4 is a vapor of the organic sulfur cadmium complex, and 5 is a formed CdS film. SnO ₂ is used for the glass substrate on the film formation side.
A transparent conductive film formed of a mixture of C and F ₂ was used. As the transparent conductive film, one containing an indium oxide or zinc oxide-based compound may be used, and its conductivity is preferably in the range of 100 Ω / cm ² or less. 1
When it exceeds 00 Ω / cm ² , when the solar cell element is formed, the internal resistance of the solar cell increases, and the photoelectric characteristics deteriorate. As shown in FIG. 1A, an organic sulfur cadmium complex 2 is applied on a source-side glass substrate 1 with a constant film thickness to form a film-forming-side glass substrate 3 and a source-side glass substrate 1.
A spacer 6 is installed between them, and a closed space 7 is created by the spacer 6, the glass substrate 3, and the source-side glass substrate 1. This closed space is preferably an inert gas atmosphere such as N ₂ or Ar, but the presence of some oxygen may cause C
It does not hinder the formation of dS film. Of these three members (the source-side glass substrate 1 coated with the organic sulfur cadmium complex 2, the spacer 6, and the film-forming-side glass substrate 3), the glass substrate is adjusted so that the temperature inside the glass substrate is a temperature at which the cadmium complex melts and vaporizes. 3 is heated, and the heating temperature is set to be equal to or higher than the decomposition temperature of the cadmium complex. Desirably 300-4
00 ℃ is good, and by keeping this state for about 5 minutes, organic sulfur cadmium complex vapor is decomposed on the surface of the film formation side glass substrate, and a thin film of cadmium sulfide (CdS) suitable for photoelectric conversion element is deposited. Can be done.

An embodiment of the present invention will be described below. Example 1 An example in which a cadmium diethyldithiocarbamate complex is used as the organic sulfur cadmium complex 2 will be described. The decomposition temperature of the complex is 250 to 350.
CdS film formation substrate temperature is set to the decomposition temperature of this complex or higher (here, 350 ° C.), and the glass substrate temperature on the source supply side is the melting point of the cadmium diethyldithiocarbamate complex (240 ° C.). ) And the decomposition temperature (300 to 350 ° C.).
In the structure shown in FIG. 1, the temperature of the glass substrate 1 on the source supply side is about 100 times higher than the temperature of the glass substrate 3 on the film formation side.
The temperature of the glass substrate 1 on the source supply side becomes 200 ° C.
The temperature was controlled in the range of ℃ to 300 ℃. As a result, as shown in FIG. 1B, the diethyldithiocarbamate cadmium complex applied to the surface of the source supply substrate was melted and vaporized, and the diethyldithiocarbamate cadmium was stored in the closed space 7 which was previously replaced with an N ₂ atmosphere. The complex vapor fills. As shown in (c), the diethyldithiocarbamate cadmium complex vapor was decomposed on the surface of the CdS film forming substrate, and the CdS film could be formed.

The optical characteristics of the obtained CdS film are shown in FIG. In the figure, for comparison, the characteristics of the CdS film prepared by the conventional manufacturing method of screen-printing and then sintering are also shown. As can be seen from these results, C prepared by the present invention
The dS film exceeds the spectral transmittance of the CdS film formed by the conventional screen printing and sintering methods in the entire light transmission wavelength range,
Since it is a thin film, it has optical transparency even in a short wavelength region of 500 nm or less. Therefore, it was revealed that the CdS film produced according to the present invention is a film having optically superior characteristics as compared with the conventional CdS film.

Example 2 A cadmium diethyldithiocarbamate complex was coated on the substrate 1 and the temperature of the substrate 1 was adjusted to
The temperature of the glass substrate 3 on the film formation side was set to 350 ° C. by controlling at 250 ° C. The temperature holding time was 5 minutes. A film thickness of 100Å was obtained in 3 minutes and 10,000Å in 10 minutes.

The CdS film thickness affects the photoelectric characteristics, but the light transmittance increases as the film thickness decreases. However, it was found that the open circuit voltage Voc becomes unstable. The preferable CdS film thickness is in the range of 100 to 10000Å, and the optimum photoelectric property of the photoelectric conversion element is shown.

In Example 2, various film thicknesses were obtained by forming the CdS film by keeping the temperature of the glass substrate on the film forming side constant and changing the heating time. In this example, the glass substrate on the film forming side was obtained. Various CdS film thicknesses were obtained by changing the temperature and keeping the heating time at that time constant. Both films showed almost the same optical characteristics as in Example 1.

In producing the CdS films of Examples 1 and 2,
Is the closed space in FIG. 1- (a) is N ₂Replace with gas in advance
Then, a CdS film was produced. This CdS film formation process
Should preferably be performed in an inert gas atmosphere.
When this is done in an oxygen atmosphere, CdS reacts with oxygen,
The light transmittance of the CdS film is low due to the generation of CdO.
Because I will give you down. However, even if the oxygen concentration is low
Therefore, such a problem does not occur.

[0015] In this embodiment, the O ₂ gas in addition to the N ₂ gas was performed to create a CdS film with N ₂ / O ₂ gas atmosphere.
The relationship between the light transmittance of the obtained film and the concentration of the N ₂ / O ₂ gas used is shown in FIG. As can be seen from the figure, the presence of 10% or less of O ₂ does not impair the intended CdS film properties.

Example 3 A photoelectric conversion element using the CdS film produced in Example 1 was produced. A schematic sectional view of the device is shown in FIG. In the figure, 9 is a CdTe film, 10 is a C electrode film, and 11 is an AgIn electrode film. On the CdS film 5 prepared in Example 1, P is mixed powder of Cd, Te and CdTe.
A paste made of HG (phenyl glycol) was applied by a screen printing method, and this substrate was sintered at a temperature of 660 ° C. in a nitrogen gas atmosphere. Formed C
A carbon paste is further applied onto the dTe film 9 to form 400
The carbon electrode 10 was formed on the CdTe film by drying and curing at a temperature of ℃. Furthermore, as an electrode of the CdS film 5,
The AgIn paste was applied on the CdS film and dried and hardened at 200 ° C. to form the AgIn electrode 11.

The thin film CdS produced by the present invention is C
When the dTe film 9 is formed, the thin film CdS formed by various thin film forming methods such as the solution deposition method, the sputtering method, and the vapor deposition method is
While CdTe erodes a film thickness of about 3000 Å, it has the property of eroding only about 500 Å.
Therefore, the photoelectric conversion element can be prepared even if the film thickness of CdS is as thin as 500 to 1000Å, and the photoelectric flow rate can be increased.

The compound semiconductor photoelectric conversion device of the thin film CdS thus produced has a resistance of 100 mW / cm ² , AM
Under the condition of 1.5, a short circuit current value of 24 mA / cm ² and an open circuit voltage of 0.8 V / cell were obtained.

(Comparative Example 1) The effect of Example 3 was examined.
Therefore, the CdS film and CdTe film are formed by the screen printing method.
CdS compound semiconductor optical conversion device based on conventional method
Was prepared and its characteristics were measured under the same conditions as in Example 5.
As a result, the short-circuit current was 19 mA / cm ²Got
The open circuit voltage was 0.75 V / cell.

As can be seen from the above comparative examples, 100 mW
In the conventional thick film CdS method, the short-circuit current is 19 mA / cm ² under the conditions of AM / cm ² and AM1.5 of 24.
mA / cm ² was obtained, and an improvement in the short circuit current value of 20% was recognized. In addition, since the pn junction layer serving as the electromotive force generation layer can be made uniform, the open circuit voltage is the same as the conventional thick film
Whereas the dS photoelectric conversion element is 0.75V / cell,
The thin film CdS photoelectric conversion element was able to obtain a high voltage of 0.80 V / cell. Also, as the intrinsic photoelectric conversion efficiency,
13% was obtained compared to 11% for the conventional thick film.

(Embodiment 4) In this embodiment, Embodiments 1 to 3 are used.
A CdS film was prepared by replacing the cadmium diethyldithiocarbamate used as the organic sulfur cadmium complex in 1. with an imidazole cadmium complex. A 2-mercaptobenzimidazole Cd complex was used as the imidazole cadmium complex used.

The decomposition temperature of this complex is 300 ° C to 350 ° C.
CdS film formation substrate temperature is set above this decomposition temperature, and the glass substrate temperature on the source supply side is the melting point (250 to 280 ° C.) and decomposition temperature (300 to 400 ° C.) of the imidazole cadmium complex. Set to range. Thus, on the thin film CdS5 formed in the same manner as in Example 1, the CdTe films 9 and C were formed based on the method shown in Example 5.
The film 10 and the AgIn film 11 were formed to prepare a photoelectric conversion element. The photoelectric characteristics of the obtained device are almost the same as those of the device obtained in Example 3.

Similar results were obtained when a cadmium diethyldithiocarbamate complex and an imidazole cadmium complex were mixed and used.

Example 5 In this example, a photoelectric conversion element was prepared in the same manner as in Example 3 except that a mercaptobenzocadmium complex was used as the organic sulfur cadmium complex. The photoelectric characteristics of the obtained device were almost the same as those of the device obtained in Example 3.

[0025]

As is clear from the above description, the compound semiconductor thin film and the photoelectric conversion device using the same according to the manufacturing method of the present invention in which a CdS film is formed on a glass substrate using an organic sulfur cadmium complex, The light transmittance was 20 to 50% higher than that of the conventional thick film CdS. Further, it was confirmed that the light transmittance was about 10% higher than that of the solution deposition method, the sputtering method, and the vapor deposition method with the same film thickness, and it was found that an excellent photoelectric conversion element can be provided.

The method for producing a CdS film according to the present invention is 5
Since the CdS film can be formed in an extremely short time of 10 minutes and can be applied to the production of CdS in a large area, it is a manufacturing method with extremely excellent productivity. The light transmittance of the thin film CdS of the present invention is observed to be 20 to 50% higher than the light transmittance of the conventional thick film CdS, and the photoelectric characteristics of the photoelectric conversion element are 100 mW / cm ² and irradiation light of AM1.5. in short circuit current is increased from 19 mA / cm ² to 24mA / cm ^2.

Further, C contained in the created photoelectric conversion element
Since the thin film CdS having a d content of 100 to 1000 Å is used, the content of Cd in the device is about 1 of that of the conventional thick film CdS.
/ 200 to 1/2000, and the degree of the environmental pollution problem was significantly reduced.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a CdS film according to an embodiment of the present invention.

FIG. 2 is a diagram showing spectral sensitivity characteristics of a CdS film according to an embodiment of the present invention and a CdS film formed based on a conventional method.

FIG. 3 is an atmosphere gas O ₂ / which forms a CdS film using an organic sulfur cadmium complex according to an embodiment of the present invention.
Shows the spectral sensitivity characteristics of CdS film was produced with N ₂ ratio

FIG. 4 is a sectional structural view of a photoelectric conversion element according to an embodiment of the present invention.

[Explanation of symbols]

1 Source side glass substrate 2 Organic sulfur cadmium complex 3 Film formation glass substrate 4 Organic Sulfur Cadmium Complex Vapor 5 CdS film 6 spacers 7 closed space 8 CdTe film

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Kondo 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-8-88382 (JP, A) JP-A-61- 166978 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/365 H01L 31/04 H01L 31/0248

Claims (5)

(57) [Claims] 1. A vapor of an organic sulfur-cadmium complex containing at least sulfur, nitrogen, carbon and cadmium atoms is generated, and the complex is thermally decomposed on the surface of the substrate placed in the complex vapor, and CdS is formed on the surface of the substrate. A method for producing a compound semiconductor thin film, which comprises forming a thin film. 2. The method for producing a compound semiconductor thin film according to claim 1, wherein the CdS thin film is formed in at least an N ₂ atmosphere or an atmosphere containing O ₂ . 3. The method for producing a compound semiconductor thin film according to claim 1, wherein the organic sulfur cadmium complex includes at least one kind of an imidazole cadmium complex, a thiazole cadmium complex, and a cadmium carbamate complex. 4. An organic sulfur cadmium complex is melted and vaporized within a temperature range from the melting point to the decomposition temperature of the complex, and the surface temperature of the substrate placed in the vapor of the complex is set to the decomposition temperature of the complex or higher. The method for producing a compound semiconductor thin film according to claim 1, 2 or 3, wherein the organic sulfur cadmium complex is thermally decomposed on the substrate surface to form a CdS thin film on the substrate surface. 5. Cd, Te and CdTe on a CdS thin film produced by the method of claim 1, 2, 3 or 4.
A method of manufacturing a photoelectric conversion element, which comprises applying a paste containing one or more compounds selected from the above and sintering it to form a CdTe film.