WO2001026161A1

WO2001026161A1 - Compound semiconductor solar cell and method of manufacture thereof

Info

Publication number: WO2001026161A1
Application number: PCT/JP2000/006932
Authority: WO
Inventors: Tetsuya Aramoto; Hideaki Oyama; Miwa Tsuji; Palaniappagounder Veluchamy; Tsuyoshi Nishio
Original assignee: Matsushita Battery Industrial Co., Ltd.
Priority date: 1999-10-05
Filing date: 2000-10-04
Publication date: 2001-04-12

Abstract

A compound semiconductor solar cell comprises a transparent substrate, a transparent electrode layer consisting of an impurity-containing metal oxide formed on the transparent substrate, an n-type compound semiconductor layer formed on the transparent electrode layer, and a p-type compound semiconductor layer formed on the n-type compound semiconductor layer. The transparent electrode layer has a high impurity concentration toward the transparent substrate and a low impurity concentration toward the n-type compound semiconductor layer.

Description

Description Compound semiconductor solar cell and method of manufacturing the same

The present invention relates to a compound semiconductor solar cell and a method for manufacturing the same. Background art

Solar cells, which convert light energy into electrical energy, can use the inexhaustible energy of sunlight. Solar power is a clean energy source, unlike fossil fuels. Therefore, solar cells have been actively applied to electronic devices such as various optical sensors. Among them, compound semiconductor solar cells can be expected to have high conversion efficiency because of their large absorption coefficient.

A compound semiconductor solar cell generally includes a transparent electrode layer formed on a transparent substrate such as a glass substrate, an n-type compound semiconductor layer formed thereon, and a P-type compound semiconductor layer formed thereon. Have been.

The transparent electrode layer is generally made of a metal oxide, and contains an impurity as a carrier for increasing conductivity. The impurity concentration in the transparent electrode layer is preferably high on the transparent substrate side from the viewpoint of sheet resistance, and low on the n-type compound semiconductor layer side from the viewpoint of carrier mobility.

However, the transparent electrode layer is formed on the substrate by a method such as evaporation using a raw material containing impurities as carriers. Therefore, there is a problem that the impurity concentration in the conventional transparent electrode layer becomes uniform.

When an n-type compound semiconductor layer is formed directly on a transparent electrode layer, the n-type compound semiconductor layer is formed under the influence of the surface condition of the underlying transparent electrode layer. And its strength decreases There is also a problem. At the interface between the weak n-type compound semiconductor layer and the p-type compound semiconductor layer, a mixed crystal layer composed of the constituent elements of both layers is likely to be formed. Disclosure of the invention that the mixed crystal layer lowers the performance of the Pn junction and lowers the open-circuit voltage of the solar cell.

The present invention provides a transparent substrate, a transparent electrode layer made of a metal oxide containing impurities formed on the transparent substrate, an n-type compound semiconductor layer formed on the transparent electrode layer, and a n-type compound semiconductor layer formed on the n-type compound semiconductor layer. A compound semiconductor solar cell comprising the formed p-type compound semiconductor layer, wherein the impurity concentration in the transparent electrode layer is high on the transparent substrate side and low on the n-type compound semiconductor layer side. To a compound semiconductor solar cell.

The transparent electrode layer is preferably made of tin oxide containing a halogen element as an impurity.

The transparent electrode layer includes a first metal oxide layer on the transparent substrate side and a second metal oxide layer on the n-type compound semiconductor layer side, and the first metal oxide layer has an impurity concentration of the second metal oxide layer. It is preferably higher than the impurity concentration in the metal oxide layer.

A ratio of the thickness of the second metal oxide layer to the thickness of the first metal oxide layer is 0.02 to 0.7, and the ratio of the second metal oxide layer to the impurity concentration in the first metal oxide layer is The ratio of the impurity concentration in the metal oxide layer is preferably 0.5 or less.

The solar cell of the present invention has a thickness of 10 angstroms or more between the transparent electrode layer and the n-type compound semiconductor layer, and includes a constituent element of the transparent electrode layer and the n-type compound semiconductor layer. It is preferable to have a mixed crystal layer.

The transparent electrode layer is made of tin oxide containing a halogen element as an impurity. It is preferable that the n-type compound semiconductor layer is made of a metal sulfide, and the mixed crystal layer is made of tin, cadmium, sulfur, and oxygen.

The mixed crystal layer preferably contains chlorine.

The present invention also relates to a method for manufacturing a compound semiconductor solar cell according to any of the above.

That is, the present invention provides a step of forming a metal oxide layer containing impurities on a transparent substrate, and heating the metal oxide layer in a reducing atmosphere to thereby reduce the impurity concentration in the metal oxide layer. The present invention relates to a method for manufacturing a compound semiconductor solar cell, comprising: a step of increasing the thickness on the substrate side and decreasing the level on the surface side;

In the present invention, the step of forming the first metal oxide layer containing impurities on the transparent substrate may further include: forming a first metal oxide layer containing impurities at a lower concentration than the first metal oxide layer on the first metal oxide layer. The present invention relates to a method for manufacturing a compound semiconductor solar cell having a step of forming a two-metal oxide layer.

In this case, the temperature of the transparent substrate can be temporarily lowered to room temperature after the formation of the first metal oxide layer and before the formation of the second metal oxide layer. However, after the formation of the first metal oxide layer, the second metal oxide layer is preferably formed without lowering the temperature of the transparent substrate.

The present invention includes a step of forming a metal oxide layer containing impurities on a transparent substrate, and a step of forming an n-type compound semiconductor layer on the metal oxide layer in an atmosphere containing a raw material of the metal oxide. The present invention relates to a method for manufacturing a compound semiconductor solar cell. In the latter step, a mixed crystal layer composed of constituent elements of both layers is formed between the metal oxide layer and the n-type compound semiconductor layer, and an impurity concentration lower than the impurity concentration on the metal oxide layer. Is formed.

In this case, a liquid comprising the metal oxide raw material and a solvent or a dispersion medium is used. It is preferable to obtain the atmosphere by vaporizing or atomizing. The raw material of the metal oxide is preferably made of a halide containing at least tin or zinc. The halide is preferably dimethyltin dichloride or methyl zinc chloride.

The present invention provides a step of forming a metal oxide layer containing impurities on a transparent substrate, and applying the raw material of the metal oxide on the metal oxide layer, and then forming an n-type compound on the metal oxide layer. The present invention relates to a method for manufacturing a semiconductor solar cell having a step of forming a semiconductor layer. In the latter step, a mixed crystal layer and a second metal oxide layer are formed as described above.

In this case, the raw material of the metal oxide is preferably made of a halide containing at least tin or zinc.

The present invention provides a step of forming a metal oxide layer containing impurities on a transparent substrate, using a mixture of the metal oxide raw material and the n-type compound semiconductor raw material on the n-type compound semiconductor on the metal oxide layer. The present invention relates to a method for manufacturing a compound semiconductor solar cell having a step of forming a layer. In the latter step, a mixed crystal layer and a second metal oxide layer are formed as described above.

In this case, it is preferable that the raw material of the metal oxide is made of a halide containing at least tin or zinc. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing the relationship between the secondary ion intensity obtained when the transparent electrode layer in contact with the sulfur-doping layer of Example 1 was analyzed by SIMS and the measurement cycle.

FIG. 2 is a scanning electron micrograph showing a cross section of the transparent electrode layer of Example 1.

FIG. 3 is a diagram showing the distribution of the open circuit voltage of the solar cell obtained in Example 1. You.

FIG. 4 is a diagram showing the distribution of the fill factor of the solar cell obtained in Example 1.

FIG. 5 is a diagram showing a current density distribution of the solar cell obtained in Example 1.

FIG. 6 is a diagram showing the distribution of the conversion efficiency of the solar cell obtained in Example 1.

Figure 7 shows the photoelectron intensity of each element obtained when a sample consisting of a tin oxide layer, a cadmium sulfide layer, and a mixed crystal layer interposed between the two layers was analyzed by Auger electron spectroscopy and the photoelectron intensity from the sample surface. FIG. 8 shows the relationship between the depth and the photoelectron intensity obtained when the mixed crystal layer interposed between the tin oxide layer and the sulfur-doping layer was analyzed by Auger electron spectroscopy. FIG. 4 is a diagram showing a relationship with the energy.

FIG. 9 is a transmission electron micrograph showing a cross section of a mixed crystal layer existing between the tin oxide layer and the sulfur-doping layer in Example 4.

FIG. 10 is a diagram showing the distribution of the open-circuit voltage of the solar cell obtained in Example 4.

FIG. 11 is a diagram showing the distribution of the fill factor of the solar cell obtained in Example 4.

FIG. 12 is a diagram showing a current density distribution of the solar cell obtained in Example 4.

FIG. 13 is a diagram showing the distribution of the conversion efficiency of the solar cell obtained in Example 4.

FIG. 14 is a diagram showing the distribution of the open circuit voltage of the conventional solar cell obtained in Comparative Example 1.

Figure 15 shows the distribution of the fill factor of the conventional solar cell obtained in Comparative Example 1. FIG.

FIG. 16 is a diagram showing a current density distribution of the conventional solar cell obtained in Comparative Example 1.

FIG. 17 is a diagram showing the distribution of the conversion efficiency of the conventional solar cell obtained in Comparative Example 1. BEST MODE FOR CARRYING OUT THE INVENTION

The transparent electrode layer of a compound semiconductor solar cell of the present invention, transparency, from the viewpoint of conductivity, S N_〇, tin oxides such as S N_〇 _2, indium tin oxide, I Njiumu, Z n O, C dln ₂ 〇 ₄ , C d S n〇 ₄ , C d〇,

C d 2 S n O 2, Z n 2 S N_〇 _4, I n ₂ O ₃ - is preferably made of a metal oxide such as Z n O.

Among these metal oxides, from the viewpoint of chromatic higher optical transparency and low resistance, tin oxide, indium oxide, indium tin oxide, Z n O, C d I n 2 0 4, C d S n C It is preferable to use such as.

The thickness of the transparent electrode layer is 0.1 to 1 m from the viewpoint of light transmission, and more preferably, 0.:! It is preferably from 0.6 to 0.6 m.

The transparent electrode layer contains an impurity. Impurities are components used to adjust the carrier concentration of the transparent electrode layer. The impurities are selected according to the type of metal oxide.

As the impurities of the tin oxide, for example, a halogen element such as fluorine, chlorine, and bromine, and antimony are preferable. Of these, halogen elements, especially fluorine, are preferred because of their low activation energy. As the impurity of Zn, for example, a group III element In, Al, B, F, Ga and a group 4 element Si are preferable.

More specifically, the transparent electrode layer has higher light transmission and lower resistance. In view of the above, it is preferable to use, for example, indium oxide, indium tin oxide, tin oxide containing halogen element or antimony as an impurity, or ZnO containing In, A 1, or Si as an impurity. In particular, in order to obtain a solar cell having optimal electric characteristics, the transparent electrode layer is preferably a tin oxide containing an octalogene element, particularly fluorine as an impurity. As the n-type compound semiconductor layer, For example, sulfurizing domes,

CdZnS or the like is used. Among these, sulfur doping is particularly preferable in that a solar cell having excellent conversion efficiency can be obtained.

As the P-type compound semiconductor layer, for example,

(C d T e), C u I n S e ₂ , C u I n S ₂ C u I n T e ₂ ,

C u A 1 S e 2, C u A l S 2, C uA l T e 2, C u G a S e 2,

C u G a S 2, C u G a T various Karukoparai DOO compound semiconductor such as e ₂ is used. Of these, tellurium dome is particularly preferable because it has a band gap suitable for absorbing sunlight. Embodiment 1

The transparent electrode layer comprises a first metal oxide layer on the transparent substrate side and a second metal oxide layer on the n-type compound semiconductor layer side, and the impurity concentration in the first metal oxide layer is A compound semiconductor solar cell having a higher impurity concentration in the layer will be described.

When the impurity concentration in the second metal oxide layer on the side of the n-type compound semiconductor layer is reduced, the mobility of carriers in the transparent electrode layer is increased, and the sheet resistance is reduced. Diffusion of impurities into the n-type compound semiconductor layer is also suppressed, and a decrease in the strength of the n-type compound semiconductor layer can be prevented.

One or more metal oxide layers may be further provided between the first metal oxide layer and the second metal oxide layer. However, the metal oxide that constitutes the transparent electrode layer The number of layers is preferably three or less, and most preferably two, from the viewpoint of manufacturing cost and light transmittance.

The thickness of each metal oxide layer is preferably in the range of 0.3 :! to 0.6 m from the viewpoint of the manufacturing process and the light transmittance.

The ratio of the thickness of the second metal oxide layer to the thickness of the first metal oxide layer is preferably from 0.02 to 0.7, and more preferably from 0.4 to 0.6. If this ratio is less than 0.02, the mobility of carriers decreases, and if it exceeds 0.7, the resistance of the transparent electrode layer increases.

The impurity concentration in the first metal oxide layer is preferably 1 ^× 10 ² ^fl to 5 ^× 10 ² ° ^atoms Z cm ³ . The impurity concentration in the second metal oxide layer is preferably 5 × 10 ¹⁹ to ^2.5 × 10 ² ° atoms Z cm ³ . When the impurity concentration in the first metal oxide layer is out of the above range, the carrier mobility decreases, and when the impurity concentration in the second metal oxide layer is out of the above range, the resistance of the transparent electrode layer increases.

The ratio of the impurity concentration in the second metal oxide layer to the impurity concentration in the first metal oxide layer is preferably 0.5 or less, more preferably 0.1 to 0.5. When the ratio exceeds 0.5, the mobility of carriers decreases, and when the ratio is less than 0.1, the resistance of the transparent electrode layer increases.

The impurity concentration may be determined by secondary ion mass spectrometry (SIMS).

According to SIMS, it is possible to know a change in the distribution state of elements in the thickness direction of the transparent electrode layer. The ratio of the impurity concentration in the second metal oxide layer to the impurity concentration in the first metal oxide layer is obtained, for example, as the ratio of the secondary ion intensity at the center in the thickness direction of each metal oxide layer.

Next, an example of a method for forming a transparent electrode layer including the first metal oxide layer on the transparent substrate side and the second metal oxide layer on the n-type compound semiconductor layer side will be described.

(i) First metal oxide layer Raw materials for metal oxides include, for example, tin halides such as dimethyltin dichloride and tin tetrachloride, alkyltin halides such as trimethyltin chloride, tin carboxylates, tin 3-diketone complexes, and tin alkoxides. Can be used. Of these, dimethyltin dichloride is most preferred.

As a raw material for the impurities, for example, fluorides such as ammonium fluoride and sodium fluoride, and antimony compounds such as antimony chloride are used. A raw material liquid is prepared by mixing a metal oxide and a raw material for impurities with water or a solvent such as toluene or dispersed soot.

The ultrasonic vibrator is put in the raw material liquid, and it is operated to atomize the raw material liquid. When the atomized raw material liquid comes into contact with or approaches the surface of the heated transparent substrate, the solvent and dispersed soot evaporate and the raw material is thermally decomposed. As a result, a metal oxide layer containing impurities is formed on the surface of the transparent substrate.

When atomizing the raw material liquid, the raw material liquid may be sprayed. Further, instead of atomizing the raw material liquid, the raw material liquid may be heated and vaporized.

The temperature of the transparent substrate needs to be set to a temperature at which the solvent or dispersion medium in the atomized raw material liquid evaporates and the raw material of metal oxides and impurities is thermally decomposed. Therefore, the temperature of the transparent substrate varies depending on the type of raw material.

In the case of dimethyltin dichloride, the temperature of the transparent substrate is set at 300 to 600 ° C, preferably at 300 to 580 ° C. At a temperature lower than 300 ° C., the thermal decomposition of dimethyltin dichloride is slowed down, it takes time to form a tin oxide layer, and the sheet resistance increases. On the other hand, when the temperature exceeds 600 ° C, the transparent substrate is deformed, or the crystal particle diameter of tin oxide becomes large, which disturbs incident light having an uneven thickness and large irregularities on the surface. It becomes an easy tin oxide layer. To obtain a solar cell with high conversion efficiency, the resistance of the first metal oxide layer must be

It is preferably 20 Ω / port or less. The thickness of the tin oxide layer is preferably from 0.1 to 0.5 m. (ii) Second metal oxide layer

In order to obtain a solar cell with high conversion efficiency, a second metal oxide layer having a higher resistance than the first metal oxide layer is formed. For example, the second metal oxide layer may be formed in the same manner as described above using a raw material liquid containing no impurities. Since some of the impurities in the first metal oxide layer diffuse into the second metal oxide layer, the second metal oxide layer also contains low-concentration impurities. The thickness of the second tin oxide layer is preferably from 0.01 to 0.2 m.

When producing a transparent electrode layer composed of three or more metal oxide layers, the amount of impurities in the raw material liquid and the thickness of the metal oxide layer are controlled to form the first metal oxide layer, The operation may be repeated as many times as necessary, and finally the second metal oxide layer may be formed.

The second metal oxide layer may be formed separately or continuously after the formation of the first metal oxide layer.

Specifically, when there is only one device for forming the metal oxide layer or only one nozzle for introducing the raw material into the device, the first metal oxide layer is formed, and then the second metal oxide layer is formed. Before introducing the raw material into the apparatus, the substrate temperature may be once returned to room temperature. However, once the substrate temperature is returned to room temperature, time loss increases and stress is applied to the transparent substrate due to a temperature change, so that the characteristics of the transparent electrode layer may vary.

On the other hand, a nozzle for introducing the raw material for the first metal oxide layer and a nozzle for introducing the raw material for the second metal oxide layer are installed in the apparatus, and each metal base is successively connected stepwise so that the raw materials are not mixed. When forming an oxide layer, there is no need to lower the substrate temperature, so there is no time loss and no stress is applied to the transparent substrate, Embodiment 2. After forming a metal oxide layer containing impurities on a transparent substrate, the metal oxide layer is heated in a reducing atmosphere, so that the impurity concentration is higher on the transparent substrate side and lower on the n-type compound semiconductor layer side. A method for obtaining the following will be described. The metal oxide layer containing impurities may be formed in a manner similar to that of the first metal oxide layer in Embodiment 1. Then, the metal oxide layer is heated in a reducing atmosphere to desorb impurities near its surface.

As the reducing atmosphere, a nitrogen atmosphere having an oxygen concentration of 30 ppm or less is preferable. If the oxygen concentration exceeds 30 ppm, no impurities are eliminated from the metal oxide layer. The heating temperature is preferably from 500 to 600 ° C. If the temperature is lower than 500 ° C., impurities do not desorb from the metal oxide layer, and if the temperature exceeds 600 ° C., the physical properties of the metal oxide change or the crystallinity decreases, and the light transmission of the metal oxide decreases. Or decrease in sex. In order to efficiently remove impurities from the metal oxide layer, it is more preferable to set the heating temperature to 530 ° C. or higher. Embodiment 3

The solar cell according to the present embodiment has the same transparent electrode layer as in Embodiment 1 or 2, and further includes a transparent electrode layer and an n-type compound semiconductor layer between the transparent electrode layer and the n-type compound semiconductor layer. It has a mixed crystal layer (mixed layer) composed of elements. The mixed crystal layer is composed of the constituent elements of the transparent electrode layer and the n-type compound semiconductor layer, and has different physical properties from both the transparent electrode layer and the n-type compound semiconductor layer.

When there is a mixed crystal layer, the n-type compound semiconductor layer is less susceptible to the surface condition of the underlying transparent electrode layer, particularly during its formation. Then, a strong n-type compound semiconductor layer in which elements are arranged in an orderly manner is obtained.

When the transparent electrode layer is made of tin oxide and the n-type compound semiconductor layer is made of sulfide dominate, the mixed crystal layer includes, for example, tin, cadmium, sulfur, and oxygen. It preferably comprises Further, the mixed crystal layer preferably contains chlorine in order to suppress an increase in resistance.

The thickness of the mixed crystal layer is preferably 10 to 100 angstroms. When the thickness of the mixed crystal layer is less than 100 angstroms, the effect of the surface state of the transparent electrode layer on the n-type compound semiconductor layer cannot be sufficiently suppressed, and when the thickness exceeds 100 angstroms, the sheet resistance of the solar cell increases. Will be higher.

Since the transparent electrode layer has a strong surface, no mixed crystal layer is formed even if an n-type compound semiconductor layer is formed on the transparent electrode layer. Even if a mixed crystal layer is formed, its thickness is considered to be less than 10 angstroms. As an example, a method for producing a mixed crystal layer composed of tin, cadmium, sulfur and oxygen will be described.

First, a stock solution containing tin, cadmium and sulfur and a solvent or a dispersion medium is prepared. The raw material liquid may contain, for example, CdSnS. Further, a raw material liquid may be prepared by mixing a tin compound and a compound containing cadmium and sulfur.

Examples of the tin compound include dimethyltin dichloride, trimethyltin chloride, tin tetrachloride, tin carboxylate, tin 3-diketone complex, and tin alkoxide.

Examples of the compound containing force domium and sulfur include cadmium gentium rutile cadmium, cadmium dimethyl dithirubinate, cadmium dibutyl dithiocarbamate, and cadmium dibutyl dithioxanthate.

Using the obtained raw material liquid, a mixed crystal layer can be formed in the same manner as the metal oxide layer. For example, an ultrasonic vibrator is put in a raw material liquid, and this is operated to atomize the raw material liquid. When the atomized raw material liquid contacts or approaches the heated surface of the transparent electrode layer, the solvent or dispersion medium evaporates and the raw material is evaporated. Decomposes thermally. As a result, a mixed crystal layer composed of tin, cadmium, sulfur and oxygen is formed on the surface of the transparent electrode layer.

The temperature of the transparent electrode layer is preferably from 300 to 600 ° C, more preferably from 300 to 580 ° C, for example, when the raw material liquid contains dimethyltin dichloride. Below 300 ° C, thermal decomposition of dimethyltin dichloride slows down and no mixed crystal layer is formed. On the other hand, when the temperature exceeds 600 ° C., the transparent substrate is deformed, the crystal grain size of the mixed crystal layer is increased, and large irregularities are formed on the surface of the mixed crystal layer. As a result, when a cadmium sulfide layer is formed on the mixed crystal layer, the number of defects in the cadmium sulfide layer increases.

The mixed crystal layer can also be formed simultaneously with the formation of the first metal oxide layer containing impurities and then with the formation of the second metal oxide layer and the n-type compound semiconductor layer. To do so, you can do one of the following three steps.

(i) forming an n-type compound semiconductor layer on the first metal oxide layer in an atmosphere containing a raw material of the second metal oxide;

(ii) a step of applying a raw material of a second metal oxide on the first metal oxide layer, and thereafter forming an n-type compound semiconductor layer.

(iii) a step of forming an n-type compound semiconductor layer on the first metal oxide layer using a mixture of a raw material of the second metal oxide and a raw material of the n-type compound semiconductor. Hereinafter, steps (i) to (iii) will be described by taking as an example a case where a CdS layer is formed as an n-type compound semiconductor layer. Itinerary (i)

As a raw material of the second metal oxide layer, for example, octalogenide is used. Examples of the halide include dimethyltin dichloride, tin tetrachloride, trimethyltin chloride, methyl zinc chloride, ammonium fluoride, and sodium fluoride. Of these, dimethyltin dichloride, trimethyltin chloride, Methyl zinc chloride is preferred. A raw material liquid 1 is prepared by mixing a raw material for the second metal oxide layer with a solvent or a dispersion medium such as water or toluene.

Raw materials for CdS include, for example, power dome such as getyl dithiol rubamic acid cadmium, dimethyl dithiocarbamate cadmium, dibutyl dithiocarbamate cadmium, and getyl dithioxanthate cadmium. A compound containing sulfur is used. The CdS raw material is mixed with a solvent such as water or toluene or a dispersed soot to prepare a raw material liquid 2.

First, the raw material liquid 1 is atomized using an ultrasonic vibrator, and then a heated transparent substrate having a transparent electrode layer is introduced under an atmosphere filled with the fine particles of the raw material liquid 1. Subsequently, the raw material liquid 2 is atomized by using an ultrasonic vibrator to form a C d S layer. When atomizing the raw material liquid, the raw material liquid may be sprayed. Further, the raw material liquid may be heated to be vaporized.

The temperature of the transparent substrate depends on the type of raw material. For example, when dimethyltin dichloride is used as a raw material for the second metal oxide layer and cadmium getyldithiocarbamate is used as a raw material for the CdS layer, it may be 400 to 500 :, or even 4300. ~ 500 ° C is preferred. When the substrate temperature is lower than 400 ° C., thermal decomposition of the raw material is unlikely to occur, and many unreacted substances are mixed as impurities into the metal oxide layer. On the other hand, when the temperature exceeds 500 ° C., the metal oxide sublimes or evaporates, so that the second metal oxide layer is not formed or the thickness of the layer becomes uneven. Travel (i i)

As a method of applying a raw material of the second metal oxide on the first metal oxide layer, a method of immersing a transparent substrate having the first metal oxide layer in a raw material liquid of the second metal oxide, A method of printing a second metal oxide raw material liquid on the surface of a transparent substrate having an oxide layer, for example, screen printing, on the first metal oxide layer In addition, there are a method of spraying a raw material liquid of the second metal oxide, a method of atomizing the raw material liquid and attaching it to the surface of the transparent substrate having the first metal oxide layer. Next, a CdS layer is formed on the first metal oxide layer after the material liquid of the second metal oxide is applied. The C d S layer may be formed in the same manner as in the step (i). Process (iii)

First, a raw material liquid containing the same raw material for the second metal oxide layer and the raw material for the CdS layer as used in step (i) is prepared. As this raw material liquid, for example, a mixture of the raw material liquid 1 and the raw material liquid 2 in step (i) can be used. The raw material of the second metal oxide layer and the raw material of the CdS layer are mixed, for example, such that the molar ratio between the metal element of the second metal oxide layer and the metal element of the CdS layer is 1: 1. do it.

The formation of the CdS layer may be performed in the same manner as in the step (i) except that a raw material liquid containing the raw material of the second metal oxide layer is used.

Next, the solar cell of the present invention will be specifically described based on Examples, Example 1

A solar cell was fabricated in which the transparent electrode layer was composed of a first metal oxide layer having a high impurity concentration on the transparent substrate side and a second metal oxide layer having a low impurity concentration on the n-type compound semiconductor layer side.

(i) Formation of the first metal oxide layer

A layer of tin oxide containing fluorine as an impurity (about 0.4 / xm) was formed on a borosilicate glass substrate (600 mm x 271 mm x 3 mm).

Specifically, a raw material solution obtained by dissolving 100 g of dimethyltin dichloride powder and 4 g of ammonium fluoride powder in 360 cc of water was prepared at a frequency of 1 MHz. The ultrasonic vibrator was put into a container with a built-in ultrasonic vibrator, and the ultrasonic vibrator was operated to atomize the raw material liquid. Then, the fine particles of the atomized raw material liquid are jetted out of the fine particle jet port together with the air introduced from the carrier gas inlet pipe, introduced into the Matsufur furnace through the fine particle inlet pipe, and placed on the metal conveyor belt moving inside the furnace. It was brought into contact with the surface of the placed glass substrate.

The surface temperature of the glass substrate was kept at 560 ° C by heat transfer from the conveyor belt heated by the heater and radiant heat in the Matsufur furnace. Twenty-five seconds after the fine particles of the raw material liquid were introduced into the muffle furnace, a fluorine-containing tin oxide layer was formed on the glass substrate. Unused fine particles of the raw material liquid were discharged through a discharge pipe.

(ii) Formation of second metal oxide layer

After the formation of the first metal oxide layer, the glass substrate was once returned to normal temperature, and the raw material liquid in the container was replaced with the raw material liquid for the second metal oxide layer. As the raw material liquid for the second metal oxide layer, a raw material liquid in which 100 g of dimethyltin dichloride powder was dissolved in 360 cc of water was used. That is, the raw material liquid for the second metal oxide layer does not contain fluorine.

Fine particles of the raw material liquid were introduced into the Matsufuru furnace in the same manner as the first metal oxide layer, and the surface temperature of the first metal oxide layer was maintained at 560 ° C in the same manner as described above. Was introduced into the Matsufur furnace, and a tin oxide layer having a thickness of about 0.2 / m was formed on the first metal oxide layer in 10 seconds.

(ii) Formation of n-type compound semiconductor layer

On the second metal oxide layer, a sulfide sulfur layer was formed. Specifically, a raw material solution prepared by dissolving cadmium rubumic acid, a cadmium gentil, in toluene is placed in a container with a built-in ultrasonic vibrator at a frequency of 1 MHz, and the ultrasonic vibrator is operated to atomize the raw material liquid. I let it. The fine particles of the atomized raw material liquid are ejected from the fine particle ejection port together with the nitrogen introduced from the carrier gas introduction pipe. Then, it was introduced into a Matsufuru furnace through a fine particle introduction tube, and was brought into contact with the surface of a substrate having a tin oxide layer placed on a metal conveyor belt moving in the furnace. The surface temperature of the tin oxide layer was maintained at 450 ° C. in the same manner as described above. In 30 seconds after the fine particles of the raw material liquid were introduced into the muffle furnace, a sulfurating force layer with a thickness of about 0.08 m was formed on the tin oxide layer.

(iv) Formation of p-type compound semiconductor layer

Sulfurizing force A tellurium dominating layer was formed on the dominating layer. Specifically, a substrate having a cadmium sulfide layer is placed on a carbon support on which cadmium telluride powder is placed via a glass spacer having a thickness of 3 mm. The powder faced the cadmium sulfide layer. Then, under a nitrogen atmosphere of 1 Torr, the temperature of the substrate was kept at 550 ° C (: the temperature of the cadmium telluride powder on the support was kept at 750 ° C. After 4 minutes, the sulfuric acid layer was formed. A 5 m thick telluride layer was formed on top.

(V) Solar cell assembly

A carbon electrode was formed on the cadmium telluride layer. Next, silver electrodes were formed as collector electrodes on the exposed portions of the carbon electrode and the remaining transparent electrode layer, respectively, to assemble a sulphide-dominium / tellurium-dominium-dominium solar cell.

(vi) Analysis of transparent electrode layer

[Analysis of transparent electrode layer by XPS]

The transparent electrode layer composed of the first metal oxide layer and the second metal oxide layer was analyzed by XPS (X-ray photoelectron spectroscopy). The elemental compositions at the surface of the first metal oxide layer (first layer) and the second metal oxide layer (second layer) and at a depth of 100 angstroms are shown. Figure 1 shows. The values in Table 1 are in atomic%. table 1

Table 1 shows that the second oxide layer does not contain fluorine. The results show that the second oxide layer has high resistance.

[Simulation of Sulfidation Dummy Layer and Transparent Electrode Layer by SIMS]

The sulfur sulfide layer and the transparent electrode layer were analyzed by SIMS (secondary ion mass spectrometry). Figure 1 shows the relationship between the secondary ion intensity and the measurement cycle. The measurement cycle on the horizontal axis corresponds to the depth from the surface of the sample. In FIG. 1, the vicinity of the 30th cycle corresponds to the interface between the sulfuric acid layer and the tin oxide layer.

FIG. 1 shows that the second metal oxide layer and the cadmium sulfide layer contain fluorine diffused from the first metal oxide layer. It is probable that such low-concentration fluorine could not be detected because XPS could not detect elements with an abundance of less than about 0.1%. On the other hand, S IMS can detect elements at the level of p pm to p p b.

In FIG. 1, the secondary ion intensity (corresponding to the fluorine concentration) of fluorine at the center in the thickness direction of the second metal oxide layer is about 1200 counts, and the thickness direction of the first metal oxide layer is The secondary ion intensity of fluorine at the center of is about 2400 counts, and the intensity ratio is about 1: 2. Thus, the second metal oxide layer having a low fluorine concentration has a function of suppressing the diffusion of fluorine into the sulfur-doping layer and maintaining the strength of the sulfur-doping layer.

[Analysis of transparent electrode layer by scanning electron microscope] FIG. 2 shows a scanning electron micrograph of a cross section of the transparent electrode layer composed of the first metal oxide layer and the second metal oxide layer. In FIG. 2, the thickness of the first tin oxide layer of about 0.4 / zm and the thickness of the second tin oxide layer of about 0.2 / m are about 0.6 / xm. Can be observed.

(vii) Evaluation of solar cells

The open-circuit voltage, current density, fill factor, and conversion efficiency of the obtained solar cells were measured using a solar simulator. The size of the sub-module is 600 mm X 27 1 mm and has 180 cells (3 X 60). Fig. 3 shows the distribution of open circuit voltage, Fig. 4 shows the distribution of fill factor, Fig. 5 shows the distribution of current density, and Fig. 6 shows the distribution of conversion efficiency. The average open-circuit voltage in the plane is

0.720 V, the average fill factor was 0.593, the average current density was 25.7 mA, and the average conversion efficiency was 11.0%. Example 2

After the formation of the first metal oxide layer, the second metal oxide layer was formed continuously without returning the glass substrate to room temperature. That is, a container for the raw material liquid for the first oxide layer and a container for the raw material liquid for the second oxide layer are prepared, and a fine particle outlet and a fine particle introduction tube for introducing each raw material liquid into the Matsufur furnace are also provided. I prepared each. After the formation of the first oxide layer, the remaining fine particles of the raw material liquid were discharged from the Matsufur furnace, and the second metal oxide layer was continuously formed. The formation time of the second metal oxide layer was 25 seconds, and the formation time of the second metal oxide layer was 10 seconds. Otherwise, a solar cell was assembled in the same manner as in Example 1. The obtained solar cell was evaluated in the same manner as in Example 1. The average open-circuit voltage was 0.750 V, the average fill factor was 0.601, the average current density was 25.5 mA, and the average conversion efficiency was 11.5%.

The better result than the solar cell of Example 1 was obtained because of the shape of the transparent electrode layer. It is considered that a uniform transparent electrode layer was obtained because there was no temperature change during the formation. Example 3

In this example, impurities were removed from the vicinity of the surface of the metal oxide layer by forming a metal oxide layer containing impurities on a glass substrate as described below and then heating in a reducing atmosphere.

A tin oxide layer containing fluorine as an impurity was formed on a borosilicate glass substrate (600 mm × 271 mm × 3 mm) in the same manner as in the first metal oxide layer of Example 1. However, the formation time of the tin oxide layer was set to 30 seconds, and the thickness of the layer was set to about 0.6 / 2 m.

Next, the glass substrate having the tin oxide layer was placed on a metal conveyor belt moving in a Matsufur furnace. The nitrogen atmosphere (reducing atmosphere) in the Matsufuru furnace was controlled to an oxygen concentration of 30 ppm or less. The surface temperature of the glass substrate was maintained at 560 ° C for 5 minutes by the heat transfer from the conveyor belt heated by the heater and the radiant heat in the Matsufur furnace.

Thereafter, an n-type compound semiconductor layer, a p-type compound semiconductor layer and an electrode were formed on the transparent electrode layer after the heat treatment in the same manner as in Example 1, and a solar cell was assembled.

When the transparent electrode layer was analyzed by XPS, fluorine as an impurity was not detected in the transparent electrode layer near the n-type compound semiconductor layer.

Therefore, by heating the transparent electrode layer containing impurities in a reducing atmosphere, fluorine near the surface of the transparent electrode layer is removed, the impurity concentration is high on the transparent substrate side, and the n-type compound semiconductor layer side Thus, it can be seen that a transparent electrode layer having a low impurity concentration can be formed.

The same evaluation as in Example 1 was performed on the obtained solar cell. In plane The average open-circuit voltage was 0.745 V, the average fill factor was 0.610, the average current density was 25.6 mA, and the average conversion efficiency was 11.6%. Example 4

(i) Production of solar cell

A solar cell having a mixed crystal layer having a thickness of 10 Å or more consisting of the constituent elements of the transparent electrode layer and the n-type compound semiconductor layer between the transparent electrode layer and the n-type compound semiconductor layer was manufactured as follows. .

A transparent electrode layer composed of a first metal oxide layer and a second metal oxide layer is formed on a glass substrate in the same manner as in Example 1, and tin, oxygen, force, and sulfur are formed on the transparent electrode layer. A mixed crystal layer with a thickness of about 15 angstroms was formed.

Specifically, 100 g of dimethyltin dichloride and 100 g of cadmium rubamate, getylditi, are dissolved in toluene of l cc cc, and an ultrasonic vibrator with a frequency of 1 MHz is used. Was put into a container with a built-in, the ultrasonic vibrator was operated, and the raw material liquid was atomized. Fine particles of the atomized raw material liquid were ejected from the fine particle outlet together with air introduced from the carrier gas introduction pipe, and introduced into the muffle furnace through the fine particle introduction pipe. Fine particles introduced into the Matsufuru furnace were brought into contact with the surface of a substrate having a transparent electrode layer placed on a metal conveyor belt moving in the Matsufuru furnace to form a mixed crystal layer. The surface temperature of the substrate was kept at 420 ° C by the heat transfer from the conveyor belt heated by the heater and the radiant heat in the Matsufuru furnace. Ten seconds after the fine particles of the raw material liquid were introduced into the Matsufuru furnace, the inside of the Matsufuru furnace was evacuated.

Thereafter, an n-type compound semiconductor layer, a P-type compound semiconductor layer and an electrode were formed on the mixed crystal layer in the same manner as in Example 1, and a solar cell was assembled.

(ii) Analysis of mixed crystal layer [Analysis by Auger photoelectron spectroscopy]

A cadmium sulfide layer was formed on the mixed crystal layer in the same manner as in Example 1 except that the thickness was set to about 100 Å. Then, the obtained sample was analyzed by Auger photoelectron spectroscopy. Figure 7 shows the relationship between the obtained photoelectron intensity of each element and the depth from the surface of the sample. In FIG. 7, the zero point on the horizontal axis corresponds to the surface of the sulfur-doping layer.

At the interface between the tin oxide layer or the sulfur-doped layer and the mixed crystal layer, the photoelectric intensity of the element is considered to be the maximum intensity of 1 Z 2. In FIG. 7, the photoelectron intensity of sulfur and force dome is around 130 Å, and the photoelectron intensity of tin and oxygen is around 1100 Å, the maximum intensity being 1 Z 2. Therefore, it is considered that the portion having a thickness of about 10 to 20 angstroms when the depth from the sample surface is about 110 to 130 angstroms corresponds to the mixed crystal layer. Assuming that there is no mixed crystal layer, the points where the photoelectron intensity of each element is 1/2 should be aligned.

The results show that a mixed crystal layer consisting of tin, cadmium, sulfur, and oxygen and having a thickness of about 10 to 20 onda was formed at a depth of about 100 angstroms from the sample surface. I understand.

Next, the cadmium sulfide layer was removed from the same sample by spattering, and the mixed crystal layer was analyzed by Auger photoelectron spectroscopy. Figure 8 shows the relationship between the obtained photoelectron intensity and its energy.

Figure 8 shows peaks attributed to sulfur, cadmium, tin and oxygen. This analysis can detect information down to a depth of about 5 angstroms from the surface. Therefore, this result indicates that a mixed crystal layer having a thickness of at least 10 angstroms or more containing the above four elements is formed adjacent to the cadmium sulfide layer.

[Observation of mixed crystal layer by transmission electron microscope] Figure 9 shows a cross-sectional photograph of the mixed crystal layer that exists between the tin oxide layer and the sulfur layer. A mixed crystal layer having a thickness of about 10 angstroms can be observed at the arrow in FIG.

(iii) Evaluation of solar cells

The obtained solar cell was evaluated in the same manner as in Example 1. Fig. 10 shows the distribution of open-circuit voltage, Fig. 11 shows the distribution of fill factor, Fig. 12 shows the distribution of current density, and Fig. 13 shows the distribution of conversion efficiency. The average open-circuit voltage in the plane was 0.788 V, the average current density was 26.3 mA, the average fill factor was 0.648, and the average conversion efficiency was 13.5%. Example 5

In the present example, after forming the first metal oxide layer, simultaneously with the n-type compound semiconductor layer, a second metal oxide layer having a lower impurity concentration than the first metal oxide layer and a mixed crystal layer were formed. .

(i) Formation of first oxide layer

A tin oxide layer having a thickness of about 0.4 m similar to the first oxide layer of Example 1 was formed on a borosilicate glass substrate (600 mm × 271 mm × 3 mm).

(ii) Formation of second oxide layer, n-type compound semiconductor layer and mixed crystal layer

Under the atmosphere of the raw material of the second metal oxide layer, a sulfurating layer was formed on the tin oxide layer. Specifically, a raw material solution obtained by dissolving 100 g of dimethyltin dichloride powder in 360 cc of water is placed in a container with a built-in ultrasonic oscillator at a frequency of 1 MHz, and the ultrasonic oscillator is operated. The raw material liquid was atomized. And Fine particles of the atomized raw material liquid were ejected from the fine particle outlet together with nitrogen introduced from the carrier gas inlet pipe, and introduced into the Matsufuru furnace through the fine particle inlet pipe.

Next, a raw material solution obtained by dissolving cadmium getyl dithiocarbamate in toluene was introduced into the Matsufuru furnace through another fine particle ejection port and a fine particle introduction tube in the same manner as the dimethyltin dichloride raw material liquid. At this time, the fine particles introduced into the Matsufur furnace come into contact with the surface of the substrate having a tin oxide layer placed on a metal conveyor belt moving in the furnace, and are thermally decomposed to about 0.08 // m. A sulphide dome layer having a thickness of 3 mm was formed. Twenty seconds after the cadmium cadmium bamate solution was introduced into the Matsufur furnace, the Matsufur furnace was evacuated. The surface temperature of the substrate was maintained at 44 ° C by the heat transfer from the transport belt heated by the heater and the radiant heat in the Matsufur furnace. Thereafter, a P-type compound semiconductor layer and an electrode were formed in the same manner as in Example 1, and a solar cell was assembled.

(ii) Analysis of transparent electrode layer and mixed crystal layer

When the interface between the transparent electrode layer and the n-type compound semiconductor layer was analyzed by Auger photoelectron spectroscopy, a mixed layer consisting of sulfur, cadmium, tin and oxygen and having a thickness of about 10 angstroms was obtained. The presence of a crystalline layer was confirmed.

(iv) Solar cell evaluation

The obtained solar cell was evaluated in the same manner as in Example 1. The average in-plane open-circuit voltage was 0.802 V, the average fill factor was 0.60, the average current density was 26.5 mA, and the average conversion efficiency was 14.0. Comparative example A solar cell was fabricated and evaluated in the same manner as in Example 3, except that the heat treatment in the reducing atmosphere of the metal oxide layer was not performed. Figure 14 shows the distribution of open-circuit voltage, Figure 15 shows the distribution of fill factor, Figure 16 shows the distribution of current density, and Figure 17 shows the distribution of conversion efficiency. The average open-ended electrons in the plane were 0.592 V, the average current density was 24.9 mA, the average fill factor was 0.529, and the average conversion efficiency was 7.92%.

From the above, it can be seen that the solar cells of the examples are significantly improved in various performances as compared with the solar cells of the comparative examples. Further, it can be seen that the solar cells of the examples have little variation among cells. Industrial applicability

According to the present invention, a strong n-type compound semiconductor layer having high crystallinity can be formed on the transparent electrode layer. Therefore, the n-type compound semiconductor layer does not react with the p-type compound semiconductor layer and is not eroded. In addition, the electrical characteristics of the n-type compound semiconductor layer are improved. As a result, a solar cell having high current density and high conversion efficiency can be obtained.

Claims

The scope of the claims

1. A transparent substrate, a transparent electrode layer made of a metal oxide containing impurities formed on the transparent substrate, an n-type compound semiconductor layer formed on the transparent electrode layer, and formed on the n-type compound semiconductor layer A compound semiconductor solar cell comprising a p-type compound semiconductor layer,

A compound semiconductor solar cell, wherein an impurity concentration in the transparent electrode layer is high on the transparent substrate side and low on the n-type compound semiconductor layer side.

2. The compound semiconductor solar cell according to claim 1, wherein the transparent electrode layer is made of tin oxide containing a halogen element as an impurity.

3. The transparent electrode layer comprises a first metal oxide layer on the transparent substrate side and a second metal oxide layer on the n-type compound semiconductor layer side, and the impurity concentration in the first metal oxide layer is 2. The compound semiconductor solar cell according to claim 1, wherein the concentration is higher than an impurity concentration in the second metal oxide layer.

4. The ratio of the thickness of the second metal oxide layer to the thickness of the first metal oxide layer is 0.02 to 0.7, and the ratio of the second metal oxide layer to the impurity concentration in the first metal oxide layer is 4. The compound semiconductor solar cell according to claim 3, wherein the ratio of the impurity concentration in the two metal oxide layers is 0.5 or less.

5. A mixed crystal having a thickness of 10 angstroms or more between the transparent electrode layer and the n-type compound semiconductor layer and comprising a constituent element of the transparent electrode layer and the n-type compound semiconductor layer 2. The compound semiconductor solar cell according to claim 1, comprising a layer.

6. The transparent electrode layer is made of tin oxide containing a halogen element as an impurity, the n-type compound semiconductor layer is made of cadmium sulfide, and the mixed crystal layer is made of tin, cadmium, sulfur and oxygen. 6. The compound semiconductor solar cell according to item 5, wherein

7. The compound semiconductor solar cell according to claim 6, wherein the mixed crystal layer contains chlorine. ·

8. A step of forming a metal oxide layer containing impurities on a transparent substrate, a step of heating the metal oxide layer in a reducing atmosphere, and a step of subsequently forming an n-type compound semiconductor layer on the metal oxide layer. 2. The method for producing a compound semiconductor solar cell according to claim 1, comprising:

9. A step of forming a first metal oxide layer containing impurities on a transparent substrate, a second metal oxide containing impurities on the first metal oxide layer at a lower concentration than the first metal oxide layer. 4. The method for producing a compound semiconductor solar cell according to claim 3, comprising a step of forming a layer.

10. The compound semiconductor solar cell according to claim 9, wherein after the formation of the first metal oxide layer and before the formation of the second metal oxide layer, the temperature of the transparent substrate is temporarily lowered to room temperature. Manufacturing method.

11. The method for manufacturing a compound semiconductor solar cell according to claim 9, wherein after forming the first metal oxide layer, the second metal oxide layer is formed without lowering the temperature of the transparent substrate.

12. A step of forming a metal oxide layer containing impurities on a transparent substrate, and a step of forming an n-type compound semiconductor layer on the metal oxide layer in an atmosphere containing a raw material of the metal oxide. 6. The method for producing a compound semiconductor solar cell according to claim 5, comprising:

13. The method for manufacturing a compound semiconductor solar cell according to claim 12, wherein the atmosphere is obtained by vaporizing or atomizing a liquid comprising the metal oxide raw material and a solvent or a dispersion medium.

14. The method for producing a compound semiconductor solar cell according to claim 12, wherein the raw material of the metal oxide comprises a halide containing at least tin or zinc.

15. The method for producing a compound semiconductor solar cell according to claim 14, wherein said halide is dimethyltin dichloride or methyl zinc chloride.

16. A step of forming a metal oxide layer containing impurities on a transparent substrate, a step of applying a material of the metal oxide on the metal oxide layer, and thereafter, an n-type compound semiconductor on the metal oxide layer Claims having a step of forming a layer

6. The method for producing a compound semiconductor solar cell according to item 5.

17. The method for producing a compound semiconductor solar cell according to claim 16, wherein the raw material of the metal oxide comprises a halide containing at least tin or zinc.

18. A step of forming a metal oxide layer containing impurities on a transparent substrate, using a mixture of the metal oxide raw material and the n-type compound semiconductor raw material on the n-type compound semiconductor on the metal oxide layer The method for producing a compound semiconductor solar cell according to claim 5, further comprising a step of forming a layer.

19. The method for manufacturing a compound semiconductor solar cell according to claim 18, wherein the raw material of the metal oxide comprises a halide containing at least tin or zinc.