JPH09191118A - Fabrication of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the fabrication process of solar cell by forming a coating layer of organic Ti compound containing phosphor on the surface of a substrate and an Al layer on the rear and performing thermal drive-in diffusion on the opposite sides thereby forming an antireflection film of TiO2 and a field layer simultaneously on the surface and rear of substrate, respectively. SOLUTION: A coating layer 3 of organic Ti compound containing phosphor is formed on the surface of an Si substrate 1 and then it is heated and dried. An Al layer 6 is formed on the rear by vacuum deposition. The substrate 1 is then set in a near infrared lamp heating furnace and a heat cycle is started to perform drive-in diffusion simultaneously on the opposite sides thus forming a bond (n+) and an antireflection film 4 of TiO2 on the surface while a field layer (p+) 5 on the rear, respectively. Subsequently, the surface is coated with a silver paste 9 containing n-type dopant while a silver paste 10 containing no dopant is printed on the rear and dried. Finally, it is fired and surface and rear electrodes 7, 8 are formed along with a heavily doped diffusion layer (n+1) 20 and then both electrodes 7, 8 coated with solder thus obtaining a solar cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low cost and highly efficient method for manufacturing a solar cell by a simple manufacturing process.

[0002]

2. Description of the Related Art FIGS. 2A to 2H show a conventional method for manufacturing a solar cell. To explain this, (A): p-type silicon substrate (electrical resistance 1 Ω · cm, thickness 350
μm) 11 is prepared, anisotropic etching is performed with an alkaline solution such as NaOH for the purpose of removing the surface strained layer at the time of slicing and texture processing, and then NH ₄ OH / H ₂ O ₂ / H ₂ O solution etc. The silicon substrate 11 is washed and spin-dried. (B): The silicon substrate 11 is set in a heat treatment furnace, and a bond (n +) 12 is formed by POCl ₃ thermal diffusion (850 ° C., 30 minutes). (C): Mask the resist 19 by screen printing on the surface. (D): Unnecessary bonding layer (n +) 12 formed on the back surface is HF / HNO
Remove using ₃ solution or NaOH solution. (E): The resist 19 is removed with an organic solvent, and the silicon substrate 1
Wash and spin dry. (F): TiO ₂ antireflection film 14 is formed on the surface by atmospheric pressure CVD. (G): Aluminum paste 16 by screen printing on the back side
Is printed on the entire surface and dried, then baked in a belt furnace (750
Then, the back surface electric field layer (p +) 15 is formed. (H): Silver paste is printed on both sides by screen printing and baked in a belt furnace to form electrodes 17 and 18. The surface silver electrode is optimized for firing conditions (650 ° C., 10 minutes) so that electrical contact can be obtained by fire-through the TiO ₂ antireflection film 14. Next, Sn / Pb / Ag solder coating is applied to the double-sided silver electrodes for the purpose of reducing the resistance of the electrode parts and connecting the solar cells.

[0003]

However, in the conventional method for manufacturing a solar cell shown in FIG. 2, it is difficult to manufacture a low-cost and high-efficiency solar cell by a simple process due to the following problems. is there. The reasons are: (1) A resist treatment step is required to remove the bonding layer (n +) formed on the back surface, which causes an increase in manufacturing cost and a decrease in productivity. (2) The heat treatment process for forming the junction (n +), the antireflection film, and the back surface electric field layer (p +) is a separate batch process, and the number of processes is large. As with (1), sufficient cost reduction and productivity can be achieved. Hard to improve. (3) The back surface field layer (p +) can be formed by printing the aluminum paste thickly on the entire surface and firing it without firing to reduce the back surface recombination rate.
When the substrate thickness is made thinner than μm, the manufacturing yield is expected to decrease due to warpage and damage. For this reason, there is a demand for a forming method which replaces the conventional back surface field layer (p +) formation by aluminum paste printing and firing. (4) Calculations predict that in order to realize a high-efficiency solar cell, it is important not only to reduce the back surface recombination rate by forming the back surface electric field layer (p +) but also to reduce the recombination rate below the front surface electrode. Has been done. For this purpose, it is necessary to form a high-concentration diffusion layer (n ++) in the lower part of the front surface electrode as well as the back surface electric field layer (p +), but in the case of commercially available joint (n +) formation, the surface has a uniform concentration profile. However, there is a problem that a sufficient reduction of the recombination rate cannot be obtained. On the other hand, although the improvement of the efficiency of the solar cell is recognized in the bond in which the high-concentration diffusion layer (n ++) is selectively formed only in the lower part of the electrode, the number of photolithography processes and thermal diffusion treatment processes is increased, which is extremely expensive. There is a problem with the manufacturing method.

[0004]

The present invention relates to a method of manufacturing a solar cell which solves the above-mentioned problems.
In the method of manufacturing a solar cell, (1) an organotitanium compound coating layer containing phosphorus / dopant is formed on the surface of a p-type silicon substrate, an aluminum layer is formed on the back surface, and the silicon is then heated in a near infrared lamp heating furnace. Drive-in diffusion is performed on both sides of the substrate to form an n + bonding layer and TiO _{2 on} the surface of the silicon substrate.
A step of simultaneously forming an electric field layer (p +) on the back surface of the antireflection film, and / or (2) including a Sb alloy dopant for selective diffusion under the electrode on the TiO ₂ antireflection film side of the surface of the p-type silicon substrate. After forming a silver paste coating layer and a silver paste coating layer on the back surface side of the electric field layer (p +), the silicon substrate is baked in a near infrared lamp heating furnace to simultaneously form silver electrodes on both sides. The gist of the invention is a method of manufacturing a solar cell, which includes the steps of:

In view of the above problems, the present invention eliminates (1) the resist treatment step in the solar cell manufacturing process, and (2) the junction (n +), the antireflection film, and the back surface electric field layer (p +). ) Are simultaneously formed by one heat treatment, and (3) a high-concentration diffusion layer (n ++) is simultaneously formed under the electrode when the surface silver electrode is formed, thereby reducing the recombination rate on the surface. It is intended to provide a method for manufacturing a solar cell which has a simple manufacturing process, is low in cost, and has high efficiency.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The steps (1) and (2) of the method for manufacturing a solar cell of the present invention will be described below. Regarding the process of forming the bonding layer (n +) and the TiO ₂ antireflection film on the front surface of the silicon substrate in the step (1) and the electric field layer (p +) on the rear surface at the same time, the p-type silicon substrate has a thickness of 0.1 to 0.4 mm. The one having an electric resistance of 1 to 10 Ω · cm is preferable, and the one whose surface is textured by a known method is preferable. The organotitanium compound coating layer containing phosphorus / dopant is applied by a method such as spin coating, and the thickness is preferably 0.1 to 0.2 μm. As phosphorus / dopant, P ₂ O ₅ , SiP ₂ O ₇ , CeP ₅ O _{14 and the} like are exemplified, and a known organic titanium compound may be used, and examples thereof include an organic titanium compound disclosed in JP-A-60-140880 or a composition of an organic titanium compound and an organic tin compound. . In the present invention, it is preferable to use an organic titanium compound solution containing a phosphorus / dopant as a coating agent, and examples of the solvent include organic solvents such as various alcohols, esters and ketones, and the solution viscosity is suitable for spin coating. 10 to 30 cP is good. The aluminum layer on the back side is formed by vacuum evaporation or sputtering and has a thickness of 0.5.
~ 3 μm is good. The method of drive-in diffusion is performed to a heat cycle in an atmosphere under the following conditions of _{N 2 / O 2 (3%} ) using near-infrared lamp heating furnace, performing duplex simultaneous drive-in diffusion. Thermal cycle conditions are temperature rising rate of 10 to 50 ℃ / sec.
The temperature is raised to 850 to 950 ° C, kept at that temperature for 1 to 2 minutes, and then cooled to 800 ° C at a cooling rate of 0.5 to 2 ° C / sec to perform natural cooling.

Regarding the step of simultaneously forming a double-sided silver electrode on the surface of the silicon substrate in the step (2), Ge-Sb, Sn-Sb, Ge-S are used as Sb alloy dopants for selective diffusion under the electrodes.
Examples include n-Sb. The silver paste layer on the surface side is applied by a method such as screen printing, and the thickness is preferably 10 to 20 μm.
A silver paste layer is similarly formed on the back side. The silver paste layers on both sides may be fired in a near infrared lamp heating furnace in a dry air atmosphere at a temperature of 600 to 700 ° C. for 5 to 20 minutes.

According to the present invention, the organic titanium compound coating agent is spin-coated on the front surface and Al is formed on the rear surface by vacuum deposition or sputtering, and then heat treatment is performed, so that the bonding layer (n +) is formed on the rear surface as in the conventional thermal diffusion method. The advantage is that the resist process can be omitted without the formation of the film and the titanium compound coating film on the front surface and the aluminum film on the back surface prevent mutual cross-contamination even if simultaneous heat treatment is performed. There is. Furthermore, since a coating material containing phosphorus / dopant such as P ₂ O _{5 in an} organotitanium compound solution is used as a bonding (n +) forming agent on the surface, this coating film after heat treatment has TiO ₂ reflection. Effectively acts as a preventive film.

In forming the back surface electric field layer (p +), aluminum is present in the form of particles in the conventional aluminum paste firing method. Therefore, in order to obtain a sufficient electric field effect, the thickness of the aluminum paste is 20 to 40 μm. Therefore, in the production of thin solar cells, the reduction in production yield due to warpage or damage is a problem. On the other hand, when aluminum is formed by vacuum vapor deposition or sputtering and then alloyed at the melting point (580 ° C) or higher of aluminum, the aluminum is Al-Si uniformly over the entire surface.
By alloying, a back surface field effect equivalent to that of the conventional firing method can be obtained even with an extremely thin film thickness of about 2 μm. Therefore, when this method is applied to a thin silicon substrate, a good manufacturing yield can be expected.

Next, in realizing a high-efficiency solar cell, it is important not only to reduce the back surface recombination rate by the back surface field layer, but also to reduce the front surface recombination rate. For this purpose, it is necessary to make the surface bonding layer (n +) low in concentration, but if the concentration is made evenly low, (1) increase in electrode contact resistance loss, (2) recombination at the bottom of the electrode Efficiency cannot be expected to increase due to increased speed. In the present invention, in the silver paste n
A high-concentration diffusion layer (n ++) is selectively formed under the electrode by including Sb alloy that is a type dopant, and when the surface bonding layer (n +) is formed under the optimum low-concentration and high-sheet forming conditions. However, since the recombination rate at the lower part of the electrode does not increase, and because the lower part of the electrode diffuses under high-concentration and low-sheet conditions, it is possible to keep the contact resistance with the electrode low enough. By the simple process called the method, it can be expected to manufacture a high-efficiency solar cell similar to the process using photolithography.

[0011]

【Example】

Examples and Comparative Examples Examples and comparative examples will be described below, but the present invention is not limited thereto. 1 (a) to 1 (f) show an example of the manufacturing process of the solar cell of the present invention and the performance of the manufactured solar cell. In the present invention, the step (1) was performed as follows. (A): p-type silicon substrate 1 (electrical resistance 1Ω · cm, thickness 20
0 μm) is prepared, anisotropic etching is carried out with an alkaline solution such as NaOH for the purpose of removing the surface strain layer at the time of slicing and texture processing, and silicon is used with NH ₄ OH / H ₂ O ₂ / H ₂ O solution. The substrate 1 is washed and spin dried. (B): An organic Ti compound solution coating agent containing P ₂ O ₅ was applied to the surface of the silicon substrate 1 by spin coating to a thickness of 0.1 μm.
The organic Ti compound coating layer 3 is formed and dried at 120 ° C. for 10 minutes. (C): An aluminum layer 6 is formed on the back surface by vacuum vapor deposition or sputtering to a thickness of 1 to 2 μm. (D): The above-mentioned silicon substrate 1 was set in a near-infrared lamp heating furnace, and thermal cycling was performed under the following conditions to perform both-side simultaneous drive-in diffusion to bond (n +) 2 and TiO ₂ antireflection film 4 to the surface. An electric field layer (p +) 5 is formed on the back surface. The heat cycle condition is that the temperature is raised to 850 to 950 ° C at a heating rate of 10 to 50 ° C / sec, kept at the same temperature for 1 to 2 minutes, and then cooled at a rate of 0.5 to
After cooling to 800 ° C at 2 ° C / sec, perform natural cooling.
Then, the step (2) of the present invention was performed as follows. (E): A silver paste 9 containing an Sn-Sb alloy, which is an n-type dopant, is applied on the surface by screen printing to a thickness of 20 μm and dried at 120 ° C. for 10 minutes. In addition, similarly Sn-S on the back side
b Alloy-free silver paste 10 is printed and dried. (F): The silicon substrate 1 having silver pastes 9 and 10 printed on both sides is passed through a belt furnace and baked at 650 ° C. for 10 minutes to form the front electrode 7, the high-concentration diffusion layer (n ++) 20 and the back electrode 8. . Then, Sn / Pb / Ag based solder coating is applied to the electrodes 7 and 8 to complete the solar cell.

Solar simulator (conditions AM1.5, 25
When the short circuit current, release voltage, fill factor and conversion efficiency of the solar cell of the present invention produced by the method of FIG. As a comparative example, a solar cell manufactured by the conventional method shown in FIG. 2 was measured in the same manner, and the results are shown in Table 1.

[0013]

[Table 1]

[0014]

According to the present invention, since the junction (n +), the antireflection film, and the back surface electric field layer (p +) can be simultaneously formed on only one side, the opposite surface can be removed as in the conventional case. Since the resist processing step is unnecessary and the manufacturing process can be significantly shortened, it is possible to reduce the manufacturing cost and improve the productivity. Also, by simultaneously forming a high-concentration diffusion layer (n ++) under the surface silver electrode during firing, it is possible to reduce the surface recombination rate equivalent to that produced by a high-cost manufacturing process using a photolithography process. ,
As a result, it is possible to manufacture a high-efficiency solar cell by a low cost and simple manufacturing method as compared with the conventional manufacturing method.

[Brief description of the drawings]

1A to 1F show an example of a series of manufacturing steps in a method for manufacturing a solar cell according to the present invention.

2 (A) to (H) show a series of manufacturing steps in a conventional method for manufacturing a solar cell.

[Explanation of symbols]

1, 11 ... Silicon substrate 2, 12 ... Bonding (n +) 3 ... Organic titanium compound coating layer 4, 14 ... TiO ₂ antireflection film 5, 15 ... Electric field layer (p +) 6, 16 ... Aluminum layer 7, 17 ... Surface Electrodes 8, 18 ... Back electrode 9 ... Sb alloy-containing silver paste 10 ... Silver paste 19 ... Resist 20 ... High concentration diffusion layer (n ++)

Claims (1)

[Claims] 1. A method of manufacturing a solar cell, comprising: (1) forming a coating layer of an organotitanium compound containing phosphorus / dopant on the surface of a p-type silicon substrate, forming an aluminum layer on the back surface thereof, and then forming a near infrared lamp. Drive-in diffusing both surfaces of the silicon substrate in a heating furnace to simultaneously form an n + junction layer and a TiO ₂ antireflection film on the front surface of the silicon substrate, and an electric field layer (p +) on the back surface, and / or (2 ) A silver paste coating layer containing Sb alloy dopant for selective diffusion in the lower part of the electrode is formed on the TiO ₂ antireflection film side of the surface of the p-type silicon substrate, and a silver paste coating layer is formed on the electric field layer (p +) side of the back surface. After the formation, a step of firing the silicon substrate in a near-infrared lamp heating furnace to simultaneously form silver electrodes on both sides, a method of manufacturing a solar cell.