JPS6113395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing method for increasing the efficiency of solar cells, particularly solar cells using low-cost polycrystalline substrates.

Recently, attempts have been made to use polycrystalline substrates in place of conventional single-crystalline substrates in order to significantly reduce the cost of solar cells.

A polycrystalline substrate formed by a ribbon crystal growth method, a casting method, or the like is used for this purpose. Regarding the ribbon crystal growth method, there is no cutting loss to make it into a plate shape, and regarding the casting method, the growth rate is fast and it is suitable for mass production, and the rectangular substrate is suitable for solar cells. This is because it is suitable for reducing costs because it can form a .

On the other hand, various methods for increasing the efficiency of solar power generation using conventional single-crystal silicon substrates have been developed. One example is CNR solar cells. CNR stands for Comsat Non-Reflctire solar cell, and it was announced in 1974 as the most improved new cell, with an efficiency of over 15% in AMO and AMI
A high conversion efficiency of over 18% was achieved. The anti-reflection coating applied to the mirror-polished silicon surface is
Although reflection of light within a certain range of wavelengths is suppressed, reflection loss of approximately 7% over the entire wavelength range cannot be prevented. Therefore, as a method to reduce this loss, we formed unevenness consisting of countless microtetrahedra on the surface of a single crystal silicon substrate, and improved the light absorption rate by optically multiple reflection and refraction between the incident light and the pyramid surface of the surface. An attempt was made. Evenly fine particles are formed on the surface of a 100-sided single-crystal silicon substrate with good reproducibility.
Anisotropic etching technology that creates pyramidal irregularities with 111 planes is an important point in CNR cell fabrication technology. The size of the pyramid is extremely small, with both the height and the base being several micrometers. Solar cells with such a surface are also called textured surface cells.

However, when using a single crystal silicon substrate, the above-described anisotropic etching technique for creating a CNR cell cannot be used. In the case of a polycrystalline substrate, as shown in Figure 1, the crystal axes of each polycrystalline grain 2 are oriented in completely arbitrary directions, and cannot be aligned in 100 planes like in a polycrystalline substrate. It is. Therefore, until now, it has been considered very difficult to convert polycrystalline silicon solar cells into CNR cells. Although the cost of polycrystalline silicon solar cells can be significantly reduced, it has been considered difficult to achieve the same level of efficiency as single-crystalline cells.

The purpose of the present invention is to improve the above-mentioned problems of polycrystalline silicon solar cells, and to obtain highly efficient solar cells even when using a polycrystalline silicon substrate by making the surface a textured surface. The object of the present invention is to provide a manufacturing method that can be used.

The present invention forms countless minute eutectic liquid phases on the surface of a polycrystalline silicon substrate, and by the action of these eutectic liquid phases, unevenness is created on the surface of the polycrystalline substrate in the same way as a CNR cell, reducing reflection loss. The aim is to improve the efficiency of solar cells. The eutectic liquid phase can be formed, for example, by combinations such as aluminum-silicon, antimony-silicon, or tin-silicon. Taking the aluminum-silicon system as an example, the melting point of aluminum is 660℃,
Aluminum-silicon forms a eutectic liquid phase at temperatures above 577°C, and the eutectic reaction progresses until the concentration of silicon relative to aluminum reaches a certain constant value.
In other words, if aluminum metal is in contact with the silicon substrate surface at a certain thickness, this is 577
When heated above .degree. C., a eutectic liquid phase is formed on the surface of the silicon substrate, and the surface of the silicon substrate is corroded by this eutectic liquid phase. After the erosion has progressed to a certain extent, the eutectic liquid phase is removed and the silicon surface is exposed again. The problem is how to form countless minute metal particles on the surface of a silicon substrate. Judging from the size of the pyramid of the CNR cell, the size of the minute metal grains is probably about several μm square. Such minute shapes are usually formed by a photoresist method or the like. However, in a low-cost solar cell as in the case of the present invention, it seems difficult to use an expensive method such as the photoresist method. Therefore, an inexpensive method suitable for mass production is desirable. A spray method is one such method. This is the method used when applying paint, etc. Fortunately, aluminum has a melting point of 660.
Since the temperature is relatively low (°C), it is possible to spray minute droplets by considering the material of the spray nozzle.

When quartz was actually used as the nozzle material, the size of the droplets could be reduced to about several μm.

On the other hand, aluminum acts as a P-type impurity for silicon, so if an n-type substrate is used, aluminum will diffuse into the substrate during the formation of the eutectic liquid phase and form a P-n junction on the substrate surface. I can do it. That is, the present invention is characterized in that the formation of irregularities on the substrate surface by the eutectic liquid phase and the formation of a bond are performed in the same process.

Hereinafter, the present invention will be explained in detail using the drawings.

For example, when using n-type silicon formed by a casting method as a polycrystalline substrate, as shown in FIG. form 3. Next, such a polycrystalline substrate with aluminum metal grains is held at a high temperature to generate a eutectic liquid phase 4, and the silicon substrate is further corroded by this eutectic liquid phase, as shown in FIG. After sufficient erosion, if the eutectic layer 4 on the surface is removed using an appropriate etching solution, the surface will have countless fine irregularities as shown in FIG.
A solar cell substrate on which the junction 5 is formed is obtained.
Thereafter, a grid-like electrode metal is deposited on the front surface and an electrode metal is deposited on the back surface to form a solar cell. The above is a case where n-type polycrystalline silicon is used as a substrate,
Even when P-type silicon is used as a substrate, a solar cell can be produced in exactly the same manner by replacing the impurity with antimony, for example. In this way, high-efficiency solar cells similar to single-crystal CNR cells can be made using inexpensive polycrystalline silicon substrates.

Hereinafter, the present invention will be explained in detail according to Examples.

Example 1 The surface of an n-type polycrystalline silicon substrate doped with phosphorus as an impurity by the casting method and having a resistivity of 1.0 Ω-cm was wrapped with #1200 Kenma material. Aluminum melt is sprayed onto the surface of such a polycrystalline substrate using a quartz sprayer. The spray conditions were an average droplet diameter of 6 μm, a coating speed of 30 μm/mm, and a time of 6 seconds. As a result, on the surface of the polycrystalline substrate,
Aluminum metal grains with a diameter of several μm and an interparticle distance of several μm are formed. The polycrystalline substrate with aluminum metal grains formed on its surface in this way is held at 900° C. for 30 minutes in nitrogen gas to form irregularities on the surface and form a P-n junction. Thereafter, the eutectic layer formed on the surface was removed by etching with 10% dilute hydrofluoric acid, a grid-like electrode metal on the surface and an electrode metal on the back were deposited, and an antireflection film of Ta ₂ O ₅ was further formed on the surface. We fabricated a polycrystalline CNR type solar cell. The cell characteristics are AMI, open circuit voltage 0.57V,
The short-circuit current was 33 mA/cm ³ and the photoelectric conversion efficiency was 12%, which is very good compared to conventional polycrystalline cells, and comparable to expensive commercially available polycrystalline cells.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are diagrams for explaining the process of manufacturing a high-efficiency polycrystalline solar cell according to the present invention. In the figure, 1 is a polycrystalline silicon substrate, 2 is a polycrystalline grain, 3 is an aluminum metal grain, 4 is an aluminum-silicon eutectic liquid phase, and 5 is a Pn junction.

Claims (1)

[Claims] 1. A solar cell characterized in that in manufacturing a solar cell using a polycrystalline silicon substrate, countless minute eutectic liquid phases are formed on the surface of the polycrystalline substrate to make the substrate surface uneven and at the same time form a bond. manufacturing method.