JPH0730134A - Manufacture of solar cell - Google Patents

Abstract

PURPOSE:To provide a solar cell whose contact width with a conductive materuial used for series connection to a window layer is reduced by reducing a contact resistance with the conductive material used for series connection to the window layer and whose photoelectric conversion efficiency is high by increasing an effective light-receiving area in the solar cell which has the window layer on a light-transmitting substrate and which has a CdTe film as an optical absorption layer. CONSTITUTION:A CdS film 2 as a window layer and a CdTe film 3 as an optical absorption layer are laminated sequentially, a C film 4 as an acceptor for the CdTe film 3 is formed, and a YAG laser treatment is executed to the pattern separation part of the CdTe film 3 from the C film 4. Them protruding parts outside the prescribed pattern of the CdTe film 3 and the C film 4 and impurities on the surface of the window layer are removed simultaneously. Thereby, the contact width of the CdS film 2 with an AgIn film 5 can be reduced to about 1/3 as compared with that in conventional cases, the effective light-receiving area of a solar cell can be increased, and the solar cell of high efficiency can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solar cell, and more particularly to a cadmium telluride film (hereinafter referred to as C
The present invention relates to a method for manufacturing a solar cell using a dTe film) and a carbon film (hereinafter C film) obtained by applying, drying and sintering a carbon paste (hereinafter C paste) as an ohmic electrode.

[0002]

2. Description of the Related Art In recent years, as global environmental problems such as global warming due to carbon dioxide and destruction of the ozone layer have been highlighted, expectations for new energy development, especially for practical use of solar cells, have been increasing. . However, many problems still remain to be solved for the early commercialization of solar cells. In particular, improving the conversion efficiency of solar cells and reducing costs are important issues that cannot be avoided.

Under such circumstances, the CdS / CdTe solar cell has 1.4eV, which is close to the optimum forbidden band width as a light absorption layer.
CdTe is used, and the material used is also inexpensive, so it is highly expected as one of the favorite of low-cost and high-efficiency solar cells.

The CdS / CdTe solar cell manufacturing method includes:
Various methods are known, but there is a printing / sintering method as a method that can reduce the cost, and can easily increase the area and mass production.
The printing / sintering method uses inexpensive equipment, and solar cells already manufactured by the same method are widely used for calculators.

A CdS sintered film is formed on a supporting substrate according to Japanese Patent Laid-Open No. 2-177377, and TeCl is formed thereon.
CdTe paste added to CdTe powder with ₄ as a flux is screen-printed, dried, and fired in an inert gas atmosphere to form a CdTe sintered film, then a carbon film is formed on the CdTe sintered film, and CdS firing is performed. A method of manufacturing a photovoltaic element in which an electrode is formed on a conjunctiva and a carbon film is disclosed.

Below, CdS / by the conventional printing / sintering method is used.
A method for manufacturing a CdTe solar cell will be described.

The structure of the solar cell is glass / CdS film / Cd
It consists of a Te film / carbon electrode film / AgIn electrode film, and each film is formed by the following method.

(1) Formation of CdS Film 12% by weight of CdCl ₂ powder and an appropriate amount of propylene glycol are added to high-purity (5N) CdS powder having a particle diameter of 2 to 3 μm and kneaded to prepare a CdS paste. This paste is then printed on a borosilicate glass substrate.
This is dried at 120 ° C. for 1 hour, placed in an alumina firing case, covered with a firing lid having many small holes, and fired at 690 ° C. for 90 minutes in a nitrogen atmosphere belt furnace.

(2) Formation of CdTe Film Cd powder (5N) and Te powder (6N) are added in equimolar amounts and pulverized with water in a ball mill to a particle size of 1 μm or less. After drying, an appropriate amount of CdCl ₂ is added to this fine powder, and propylene glycol is kneaded as a binder to prepare a paste. Next, the paste is screen-printed on the CdS film, dried at 120 ° C. for 1 hour, and then baked at 600 ° C. to 700 ° C. for 1 hour using a predetermined container in the same manner as the CdS film to obtain a CdTe film.

(3) Carbon Electrode Film C paste containing a small amount of CuO is used for the electrode of CdTe. After printing this C paste on the CdTe film,
Drying is performed at 120 ° C. for 1 hour, and heat treatment is performed at 450 ° C. in a nitrogen atmosphere containing a slight amount of oxygen to form. A small amount of CuO makes the contact surface with CdTe a p ⁺ -CdTe layer, and enables good ohmic contact.

(4) AgIn electrode film For the electrodes of CdS, Ag paste containing In is used. After printing this Ag paste on the CdS film,
Allows good ohmic contact after drying for 1 hour.

[0012]

However, in the screen printing method, printing of CdTe paste and C paste,
At the time of drying, fine particles in the paste largely move, so that the paste protrudes outside the predetermined pattern. When trying to increase the effective area ratio of an integrated solar cell in which a large number of solar cell elements are connected in series on one substrate, this causes short circuits between solar cell elements and leakage of current, and 90%
It is difficult to achieve the above effective power generation area ratio. Further, when the solar cell elements are connected in series, the window layer and the carbon layer are electrically connected by a conductive material. However, impurities deposited on the surface of the window layer during the process up to CdTe firing may cause a difference between the window layer and the conductive material. It increases the resistance of ohmic contact and causes deterioration of solar cell performance.

The present invention solves such a conventional problem by effectively utilizing the characteristics of the conventional process to prevent short circuit between solar cell elements and leakage of current, and to prevent the shortage of the window layer and the conductive material. It is an object of the present invention to provide a method for manufacturing a solar cell capable of achieving a high effective power generation area ratio by lowering the resistance between solar cell elements by improving the ohmic contact.

[0014]

In order to achieve the above object, the first means of the method for manufacturing a solar cell according to the present invention separates into a predetermined pattern for making a serial connection on a transparent substrate. At least CdT as an absorption layer on the window layer formed by
After the e film is separated and formed into a predetermined pattern, a carbon film (hereinafter referred to as a C film) as an acceptor material and an ohmic electrode is separated and formed into a predetermined pattern, and the C film and the window layer are connected in series by a conductive material. A method of manufacturing a solar cell, which comprises applying a C powder mainly composed of a C powder and an organic solvent to form a C film, and then exposing the CdTe film and the C film outside a predetermined pattern and the surface of the window layer. This is a method in which the impurities precipitated in the above are removed by using a laser beam, followed by drying and firing.

The second means is to apply the C paste after coating and drying, perform laser treatment in the same manner as above, and then sinter, so that impurities protruding on the portion outside the predetermined pattern and on the surface of the window layer are irradiated with laser light. Is used to remove and then fire.

[0016]

According to the above method, the contact surface of the solar cell window layer is subjected to laser treatment, so that the CdTe paste and the C paste protrude outside the predetermined pattern at the time of printing and drying, resulting in short circuit between solar cell elements and generation of current. It is possible to prevent leakage and to achieve a high effective power generation area ratio. Furthermore, Cd, Te, CdCl on the window layer
_{When 2} is removed and a polycrystalline semiconductor such as CdS is used for the window layer, the boundaries between the crystals can be modified to improve the film quality itself of the window layer. As a result, it is a main factor of the contact resistance of the solar cell element. The contact width between a certain window layer and the AgIn film that is the electrode film thereof can be greatly reduced, and a highly efficient solar cell can be manufactured.

[0017]

The method for manufacturing a solar cell according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a CdS film 2 is formed as a window layer on a glass substrate 1 or a glass substrate (not shown) having a transparent electrode formed on the surface thereof, which is exactly the same as the conventional technique described above. The CdTe film 3 and the C
A film and further an AgIn film are formed. Normally, glass with a size of 35 cm x 35 cm or more is used as the substrate size, and C
Since the sheet resistance of the dS film 2 is 20 to 100 Ω / cm ² , and the width of the CdS film 2 of a single cell is not less than 5 mm, the efficiency is significantly reduced, and therefore it is necessary to connect in series. There are many systems that charge the battery, and for that reason it is necessary to connect in series. FIG. 2 shows the correlation between the width of the CdS film 2 and the efficiency.

A screen printing method is used as a method of forming the CdTe film 3 and the C film 4, and the CdTe paste and the C paste are 50 to 100 when the printing and drying are performed.
About 3 μm outside the predetermined pattern, and a thin protruding portion 7 of the CdTe film and a protruding portion 8 of the C film are formed on the CdS contact surface 6 as shown in FIG.
When the protruding portion 8 of the C film contacts the CdS contact surface 6, current leakage is caused, and when the protruding portion 7 of the CdTe film or the protruding portion 8 of the C film on both ends of the CdS contact surface 6 contacts, It becomes a short circuit between the elements. Further, even when the CdTe film 3 is baked on the CdS contact surface 6, a redeposited layer 9 of impurities of Cd, Te, CdCl ₂ or CdTe is generated, and a clean CdS contact surface 6 cannot be obtained, so that the CdS film 2 and its electrode film are not formed. A certain Ag
Good contact cannot be obtained unless the contact width 10 of the In film 5 is 0.3 mm or more.

In order to improve the above, as shown in FIG. 4, after the C film 4 is applied, or after the application and drying, the CdS contact surface 6 is formed.
YAG laser processing in Q switch output mode,
The protruding portion 7 of the CdTe film protruding outside the predetermined pattern on the CdS contact surface 6 shown in FIG. 3 and the protruding portion 8 of the C film and the impurities deposited on the CdS contact surface 6 during the firing of the CdTe film 3 are regenerated. The deposit layer 9 is removed. Next, the AgIn film 5 is formed by a known method. C
By subjecting the dS contact surface 6 to YAG laser treatment, the CdS contact width becomes 0.3 mm as shown in FIG.
Even if the thickness is reduced to 0.1 mm, the resistance is not significantly increased and the FF is not significantly decreased as in the conventional case.
With a contact width of 1 mm, it is possible to obtain a contact resistance as low as that of the conventional 0.3 mm. In other words, due to the reduction of the contact width, the portion of the solar cell that converts light into electricity increases and the cell connection portion decreases, so that the effective light receiving area can be increased, and as a result, the photoelectric conversion efficiency can be improved. Is possible.

[0021]

As is apparent from the above description, according to the method for manufacturing a solar cell of the present invention, a CdS film is formed as a window layer, a CdTe film is formed as a light absorption layer, and a C film is formed as an acceptor of the CdTe film. In the solar cell to be formed, after forming the C film, YA is applied to the CdS contact surface in the Q switch output mode.
By applying the G laser treatment, the CdTe paste and the C paste are prevented from causing a short circuit between solar cell elements and a leakage of current by removing a portion protruding out of a predetermined pattern at the time of printing and drying. When the area ratio can be achieved, impurities such as Cd, Te and CdCl ₂ on the CdS contact surface are removed and a polycrystalline semiconductor such as CdS is used as the window layer, the boundary between the crystals is modified. As a result, the window layer film quality itself can be improved, and as a result, the contact width between the window layer and the electrode film AgIn film, which is the main factor of the contact resistance of the solar cell element, can be significantly reduced, and a highly efficient solar cell can be manufactured. It is possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a solar cell after formation of a CdS film / CdTe film / C film / AgIn film in a method for manufacturing a solar cell according to an embodiment of the present invention.

FIG. 2 is a graph showing a correlation between the CdS film width and the photoelectric conversion efficiency of the solar cell in the method for manufacturing the solar cell according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a YA after forming a CdS film / CdTe film / C film / AgIn film in a method for manufacturing a solar cell according to an embodiment of the present invention.
Sectional view of the solar cell on the CdS contact surface of the solar cell before G laser processing

FIG. 4 is a cross-sectional view of a solar cell after laser treatment of the CdS contact surface of the solar cell in the method for manufacturing a solar cell according to an embodiment of the present invention.

FIG. 5 is a graph showing the correlation between the effective area ratio and the conversion efficiency with respect to the contact width between the CdS film and the AgIn film in the method for manufacturing a solar cell according to the embodiment of the present invention.

[Explanation of symbols]

 1 glass substrate 2 CdS film (window layer) 3 CdTe film 4 C film 5 AgIn film 6 CdS contact surface 7 protruding part of CdTe film 8 protruding part of C film 9 redeposition layer 10 contact width of CdS film and AgIn film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Murozono 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. After forming at least a cadmium telluride film as an absorption layer in a predetermined pattern on a window layer formed in a predetermined pattern to form a serial connection on a transparent substrate. A method of manufacturing a solar cell in which a carbon film is formed as an acceptor material and an ohmic electrode in a predetermined pattern separately, and the carbon film and the window layer are connected in series by a conductive material. After applying a carbon paste mainly composed of a powder and an organic solvent, the cadmium telluride film and the carbon film were removed from the predetermined pattern by using laser light to remove the protruding portion and impurities deposited on the surface of the window layer. A method for manufacturing a solar cell, which is followed by drying and firing. 2. After forming at least a cadmium telluride film as an absorption layer in a predetermined pattern on a window layer formed in a predetermined pattern to form a serial connection on a transparent substrate. A method of manufacturing a solar cell in which a carbon film is formed as an acceptor material and an ohmic electrode in a predetermined pattern separately, and the carbon film and the window layer are connected in series by a conductive material. A powder and a carbon paste mainly composed of an organic solvent are applied, and after drying, the cadmium telluride film and the carbon film are out of a predetermined pattern, and the impurities deposited on the protruding portion and the surface of the window layer are irradiated with laser light. A method for manufacturing a solar cell, which is fired after being removed. 3. The method for producing a solar cell according to claim 1, wherein the window layer is composed of a cadmium sulfide film only. 4. The method for producing a solar cell according to claim 1, wherein the window layer comprises two layers of a transparent conductive film and a cadmium sulfide film.