JP2001196615A - Integrated thin film solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify integration using laser scribing without generating deterioration in transducer efficiency per effective area in an integrated thin film solar battery. SOLUTION: A transparent electrode layer 12, a crystalline silicon system photoelectric transducer unit layer 14, and a back face electrode layer 16 laminated on a transparent insulating substrate 11 are separated by plural separating grooves 13 and 17 so that plural photoelectric transducer cells can be formed, and the plural cells are electrically and serially connected through the plural connecting grooves 15 in this integrated thin film solar battery. The transparent electrode layer includes a primary thickness part 12 including at least either tin oxide or ITO as primary components and a zinc oxide coating layer 12a whose thickness ranges from 50 to 500 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated thin-film solar cell, and more particularly to a technique for easily realizing good and stable photoelectric conversion characteristics in an integrated thin-film solar cell manufactured by using laser scribe. is there.

In the specification of the present application, the terms “polycrystalline”, “microcrystalline” and “crystalline” refer to a partially amorphous state as generally used in the technical field of thin-film solar cells. Is also meant.

[0003]

2. Description of the Related Art A solar cell which is a typical example of a semiconductor photoelectric conversion device includes a single crystal solar cell using a single crystal semiconductor wafer and a thin film solar cell using a semiconductor thin film. The thin-film solar cell has an advantage that the area can be easily increased and can be manufactured at low cost as compared with the single-crystal solar cell.

FIG. 2 is a schematic sectional view showing a typical example of a thin-film solar cell. In each drawing of the present application, the dimensional relationship such as the thickness of the illustrated layer is appropriately changed for clarification and simplification of the drawing, and does not reflect the actual dimensional relationship.

In a thin-film solar cell as shown in FIG. 2, a first electrode layer 2, a p-type or n-type one conductivity type layer 3, a substantially i-type photoelectric layer are formed on an insulating substrate 1. Conversion layer 4,
An n-type or p-type reverse conductivity type layer 5 and a second electrode layer 6 are sequentially stacked. That is, in general, in a thin-film solar cell, the photoelectric conversion unit 10 includes the p-type layer 3 or 5.
And an n-type layer 4 sandwiched between the n-type layer 5 and 3. The i-type layer 4 having a relatively large thickness mainly causes a photoelectric conversion effect, and the p-type layer 3 which is much thinner than the i-type layer 4
Alternatively, 5 and n-type layer 5 or 3 act to generate an electric field. Regarding the thin-film photoelectric conversion unit 10 including the p-type layer, the i-type layer, and the n-type layer, the i-type layer 4 as the photoelectric conversion layer is formed regardless of whether the p-type layer and the n-type layer are crystalline or amorphous. A crystalline unit is referred to as a crystalline unit, and an i-type layer having an amorphous layer is referred to as an amorphous unit.

Here, the crystalline i-type layer can absorb light having a longer wavelength than the amorphous i-type layer, and the crystalline thin-film photoelectric conversion unit has a longer wavelength than the amorphous thin-film photoelectric unit. Has the advantage that this light can also be used for photoelectric conversion.

However, the thickness of the amorphous i-type photoelectric conversion layer included in the amorphous thin-film photoelectric conversion unit is generally about 0.3 μm.
m or less is sufficient, but considering the light absorption coefficient of crystalline silicon, the crystalline i-type photoelectric conversion layer included in the crystalline thin film photoelectric conversion unit generally needs to have a thickness of about 2 μm or more. You. That is, the thickness of the crystalline i-type photoelectric conversion layer included in the crystalline thin-film photoelectric conversion unit is required to be about several times or more the thickness of the amorphous i-type photoelectric conversion layer included in the amorphous thin-film photoelectric conversion unit. You.

Therefore, Japanese Patent Application Laid-Open No. 11-145499 discloses a method of depositing a crystalline i-type photoelectric conversion layer by plasma CVD under a pressure of 133 Pa (1 Torr) or less under a high pressure of 400 Pa (3 Torr) or more. It discloses that a high-quality crystalline i-type photoelectric conversion layer can be deposited at a high speed by performing the process with the flow ratio of hydrogen gas to system gas increased to 50 times or more.

In the manufacture of thin-film solar cells, a desired structure is generally formed by a manufacturing process including an appropriate repetition or combination of a deposition step of a thin film by a CVD method or sputtering and a patterning step by a laser scribe method or the like. Is done. That is, usually, an integrated structure in which a plurality of photoelectric conversion cells are electrically connected in series on one insulating substrate is employed. In a power solar cell for outdoor use, for example, 0.4 m × 0.8 m Is used, and a device capable of generating a high output voltage is used.

FIG. 3 is a schematic cross-sectional view showing the structure of a typical example of a conventional integrated thin-film solar cell. In this integrated thin-film solar cell, a transparent electrode layer 12 and a semiconductor photoelectric conversion layer 1 made of silicon or the like are formed on a transparent insulating substrate 11.
4 and the back electrode layer 16 are sequentially laminated, and photoelectric conversion cells adjacent to each other on the left and right sides are electrically connected in series via a connection opening groove 15 provided in the semiconductor layer 14 by laser scribing. . As the transparent electrode layer 12, a film of a transparent conductive oxide (TCO) such as tin oxide, ITO (indium tin oxide) or the like, or a laminate thereof can be generally used. Further, as the back electrode layer 16, A
Metal films such as g, Al, and Cr can be used. The back electrode layer 16 may be formed as a laminate of a TCO film and a metal film.

An integrated thin-film solar cell having a structure as shown in FIG. 3 is generally manufactured by the following method. First, a TCO film is deposited as a transparent electrode layer 12 on a glass substrate 11, and the transparent electrode layer 12 is separated by a laser scribe method in order to separate the transparent electrode layer 12 into a plurality of regions corresponding to a plurality of strip-shaped photoelectric conversion cells. Separation groove 1
3 is formed. At this time, the focal point of the laser beam is adjusted so as to be suitable for blowing off the transparent electrode layer 12 locally. The transparent electrode separation groove 13 thus formed extends linearly in a direction perpendicular to the plane of FIG.

Then, a pin is formed by plasma CVD so as to cover the transparent electrode layer 12 separated into a plurality of regions.
A silicon-based semiconductor photoelectric conversion unit layer 14 including a junction is deposited. The semiconductor layer 14 has a connection opening groove 1 for electrically connecting the left and right adjacent photoelectric conversion cells in series.
5 is formed by a laser scribe method. At this time, the focus of the laser beam is adjusted so as to be suitable for blowing off the semiconductor layer 14 locally. The connection groove 15 thus formed also extends linearly in a direction perpendicular to the paper surface of FIG.

Subsequently, a single layer or a multiple layer of a metal film of Ag, Al, Cr or the like is deposited as the back electrode layer 16 so as to fill the connection grooves 15 and cover the semiconductor layer 14. Similarly to the case of the transparent electrode layer 12, the back electrode separation groove 17 is formed by a laser scribe method so as to separate the back electrode layer 16 into a plurality of regions corresponding to a plurality of photoelectric conversion cells. At this time, the metal electrode layer 16 having a high reflectance
It is difficult to directly absorb laser light energy
The semiconductor layer 14 absorbs the laser light energy, and the metal layer 16 is blown off together with the semiconductor layer 14 locally. The back surface electrode separation groove 17 thus formed also extends linearly in a direction orthogonal to the paper surface of FIG.
It has a depth that reaches the electrode layer 12. In this way,
An integrated thin-film solar cell as shown in FIG. 3 is formed.

In such an integrated thin-film solar cell, the transparent electrode separating groove 13 for separating the transparent electrode layer 12 on the transparent substrate 11 is filled with a semiconductor layer 14 deposited on the transparent electrode layer 12. The semiconductor layer 14
Unnecessary contact is made in the direction parallel to the substrate 11 via the. In addition, the conductor formed in the connection groove 15 for connecting a plurality of cells is formed of p in the photoelectric conversion unit layer 14.
It is in contact with the side surfaces of all the semiconductor layers of the type, i-type and n-type. However, the thickness of the photoelectric conversion unit layer 14 in the thin-film solar cell is extremely thin, and particularly in the case of an amorphous silicon-based photoelectric conversion unit layer, the resistance of the amorphous silicon layer itself is high. And almost no current flows through the photoelectric conversion unit layer in the thickness direction of the photoelectric conversion unit layer. Therefore, the unnecessary contact as described above hardly adversely affects the performance of the photoelectric conversion unit.

That is, in the integrated type thin-film solar cell as shown in FIG.
And the back electrode 16 are in the area A, and the area B
Does little to generate electricity.

[0016]

As described above, in the integrated type thin film solar cell formed by using the laser scribe, the intensity and focus of the laser beam when forming the connection groove 15 and the back electrode separation groove 17 are described. There is the fact that the photoelectric conversion efficiency per effective area changes depending on the variation of the adjustment. That is, in order to obtain the best conversion efficiency per effective area in the integrated thin film solar cell, the allowable range of the laser beam irradiation condition is extremely limited, and it is not easy to accurately maintain the limited condition. .

In view of such circumstances, an object of the present invention is to easily realize good and stable photoelectric conversion characteristics in an integrated thin-film solar cell manufactured by using laser scribe.

[0018]

According to the present invention, a strip-shaped photoelectric conversion cell comprising a plurality of transparent electrode layers, at least one semiconductor photoelectric conversion unit layer, and a back electrode layer sequentially laminated on a transparent insulating substrate is provided. Are separated by a plurality of separation grooves that are substantially linear and parallel to each other to form
And in the integrated thin-film solar cell in which the plurality of cells are electrically connected to each other in series through the plurality of connection grooves parallel to the separation grooves, the transparent electrode layer is made of tin oxide and indium tin oxide. It is characterized by including a main thickness portion containing at least one as a main component and a zinc oxide coating layer having a thickness in the range of 50 to 500 nm.

Such a zinc oxide coating layer can act to protect the transparent electrode layer at the time of laser scribing used for integration of a thin-film solar cell, and furthermore, the crystalline semiconductor photoelectric conversion unit layer Can act to promote its crystal growth as it is deposited.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a more specific example of an embodiment of the present invention, an embodiment of the present invention will be described below together with a comparative example with reference to FIG.

(Embodiment 1) As an embodiment of the present invention, FIG.
An integrated crystalline thin-film solar cell having a configuration as schematically shown in FIG. First, 400mm x 30
White glass substrate 1 having an area of 0 mm and a thickness of 4 mm
1 on which a transparent electrode layer having a thickness of about 6
00 nm tin oxide film 12 and a thickness of about 20
A 0 nm zinc oxide coating film 12a was formed. By irradiating the transparent electrode layers 12 and 12a with a laser scribing YAG laser beam from the glass substrate 11 side, transparent electrode separation grooves 13 were formed at intervals of about 10 mm.

Next, the substrate 11 is transferred into a plasma CVD film forming chamber, and a p-type microcrystalline silicon layer having a thickness of 6 nm, a non-doped polycrystalline silicon layer having a thickness of 2.3 μm, and an n layer having a thickness of about 10 nm are formed. The crystalline semiconductor photoelectric conversion unit layer 14 was formed by depositing the type microcrystalline silicon layer. The film forming temperature at this time by plasma CVD was 250 ° C. This semiconductor layer 14 was also laser scribed using a YAG laser similarly to the case of the transparent electrode layers 12 and 12a, thereby forming the connection groove 15.

Thereafter, as the back electrode layer 16, a thickness of 90
A zinc oxide film having a thickness of 300 nm, an Ag film having a thickness of 300 nm, and a Ti film having a thickness of about 6 nm were deposited by sputtering.
The back electrode layer 16 thus formed was laser scribed similarly to the case of the semiconductor layer 14, thereby forming the back electrode separation groove 17. Note that this thin zinc oxide film is desirable in order to maintain a high light reflectance on the surface of the Ag film and to prevent Ag atoms from diffusing into the semiconductor layer 14, while a Ti film is a film in which the Ag film is in the air. This is desirable in order to prevent corrosion due to sulfur components and the like.

As described above, ten integrated solar cells in which 28 steps of strip-shaped cells were connected in series in the light receiving surface were manufactured. Of the five solar cells included in the group A1, the position of the target film for forming the groove is shifted by 3 mm from the focal position where the cross section of the laser beam is minimized toward the beam source, and the five solar cells included in the other group B1 The laser scribes were performed with a shift of 4 mm for one solar cell.

Photoelectric conversion characteristics when a total of 10 integrated thin-film solar cells of groups A1 and B1 were irradiated with AM1.5 light at 25 ° C. and 1 kW / m ² energy density using a solar simulator. There is no clear difference between the groups A1 and B1, and the average photoelectric conversion characteristics are that the open-circuit voltage is 13.8 V and the short-circuit current is 0.815
A, the fill factor was 0.714, and the effective conversion efficiency per effective area was 7.55%.

Comparative Example A solar cell of group A2 corresponding to group A1 in the same manner as in the example except that the thickness of the zinc oxide coating film 12a contained in the transparent electrode layer was reduced to 10 nm. Five solar cells and five solar cells of group B2 corresponding to group B1 were produced as comparative examples. The average photoelectric conversion characteristics when a total of 10 integrated thin-film solar cells of groups A2 and B2 were irradiated with light under the same conditions as in the example were as follows: open-end voltage: 13.5 V, short-circuit current: 0 .802A, the fill factor was 0.685, and the effective conversion efficiency per effective area was 6.97%.

In comparison between the above embodiment and the comparative example,
It can be seen that the ten solar cells according to the examples have better photoelectric conversion characteristics than the ten solar cells according to the comparative example. Further, between the groups A2 and B2 in the comparative example, the photovoltaic conversion characteristics of the solar cell of the group A2 in which the target film of the laser scribe is set closer to the beam focus tend to be lower than that of the group B2. there were.

The reason why the integrated thin-film solar cell according to the embodiment can exhibit excellent photoelectric conversion characteristics as compared with that of the comparative example can be considered as follows.

It is desired that a transparent conductive oxide (TCO) used as a transparent electrode material in a thin-film solar cell has high transparency and high conductivity. However, TC
In O, the higher the degree of oxidation, the higher the transparency, but the conductivity tends to decrease. Under the same transparency, tin oxide and ITO have better conductivity than zinc oxide. Therefore, conventionally, a zinc oxide layer is not used alone as a transparent electrode layer,
A tin oxide layer or an ITO layer is used alone.

However, tin oxide and ITO are chemically and thermally unstable as compared with zinc oxide. For example, when a semiconductor layer is deposited on a transparent electrode layer of tin oxide by a plasma CVD method, hydrogen plasma is used. The tin oxide transparent electrode layer may be damaged by a reducing action or the like. Therefore, conventionally, if desired, the surface of a transparent electrode layer of tin oxide or ITO is protected with a stable zinc oxide film. However, in this case, it is sufficient to protect only the surface of the transparent electrode layer of tin oxide or ITO from the plasma, and thus the thickness of the zinc oxide protective film is at most 5 nm to 10 nm. That is, the solar cell of the comparative example described above corresponds to a conventional example having a zinc oxide protective film having a maximum thickness.

However, when the semiconductor layer dividing groove and the back surface electrode separating groove are formed by laser scribing, the laser beam is irradiated through the transparent electrode layer. Therefore, in order to protect the transparent electrode layer from thermal degradation during laser scribing, it is considered that it is not sufficient to protect only the surface thereof. Then, if the tin oxide layer is thermally degraded, it is considered that the photoelectric conversion characteristics of the solar cell are deteriorated due to an increase in the resistivity. Furthermore, if the surface protective layer is insufficient,
It is considered that tin oxide partially sublimated from the surface adheres to the side wall in the back electrode separation groove, and a leak current is generated between the transparent electrode and the back electrode.

Under such circumstances, by forming a transparent electrode layer including a zinc oxide film having a large thickness range which has not been considered conventionally as in the present invention, the transparent electrode layer is formed during laser scribing. It is considered that thermal degradation and partial sublimation of the layer could be effectively suppressed.

Further, it is considered that the present invention has a particularly remarkable effect in a crystalline thin film solar cell. this is,
The crystalline silicon layer has a lower laser beam absorption efficiency than the amorphous silicon layer, and the crystalline photoelectric conversion layer has a larger thickness than the amorphous photoelectric conversion layer as described above. This is because a laser beam having a large energy density is required to form the division groove and the back electrode separation groove, and the possibility of causing thermal damage to the transparent electrode layer usually increases.

In the present invention, since the zinc oxide coating layer is deposited much thicker than before, the crystallization proceeds sufficiently, and this also promotes the crystallization of the crystalline photoelectric conversion unit layer deposited thereon. However, it is considered that the high-quality crystalline photoelectric conversion unit layer also acts to improve the conversion efficiency.

[0035]

As described above, according to the present invention, it is possible to provide a thin-film solar cell which can be easily integrated without lowering the conversion efficiency per effective area. Further, if a zinc oxide coating layer as in the present invention is used, even if the intensity of the laser beam used for forming the semiconductor layer dividing groove or the back electrode separating groove is somewhat too strong or the focal depth fluctuates. The conversion efficiency can be prevented from lowering. That is, according to the present invention, the tolerance of the intensity range and the focal depth range of the scribe laser beam is increased.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an integrated structure of an integrated thin-film solar cell according to one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing a basic laminated structure of a thin-film solar cell.

FIG. 3 is a schematic cross-sectional view showing an integrated structure of a conventional integrated thin-film solar cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Insulating substrate, 2 1st electrode layer, 3 1 conductivity type layer, 4
Substantially intrinsic photoelectric conversion layer, 5 reverse conductivity type layer, 6 back electrode layer, 10 thin film photoelectric conversion unit layer, 11 transparent insulating substrate, 12 transparent electrode layer, 12a zinc oxide coating layer, 1
3 transparent electrode separation groove, 14 thin film photoelectric conversion unit layer,
15 Opening groove for connection, 16 Back electrode layer, 17 Back electrode separation groove, A effective power generation area, B Non-power generation area.

Claims (2)

[Claims] 1. A transparent electrode layer, at least one semiconductor photoelectric conversion unit layer, and a back electrode layer, which are sequentially laminated on a transparent insulating substrate, are substantially linear so as to form a plurality of rectangular photoelectric conversion cells. An integrated thin-film solar cell which is separated by a plurality of separation grooves parallel to each other, and the plurality of cells are electrically connected to each other in series via a plurality of connection grooves parallel to the separation groove. The transparent electrode layer has a main thickness portion containing at least one of tin oxide and indium tin oxide as a main component;
A zinc oxide coating layer having a thickness in the range of 0 to 500 nm. 2. The integrated thin-film solar cell according to claim 1, wherein a crystalline semiconductor layer included in said semiconductor photoelectric conversion unit layer is grown in contact with said zinc oxide coating layer.