KR100374811B1 - Process for preparing buried contact solar cell - Google Patents

Abstract

PURPOSE: A process for preparing buried contact solar cell(BCSC) having low shading loss and electric power loss, thereby having excellent energy conversion efficiency, is provided. CONSTITUTION: The process for preparing buried contact solar cell comprises the steps of texturing the p-type semiconductor substrate(1) to form a pyramid structure on the front and rear surfaces of the substrate(1); diffusing an emitter to the substrate(1) to form p-n bonding; forming an oxide layer(3) on the front surface of the substrate(1); forming grooves on the substrate(1); doping the grooves with n-type impurities; vapor depositing conductive materials on the rear surface of the substrate(1) and then sintering to form back electrode(4); electroless plating with nickel onto the grooves to form nickel plating layer; electroplating with copper on the nickel plating layer to form copper plating layer; and electroless plating with silver onto the copper plating layer to form silver plating layer, thereby forming front electrode(2).

Description

Manufacturing method of depressed electrode type solar cell

The present invention relates to a method of manufacturing a depression electrode type solar cell, and more particularly, to a method of manufacturing a depression electrode type solar cell in which efficiency is improved by forming a finger surface area to be proportional to a current density.

A solar cell uses a band gap, which is a unique property of a semiconductor, as an electromotive force, and is made by combining a p-type semiconductor and an n-type semiconductor. When light enters the portion where the p-type semiconductor and the n-type semiconductor are in contact (pn junction), negative charges (electrons) and positive charges (holes) are generated inside the semiconductor due to light energy.

The electrons and holes generated by the light energy are moved to the n-type semiconductor side and the p-type semiconductor side by the internal electric field, respectively, and are collected in the both electrode portions. When these two electrodes are connected by a lead wire, current flows and can be used as an external power source.

Therefore, it is possible to increase the efficiency of the battery by absorbing a lot of light to generate as much electrons and holes as possible, and to reduce the voltage drop as much as possible without losing the generated electrons and holes.

Solar cells can be divided into screen printing solar cells (SPSC) and buried contact solar cells (BCSC) according to the shape of the electrodes.

The SPSC is generally easy to manufacture, but the conversion efficiency of the cell is low due to reflection at the metal electrode, resistance caused by the backside current flow, and high recombination of carriers in the generally deeply-doped emitter region, It is bad.

On the other hand, in the BCSC, the metal electrode is formed in the recess deeply in the front surface of the semiconductor substrate, and the conversion efficiency is higher than that of the SPSC. Thus, BCSC cells will become the mainstream of future commercial solar cells.

1 is a diagram showing a structure of a conventional BCSC. In FIG. 1, reference numeral 1 denotes a p-type semiconductor substrate, 2 denotes a front electrode, 3 denotes an oxide film, and 4 denotes a rear electrode. Reference numeral 5 denotes a finger which serves to transport generated current to the electrode.

However, as shown in FIG. 1, it can be seen that the cross-sectional area of the conventional depressed electrode type solar cell is constant regardless of the density of the current flowing along the finger.

When the cross-sectional area of the finger is constant regardless of the current density, the voltage drop due to the resistance is small in a portion where the current density is small. However, since the density of the current carried along the finger increases as the portion approaches the electrode, A large voltage drop occurs and thus a large power loss is caused. Moreover, as the size of the battery increases, the current density becomes larger, so that the power loss is further increased.

In order to overcome this problem, it is necessary to increase the cross-sectional area of the finger. If the cross-sectional area of the battery increases, the shading loss increases and the energy conversion efficiency of the battery decreases.

Accordingly, the present inventors have found that by overcoming the above-described problems and adjusting the cross-sectional area of the finger according to the current density, the shading loss and the power loss can be minimized to maximize the energy conversion efficiency of the battery. A depressed electrode type solar cell having a triangular finger has been proposed.

FIG. 2 shows a depressed electrode type solar cell in which the fingers have a triangular shape. The reference numerals in the drawings are as described above. As shown in FIG. 2, the fingers are in the form of a triangle whose cross-sectional area decreases as the distance from the electrode side increases.

However, in the conventional electroless plating method, the above-described triangular fingers could not be formed.

3, a conventional method of manufacturing a depression electrode type solar cell will be described.

First, texturing is performed to form a pyramid structure on the surface of the p-type semiconductor substrate (Fig. 3 (a)). An emitter is diffused to form a pn junction to form an n + layer, and then an oxidation process is performed to form an oxide film on the front and rear surfaces of the semiconductor substrate (FIG. 3B)). Next, a groove is deeply scribed into the entire surface of the semiconductor substrate using a laser or the like, and phosphorus is diffused to form an n ++ layer (FIG. 3C)). Next, aluminum is deposited on the rear surface of the substrate and then sintered to form a rear electrode (Fig. 3 (d)). The substrate is immersed in a nickel plating solution and the groove is electroless-plated with nickel (Fig. 3 (e)). Subsequently, the substrate is immersed in a copper plating solution, electroless-plated with copper, and immersed in a silver plating solution, followed by electroless plating with silver (FIG.

In the above-described conventional BCSC solar cell manufacturing method, the electroless plating method is employed at the time of forming the front electrode. However, according to the electroless plating method, there is a problem that the crossing area of the finger can not be controlled. That is, as shown in Fig. 1, the fingers 5 are formed with a constant cross-sectional area.

SUMMARY OF THE INVENTION The present invention provides a method of fabricating a solar cell having a shading loss and a low power loss and excellent energy conversion efficiency by forming fingers so that the cross sectional area of the finger is proportional to the current density increase.

1 is a perspective view of a conventional depressed electrode type solar cell.

2 is a perspective view of a depression electrode type solar cell according to the present invention.

FIG. 3 sequentially shows a method of manufacturing a conventional depressed electrode type solar cell.

FIG. 4 illustrates an electroplating apparatus used for forming a copper plating layer in the manufacture of a depression electrode type solar cell according to the present invention.

Description of the Related Art [0002]

1. p-type semiconductor substrate 2. front electrode

3. Oxide film 4. Rear electrode

5. Finger

The present invention provides a method of fabricating a semiconductor device, the method comprising: forming a pyramid structure on a front surface and a rear surface of a substrate by texturing a p-type semiconductor substrate; Diffusing an emitter to the semiconductor substrate to form a p-n junction; Forming an oxide film on the entire surface of the semiconductor substrate; Forming a groove in the semiconductor substrate; Doping the groove with an n-type impurity; Depositing a conductive material on the rear surface of the semiconductor substrate, and then sintering the conductive material to form a rear electrode; Electroless plating nickel in the groove to form a nickel plating layer; Electroplating copper on the nickel plating layer to form a copper plating layer; And forming a front electrode by electroless plating silver on the copper plating layer to form a silver plating layer on the copper plating layer.

In the method of manufacturing a depression electrode type solar cell according to the present invention, the nickel plating layer is formed by immersing the substrate in a plating solution and electroless plating at 350 to 400 DEG C under a nitrogen atmosphere for 10 to 20 minutes, and its thickness is 0.8 to 1.2 Mu m.

The copper plating layer is formed by placing a substrate in a copper electrolyte bath, connecting electrodes to the substrate, and then electroplating while adjusting the amount of current in the range of 0.5 to 2 A. At this time, the amount of current is initially reduced and then gradually increased. When the copper plating layer is formed by the electroplating method, the cross-sectional area of the finger decreases as the distance from the electrode portion decreases, so that the finger has a triangular shape.

FIG. 4 illustrates an electroplating apparatus used for forming a copper plating layer in the manufacture of a depression electrode type solar cell according to the present invention.

As shown in FIG. 4, a substrate is immersed in a copper electrolyte bath, and a voltage is applied to the entire surface of the substrate while irradiating a light source to fill the inside of the groove formed on the substrate with copper. When the voltage is applied, the cross-sectional area of the finger can be adjusted by controlling the amount of current.

The depressed electrode type solar cell manufactured according to the present invention can reduce the surface area of the finger by a factor of 2 by plating the finger using the electroplating method, and can significantly reduce the voltage loss due to the increase of the current density, The shading loss reduction effect can be obtained. Therefore, the depression electrode type solar cell according to the present invention has excellent energy conversion efficiency.

Claims (4)

a) forming a pyramid structure on the front and back surfaces of the substrate by texturing the p-type semiconductor substrate; b) diffusing an emitter to the semiconductor substrate to form a p-n junction; c) forming an oxide film on the entire surface of the semiconductor substrate; d) forming a groove in the semiconductor substrate; e) doping the trench with an n-type impurity; f) depositing a conductive material on the rear surface of the semiconductor substrate and then sintering to form a rear electrode; g) electroless plating of nickel in the groove to form a nickel plated layer; h) electroplating copper on the nickel plating layer to form a copper plating layer; And and i) forming a silver plating layer by electroless plating silver on the copper plating layer to form a front electrode. The method of claim 1, wherein the electroless plating is performed in a nitrogen atmosphere at 350 to 400 ° C for 10 to 20 minutes in step g). The method according to claim 1, wherein the thickness of the nickel plating layer is 0.8 to 1.2 탆. The method according to claim 1, wherein the amount of current during the electroplating in step h) is adjusted so as to gradually increase in a range of 0.5 to 2A.