JPS61160980A - Manufacture of solar cell - Google Patents

Abstract

PURPOSE:To improve characteristics of solar cells such as open voltage, short- circuit current, and curve factor, by a method wherein hydrogen plasma treatment is carried out after formation of a print-calcined electrode. CONSTITUTION:After chemical polishing, an Si substrate 1 is rinsed and dried; then, an organic solution containing Ti and P is applied as the dopant diffusing solution and diffused by heating. The applied film coats the surface of the Si substrate 1 as a reflection-preventing film 2, and an N<+> diffused layer 3 is formed in the substrate 1. Next, an electrode 4 is print-calcined on the other surface of the substrate 1, and electrode 5 on the film 2, thus obtaining the structure of the titled element. This solar cell 11 is interposed between an electrode plate 13 and an opposite electrode plate 15 in the hydrogen plasma treatment apparatus, and hydrogen gas is introduced under evacuation inside the chamber. Then, plasma treatment is carried out in the hydrogen gas by supplying high frequency current across electrode terminals A, B.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing a solar cell with good device characteristics.
In particular, it relates to manufacturing technology for efficiently manufacturing polycrystalline or amorphous solar cells by introducing hydrogen plasma treatment.

<Conventional techniques and their problems> Conventionally commonly used solar cell element manufacturing methods include forming p-n junctions using a coating diffusion method and forming metal electrodes using a printing and baking method. A combination of these methods is often used. Among them, one of the low-cost and highly efficient methods is to apply a solution for dopant diffusion on the element substrate and then leave the coating film to be reused as an anti-reflection film when the element is used. A widely used manufacturing method is to form a solar cell by printing a paste material containing silver or the like as a main component thereon and firing it to form electrodes. However, when devices are formed using this method on, for example, a polycrystalline silicon substrate, device characteristics may deteriorate compared to when a single crystal substrate is used. The reason for this is that the electrical conductivity at the contact area between the printed and fired electrode and the polycrystalline silicon substrate is affected by the crystal grain size and crystal plane orientation of the substrate. This is thought to be due to variations in the fill factor, in particular.

A polycrystalline silicon substrate has irregular crystal grain sizes and crystal plane orientations, and therefore, the diode characteristics of the crystal grain boundaries at the contact portion between the diffusion surface of the polycrystalline silicon substrate and the electrode are poor, and the electrical conductivity is also nonuniform. For this reason, it becomes difficult to set the solar cell characteristics such as open circuit voltage, short circuit current, and fill factor to values that satisfy the solar cell characteristics. In order to improve solar cell characteristics, it is necessary to improve the electrical characteristics at the contact area between the polycrystalline silicon substrate and the printed and fired electrode.

Means for Solving the Problems> In order to solve the above-mentioned problems, the present invention aims to solve the above-mentioned problems by applying a dopant diffusion solution to a semiconductor substrate for manufacturing a solar cell element and performing a diffusion process, and then applying a dopant diffusion solution to a semiconductor substrate for manufacturing a solar cell element. The coating film is used as an antireflection film, and a metal paste is deposited on this film and printed and fired to form an electrode, and then a solar cell is produced by further performing hydrogen plasma treatment in a vacuum. .

By adding hydrogen plasma treatment in a vacuum, the device characteristics such as open circuit voltage and fill factor of the obtained solar cell are improved, and a solar cell with high practical value can be manufactured.

Note that a polycrystalline substrate or an amorphous substrate can be used as the semiconductor substrate, and by diffusing a dopant from a dopant diffusion solution into the semiconductor substrate set to be p-type or n-type to form a diffusion region of opposite polarity. ,
A p-n junction, p-1-n junction, etc. for obtaining an electromotive force can be obtained.

After forming the printed and fired electrode, by performing hydrogen plasma treatment in vacuum, hydrogen single atoms or molecules pass through the electrode part and the antireflection film part, and form the crystal grain boundaries on the diffusion surface of the semiconductor substrate. The diode properties are improved and the electrical conductivity between the electrode and the diffusion layer is improved by the intervention of hydrogen at the contact between the electrode and the diffusion layer, especially in the boundary region with the anti-reflection coating. As a result, deterioration in device characteristics caused by irregularities in crystal grain size and crystal plane orientation is compensated for, and the fill factor, open circuit voltage, etc. of the resulting solar cell can be maintained at good levels.

<Example> FIG. 1 is a cross-sectional configuration diagram of a solar cell element for explaining one example of the present invention. FIG. 2 is a schematic diagram of a hydrogen plasma treatment apparatus used to improve the characteristics of the solar cell element shown in FIG. 1.

A long crystalline silicon substrate l is used as a semiconductor substrate for producing a solar cell element. The silicon substrate 1 used has, for example, a specific resistance of 1 to 8 Ω-1 and a thickness of about 0.4 wm.

After chemically polishing the silicon substrate l with a polishing solution such as fluoro-nitric acid, it is washed with water and dried, and titanium (T) is added as a solution for dopant diffusion.
i) and an organic solution containing phosphorus (t) on a silicon substrate l.
Coat on one side of the paper using a spin method, etc. Next, the silicon substrate l having the coating film of this organic solution was heated to 900°C to 1000°C.
The Ti and P dopants are diffused from the coating film into the silicon substrate 1 by heating at a certain temperature. The coating film is solidified by this heat treatment and coats the surface of the silicon substrate 1 as an antireflection film 2. Further, an n10 diffusion layer 3 is formed in the silicon substrate 1. Next, a silver (Ag)-aluminum (A/) paste is printed and fired on the other surface of the silicon substrate 1 to form the electrode 4 on the back side. Further, an Ag paste is printed and fired on the antireflection film 2 by screen printing or the like to form the electrode 5 on the light receiving surface side. In this case, the Ag paste on the anti-reflection film 2 penetrates through the anti-reflection film 2 and comes into direct contact with the n+ diffusion layer 3. Through the above steps, the solar cell element structure shown in FIG. 1 is obtained.

By connecting both electrodes 4 and 5 to an electromotive force detection system and irradiating light with the antireflection film 2 side as a light receiving surface, the electromotive force generated within the solar cell element is detected. It is determined whether the characteristics of the solar cell element obtained by this electromotive force detection are good or bad. The anti-reflection film 2 has the function of suppressing the scattered reflection of the irradiated light on the light receiving surface and effectively introducing the irradiated light into the inside of the element, thereby improving the photoelectric conversion efficiency.

The solar cell elements judged to be good are inserted into a hydrogen plasma processing apparatus as shown in FIG. 2, and subjected to hydrogen plasma processing. That is, the solar cell element 11 is placed on the electrode plate 13 in which the heating element 12 is built in the chamber.
3 is adjusted to an appropriate temperature within a range of approximately 100° C. to 400° C. by controlling the amount of current flowing to the heating element 12 via the external lead wire 14. Directly above the electrode plate 13, a counter electrode plate 15 is arranged parallel to the electrode plate ]3.
Therefore, the solar cell element 11 has an electrode plate 18 and a counter electrode plate 15.
It will be interposed between. Both the electrode plate 13 and the counter electrode plate 15 are taken out to the outside as electrode terminals A and B, respectively, while being electrically insulated from the chamber. The inside of the chamber is evacuated through an exhaust pipe 16 and set to a vacuum of 1×1O=Torr or less. During plasma processing, hydrogen gas is introduced through the gas introduction pipe 17 at a rate of about 50-200 m/min in this vacuum state, and by adjusting the exhaust speed, the pressure inside the chamber is reduced to 0.5-20 m/min. Maintain it within a range of about .0 Torr.

Next, a high frequency current (1~50MHz) is applied between electrode terminals A and B.
supply. In this case, the power is 10 to 100W/10α
Angle range. Note that a DC voltage may be applied instead of the high frequency current. This state is maintained for 5 to 60 minutes to perform plasma treatment in hydrogen gas. After the plasma treatment has been completed, the solar cell element is taken out of the chamber and its characteristics are examined.

FIG. 3 is a characteristic explanatory diagram showing the operating characteristics of the solar cell element. The characteristic curve / in the figure shows the case where a single crystal silicon substrate is used, j2 shows the case where a polycrystalline silicon substrate is used and no hydrogen plasma treatment is performed, and j3 shows the case where hydrogen plasma treatment corresponding to the above example is performed. The characteristics of the case are shown below. In addition, the points I) 1 + 2 + p3 are the above characteristic curve '1, respectively.
, '2 +18. The quality of the characteristics of a solar cell element is determined by the open circuit voltage vt +''2 +v3 and the short circuit current!1 +$2 +$8 (Vt IV2+■3 and '1 +12 +18 are the characteristic curves ll, respectively.

12 + 13) is large and at the same time its fill factor is large, the maximum output point pl, p2 + p
It is determined by the size of 3. When a polycrystalline substrate is used, as shown by a characteristic curve 12, the open circuit voltage v2 and the short circuit current 12 are lowered, and at the same time, the fill factor is also significantly lowered, as compared to the case where a single crystalline substrate is used. However, by adding the hydrogen plasma treatment shown in the above example, the characteristic curve I! As shown by 8, the open circuit voltage v3 is increased and the fill factor is also significantly improved. For example, it has been confirmed that for a solar cell element with characteristic curve t2 whose photoelectric conversion efficiency is around 6x, the photoelectric conversion efficiency can be improved to around 10x by adding hydrogen plasma treatment to make a solar cell element with characteristic curve 13. It was done. By applying hydrogen plasma treatment, the first
Hydrogen atoms or hydrogen molecules pass through the electrode 5 and antireflection film 2 of the solar cell element shown in the figure, and the diode characteristics of the polycrystalline silicon substrate and the ohmic characteristics of the electrode 5 and the n-diffusion layer 3 are determined by the electrode 5. n has the effect of effectively improving the area where the three regions of the diffusion layer 32 and the anti-reflection film 2 are in contact;
This improves device characteristics.

Incidentally, in the above example, a case was explained in which a p-type child crystalline silicon substrate was used as a semiconductor substrate for solar cell production.
The present invention is not limited to this, and an amorphous substrate made of other materials can be used.

<Effects of the Invention> As explained in detail above, according to the present invention, the device characteristics expressed by the open circuit voltage, fill factor, etc. of the manufactured solar cell are improved, and high photoelectric conversion efficiency can be obtained.

In addition, the present invention is suitable for mass production, and it is only necessary to select devices with good characteristics after electrode formation and perform hydrogen plasma treatment, making it possible to establish a highly efficient production line.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram of a solar cell element for explaining one embodiment of the present invention. FIG. 2 is a schematic diagram of a hydrogen plasma processing apparatus used for the solar cell element shown in FIG. 1. FIG. 3 is a characteristic explanatory diagram showing the operating characteristics of the solar cell element. 1... Silicon substrate, 2... Antireflection film, 3...
n+ diffusion layer, 4.5... Electrode, 11... Solar cell element, 13... Electrode plate, 15... Counter electrode plate, 16...
...Exhaust pipe, 17...Gas introduction pipe.

Claims (1)

[Claims] 1. A dopant is added to a semiconductor substrate to form a photovoltaic junction, and a patterned electrode is formed on the light-receiving surface side of the semiconductor substrate, followed by hydrogen plasma treatment. Method of manufacturing solar cells. 2. Claim 1 in which the semiconductor substrate is a polycrystalline substrate
2. Method for manufacturing a solar cell as described in Section 1. 3. The method for manufacturing a solar cell according to claim 1, wherein the semiconductor substrate is an amorphous substrate. 4. The method for manufacturing a solar cell according to claim 1, wherein the light-receiving surface is coated with an antireflection film.