JP2975751B2 - Photovoltaic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic device such as a solar cell.

[0002]

2. Description of the Related Art Conventionally, in a photovoltaic device using a substrate of stainless steel or the like, a problem may occur in the element structure because the substrate has conductivity.

FIG. 4 is an element structure diagram of a conventional photovoltaic device using a thin film semiconductor as a photoelectric conversion layer. This photovoltaic device is generally referred to as a so-called integrated solar cell, and is characterized by forming a large number of solar cell portions (47) (47). These solar cells (47)
(47) ... is to obtain a high voltage by electrically connecting them in series.

[0004] In the figure, (41) is a non-translucent conductive substrate such as a stainless steel or metal substrate, and (42) is an insulating layer made of silicon oxide or silicon nitride formed on the surface of the non-translucent conductive substrate (41). The membrane, (43) (43) ... is the first made of chromium or aluminum
The electrodes, (44) (44) ... are photoelectric conversion layers made of amorphous silicon or the like, and (45) (45) ... are tin oxides which function as electrodes for taking out photogenerated carriers while securing the incidence of external light. , Indium tin oxide, etc., (46), (46) are used as auxiliary to efficiently extract photo-generated carriers reaching the transparent conductive films (45), (45). Collector electrode made of silver, nickel, aluminum, etc.

[0005] This photovoltaic device has a non-translucent conductive substrate (4).
1) A plurality of solar cell portions (47) formed on the first electrode (43), the photoelectric conversion layer (44), and the transparent conductive film (45) are provided along the surface thereof. With each solar cell unit (4
7) (47) are connected to adjacent solar cell units (47) (47) so as to be connected in series.

In such a photovoltaic device, the solar cell unit (4
7) Since it is necessary to first form (47)... Electrically insulated, the first electrode (43) and the non-translucent conductive substrate (4) are formed.
An insulating film (42) is interposed between the insulating film (1).

That is, if the solar cell portions (47) (47) are formed without the interposition of the insulating film (42), the solar cell portion (47) is formed by the conductivity of the non-translucent conductive substrate (41). ) (47)... Are electrically short-circuited.

In general, in a photovoltaic device, incident light cannot be completely absorbed by a single passage through the photoelectric conversion layers (44) (44). In order to be hardly absorbed, it is necessary to travel in the photoelectric conversion layer over a long distance.

Therefore, it is important to positively utilize the light reaching the first electrodes (43) and (43) to increase the conversion efficiency.

Regarding such an element structure, for example,
It is described in detail in 8-115872.

[0011]

However, an insulating film (42) newly formed on the surface of the non-translucent conductive substrate (41) as in the conventional photovoltaic device generally has a metal film (43) serving as an electrode. ) And the thin film semiconductor used as the photoelectric conversion layer (44) are formed by a method different from that of the thin film semiconductor, so that the manufacturing process of the photovoltaic device is complicated and the yield is reduced.

Furthermore, even if an attempt is made to use light that could not be absorbed by passing through the photoelectric conversion layers (44) (44) once,
In the conventional photovoltaic device, since the first electrodes (43) (43) are made of metal or the like, their surfaces are usually flat, and light is simply reflected without being scattered. For this reason, sufficient light could not be used yet.

[0013]

The feature of the photovoltaic device of the present invention resides in that an insulating metal oxide film and the same metal as the metal oxide film are formed on a non-translucent conductive substrate. The conductive metal oxide film, the photoelectric conversion layer, and the transparent electrode are formed in this order, and the conductive metal oxide film is used as an electrode. And that the conductive metal oxide film contains crystal grains, and furthermore, the metal oxide film is made of tin oxide, zinc oxide, indium oxide, or indium tin oxide. 5 withstand voltage of metal oxide film
0 kV / cm or more.

[0014]

According to the photovoltaic device of the present invention, a conductive metal oxide film mainly composed of the same metal as the insulating metal oxide film is interposed between the insulating metal oxide film and the photoelectric conversion layer. This is an electrode.

This is achieved by controlling the mixing ratio of the metal and oxygen, which are the main components of the insulating metal oxide film, the bonding ratio, or the addition of a new additive. Since the oxide film can be a conductive film, the metal oxide film having the conductivity is used as an electrode of the photovoltaic device, and as a result, the manufacture of the photovoltaic device itself can be simplified.

Further, since these metal oxide films contain crystal grains, the surface of the formed film is provided with an uneven shape. In particular, since the base of the conductive metal oxide film functioning as the first electrode is an insulating metal oxide film containing crystal grains, the crystal grains of the conductive metal oxide film are
Large crystal grains are further affected by the underlayer.

As a result, the surface of the conductive metal oxide film can be provided with a sufficient uneven shape suitable for scattering light.

[0018]

FIG. 1 shows a first embodiment of a photovoltaic device according to the present invention, and is a structural view of a so-called integrated solar cell. In the figure
(1) is a non-translucent conductive substrate such as stainless steel or aluminum, and (2) is an insulating metal oxide film (film) having crystal grains of tin oxide or indium oxide, or zinc oxide or indium tin oxide. Thickness about 1.5μm, Dielectric strength 70
kV / cm), (3) functions as a first electrode, and is a conductive metal oxide film having crystal grains containing the same metal as the main component as the insulating metal oxide film (2). (Approximately 200 Ω / □), and (4) a photoelectric conversion layer, which is formed by a pin junction using amorphous silicon (a-Si) as a base material in this example. (5) is a transparent conductive film made of an oxide indium or the like serving as a light incident side electrode, (6) is a collector electrode made of an aluminum film or the like, and (7) is a pair of a first electrode (3) and a photoelectric electrode. This is a solar cell section including a conversion layer (4) and a transparent conductive film (5).
In particular, in this device, the solar cell units (7) (7)
They are formed along the surface of (1), and they are electrically connected in series.

As a specific forming procedure, an insulating tin oxide is formed as an insulating metal oxide film (2) on a stainless non-translucent conductive substrate (1), and then a conductive metal oxide film is formed. Membrane (3)
To form conductive tin oxide. Then, only the conductive metal oxide film (3) is patterned with a solution of ferric dioxide in order to separate each of the solar cells (7) (7)... Then, after the amorphous silicon to be the photoelectric conversion layer (4) is formed, the photoelectric conversion layer (4) is patterned to separate each of the solar cell sections (7) (7). Then, a transparent conductive film (5) on the light incident side is formed and then patterned, and finally, a collector (6) is formed and then patterned to complete the element.

In particular, in the embodiment, the insulating metal oxide film (2)
As the conductive metal oxide film (3), tin oxide which can be formed by a sputtering method was used. Therefore, an insulating metal oxide film is used as a sputtering target (evaporation source).
The insulating metal oxide film (2) and the conductive metal oxide film (3) can be obtained by installing the one for (2) and the one for conductive metal oxide film (3) in the sputter deposition apparatus, respectively. Can be sequentially formed, and the metal oxide films (2) and (3) can be continuously formed without exposing the interface between them.

Table 1 shows typical conditions for forming these metal oxide films (2) and (3). The table also shows the conditions for forming the transparent conductive film (5) by the sputtering method.

[0022]

[Table 1]

In the present embodiment, the conductive metal oxide film (3) is formed in order to make the metal oxide film conductive.
Tin oxide (SnO ₂ ) doped with 1% of Sb is used as a target.

The components other than the insulating metal oxide film (2) and the conductive metal oxide film (3) are conventionally known.

In the photovoltaic device of the present invention, since the metal oxide film capable of increasing the crystal grains relatively easily is used as the first electrode, the uneven shape based on the crystal grains is formed on the surface of the metal oxide film. Can be provided. In particular, the conductive metal oxide film with the crystal grains of the insulating metal oxide film (2) as nuclei
Since (3) is grown, the size of the crystal grains of the conductive metal oxide film (3) can be further increased.

This means that the thickness of the conventional photovoltaic device differs from that of the conventional photovoltaic device in which only a conductive metal oxide film, for example, only indium tin oxide is used. In other words, if only the conductive metal oxide film is used, if a sufficient unevenness is to be provided, the thickness of the conductive metal oxide film will be greatly increased, resulting in inconvenience in the formation surface.

However, in the photovoltaic device of the present invention, the growth mechanism affected by the underlayer is used, so that the surface of the first electrode (3) can be formed without unevenness without increasing the film thickness too much. The size of the crystal grains can be increased. Incidentally, it is sufficient that the thickness of the insulating metal oxide film (2) is about 1 μm.

Table 2 shows typical conditions for forming amorphous silicon used as the photoelectric conversion layer (4).

[0029]

[Table 2]

Incidentally, as the patterning of the metal oxide film,
The patterning method is not limited to the wet etching as in this example, but may be a patterning method by a dry process using plasma or ions.

In particular, the tin oxide used as the metal oxide films (2) and (3) has a higher absorption coefficient for near-infrared light when the conductive tin oxide (3) is used than the insulating tin oxide (2). Since it has a characteristic that is greater than one digit, by selecting the wavelength of the laser light, only the conductive tin oxide (3) can be selectively patterned by the laser light. Therefore, when tin oxide is used as the metal oxide film, the laser patterning method can be used, and the process can be further simplified.

Table 3 is a characteristic table of the photovoltaic device according to the embodiment of the present invention. The table also shows a conventional photovoltaic device (integrated solar cell). This conventional photovoltaic device has a structure in which a conventional silicon oxide film (SiO ₂ ) is applied instead of the insulating metal oxide film (2) in the structure of the photovoltaic device of the present invention. The first electrode is made of silver.

[0033]

[Table 3]

The examples in the table are all photovoltaic devices of 10 cm square, and the light irradiation conditions are AM-1.5, 100 mW / c.
m ² .

According to the photovoltaic device of the present invention, the short-circuit current is increased from 118.8 mA to 121.6 mA as compared with the conventional device, and the conversion factor is also improved as a whole by improving the fill factor. Has been achieved.

In particular, the short-circuit current can be improved by using a material having crystal grains as the first electrode (3), so that the surface thereof can be provided with an uneven shape suitable for scattering of light. This is because effective use could be achieved.

Next, the dielectric strength required for the insulating metal oxide film (2) used in the present invention will be described. This is because the metal oxide film used in the present invention is generally used as a conductive film, and therefore, the insulating property when used as the insulating metal oxide film (2) in the photovoltaic device of the present invention. Is a problem.

FIG. 2 is a characteristic diagram showing the relationship between the dielectric strength of the insulating metal oxide film (tin oxide) and the yield of the photovoltaic device. The dielectric breakdown voltage was changed by changing the mixture ratio of the metal and oxygen used, and 100 samples of a so-called integrated solar cell were used for the evaluation.
The thickness of the metal oxide film is constant at 1.2 μm.

According to this result, there was no large change in the output characteristics of the photovoltaic device, but the dielectric strength was 50 kV /
In a region less than 1 cm, a significant decrease in yield is observed.
It was found that a dielectric breakdown voltage of 50 kV / cm or more was required. On the other hand, if the conductivity of the conductive metal oxide film (3) is not more than 500Ω / □ in sheet resistance, there is no practical problem.

FIG. 3 is a diagram showing an element structure of a photovoltaic device according to a second embodiment of the present invention, which comprises only one solar cell unit. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals.

By using an insulating metal oxide film (2) and a conductive metal oxide film (3) as in the first embodiment, it is possible to provide a good concavo-convex shape.

The materials used in this embodiment are formed under the same conditions as those used in the first embodiment.

Next, the electrical characteristics of the photovoltaic device of the present invention will be described. Table 4 shows that light irradiation (AM-
1.5, 100 mW / cm ² ). In the same table, for comparison, in the structure of the photovoltaic device of the present invention, a conventional silicon oxide film (SiO ₂ ) was applied instead of the insulating metal oxide film (2). The electrode using silver as the first electrode (3) is shown as a conventional example.

[0044]

[Table 4]

According to the photovoltaic device of the present invention, the short-circuit current is 16.78 mA / cm ² to 1
The conversion efficiency has been improved as a whole by increasing to 7.05 mA / cm ² and further improving the fill factor.

As a method for controlling the sheet resistance of the tin oxide used in the embodiment, a halogen element such as fluorine (F) or Sb or the like may be added in an amount of 5 × 10 ¹⁹ cm ⁻³ or more. In addition, in the case of zinc oxide (ZnO) which can be used as the metal oxide film of the present invention, as a method of controlling the sheet resistance, a Group III element such as aluminum (Al) is used in an amount of 5 × 10 ¹⁹ cm. ^It can be used by adding ^-3 or more.

Further, in the embodiment, as the method of forming the metal oxide film, the insulating and conductive films were formed by the same forming apparatus. However, in order to avoid mutual diffusion of impurities, separate vacuum chambers were used. It may be formed.

As another method for forming tin oxide, S
A gas such as n (CH ₃ ) ₄ , SnCl ₄ , O ₂ , CF ₄ , F ₂ or the like may be used in combination to form a gas by a thermal CVD method, a MOCVD method, or the like.

For zinc oxide, Zn (C ₂ H ₅ ) ₂ , O ₂ , H
Thermal CVD or MOCVD by combining gases such as ₂ O
It may be formed by a forming method such as a method, or may be formed by an electron beam evaporation method.

Further, as a method of forming a conductive metal oxide film which is a feature of the photovoltaic device of the present invention, in addition to the formation by film formation as in the embodiment, an insulating metal oxide film formed beforehand may be used. The effect of the present invention can be similarly obtained even when only the surface of the metal oxide film is made conductive by ion implantation or plasma doping.

In addition, indium oxide or indium tin oxide can be used as the metal oxide film of the present invention.

Since the metal oxide film used in the photovoltaic device of the present invention has a relatively high translucency, light not absorbed in the photoelectric conversion layer (5) is used as the first electrode. Considering the light loss caused by further passing through the functional conductive metal oxide film, a highly light-reflective metal film, for example, silver, is provided between the insulating metal oxide film (2) and the non-translucent conductive substrate (1). Interposing a thin film is effective in improving the characteristics.

Incidentally, since the high-reflection metal film such as silver can be formed by a sputtering method or the like, it can be formed continuously with insulating and conductive metal oxide films. As specific forming conditions, silver is used as a sputtering target, the substrate temperature is 400 ° C., the high-frequency power is 500 W, and the degree of vacuum during sputtering is 0.
004 Torr, argon (gas flow rate 20 sccm) may be used as a sputtering gas. A typical film thickness is about 3000 °.

[0054]

According to the photovoltaic device of the present invention, a conductive metal oxide film mainly composed of the same metal as the insulating metal oxide film used for insulating the non-translucent conductive substrate is used as an electrode. Therefore, these metal oxide films can be formed continuously, so that the process can be simplified and the yield can be improved.

Further, by forming a conductive metal oxide film on an insulating metal oxide film containing crystal grains, the conductive metal oxide film is affected by the base, and large crystal grains can be formed. This means that if this conductive metal oxide film is used as an electrode, light can be efficiently scattered, and the conversion efficiency as a photovoltaic device can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view of the element structure of a first embodiment of the photovoltaic device of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the dielectric strength of an insulating metal oxide film used in the present invention and the yield of a photovoltaic device.

FIG. 3 is a sectional view of an element structure according to a second embodiment of the photovoltaic device of the present invention.

FIG. 4 is a sectional view of an element structure of a conventional photovoltaic device.

[Explanation of symbols]

(1) ... non-translucent conductive substrate (2) ... insulating metal oxide film (3) ... conductive metal oxide film (4) ... photoelectric conversion layer (5) ... transparent conductive film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-17287 (JP, A) JP-A-59-55080 (JP, A) JP-A-58-115572 (JP, A) 62974 (JP, a) JP Akira 59-184574 (JP, a) JitsuHiraku flat 3-97946 (JP, U) (58 ) investigated the field (Int.Cl. ^6, DB name) H01L 31/04 - 31 / 078

Claims (4)

(57) [Claims] An insulating metal oxide film, a conductive metal oxide film containing the same metal as the main component and having a conductive property, a photoelectric conversion layer, and a transparent electrode on a non-translucent conductive substrate. Are formed in this order, and the conductive metal oxide film is used as an electrode. 2. An insulating metal oxide film containing crystal grains on a non-translucent conductive substrate, and a conductive metal oxide film containing the same metal as the main component and containing crystal grains. A photovoltaic device, wherein a photoelectric conversion layer and a transparent electrode are formed in this order, and the conductive metal oxide film is used as an electrode. 3. The photovoltaic device according to claim 1, wherein the metal oxide film is made of tin oxide, zinc oxide, indium oxide, or indium tin oxide. 4. The photovoltaic device according to claim 1, wherein the insulating metal oxide film has a withstand voltage of 50 kV / cm or more.