KR100863951B1 - Solar cell and fabrication method thereof - Google Patents

Abstract

The present invention relates to a high efficiency solar cell and a method of manufacturing the same. The purpose of the present invention is to manufacture a high efficiency solar cell having no impurities and preventing performance deterioration due to heat load at an improved process cost. To this end, in the present invention, a silicon layer doped with a metal and a metal layer containing a small amount of silicon are formed on the front surface of the silicon substrate by a solution growth method using a difference in the solid solution of silicon according to the temperature of the metal, and a front electrode is formed thereon. It is characterized by.

Solar cell, electrode, solution growth method

Description

Solar cell and fabrication method thereof

1 is a perspective view showing a high efficiency solar cell structure according to an embodiment of the present invention.

2 is a phase diagram of metal and silicon.

The present invention relates to a high efficiency solar cell and a method for manufacturing the same, and more particularly, to a method of forming a front electrode using a solution growth method.

In general, a solar cell has a pair of electrons and holes generated inside the semiconductor of the solar cell by light from outside, and electrons move to an n-type semiconductor by an electric field generated at a pn junction in the pair of electrons and holes. Moving to p-type semiconductors produces power.

In buried contact solar cell (BCSC), which is one of the high efficiency solar cell structure designed to improve the efficiency of conventional solar cell, the groove is formed on the front of the solar cell and the inside of the groove is filled with a conductive material. To form a metal electrode of the recessed shape.

In this way, if the metal electrode on the front surface is formed in the silicon substrate, the contact resistance is lower than that of the electrode on the silicon oxide film, and the electrode does not absorb sunlight as much as the area occupied by the upper surface of the substrate. Shading loss, which is caused by failure, can be reduced by 2-3%. Therefore, the solar cell of the recessed electrode structure is known to be suitable for high efficiency and low price of the solar cell.

Conventional techniques related to solar cells with recessed electrode structures include US Pat. Nos. 4,748,130 and 4,726,850. In these patents, grooves are first formed in the front surface of a p-type silicon substrate, and the phosphors are formed on the front surface of the p-type silicon substrate including the grooves. After doping (P) to form an n layer, an Al layer is formed on the back surface of the p-type silicon substrate to form a back electrode, and a high concentration impurity region is formed by doping phosphorus at a high concentration on the inner wall of the groove, followed by plating. Alternatively, the inside of the groove is filled with silver (Ag) by vacuum deposition or the like to form the front electrode in a recessed structure.

In the above manufacturing process, a high concentration of impurity regions are formed by doping phosphorus at a high concentration to form an ohmic contact between the front electrode and the silicon substrate. Go through the process.

However, the inflow of impurities from the furnace (furnace) may be promoted when the heat treatment at a high temperature, especially when using a polycrystalline silicon substrate has a problem that the performance of the solar cell is degraded due to excessive heat load.

The present invention is to solve the problems as described above, the object is to produce a high efficiency solar cell with low process cost improved efficiency by preventing impurities and performance degradation due to heat load.

In order to achieve the object as described above, in the present invention, a silicon layer doped with a metal and a metal layer containing a small amount of silicon are formed on the entire surface of the silicon substrate by a solution growth method using a difference in the solid solution of silicon according to the temperature of the metal. And forming a front electrode thereon.

Hereinafter, a configuration of a high efficiency solar cell according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective view illustrating a structure of a high efficiency solar cell according to an embodiment of the present invention, in which a recessed electrode structure solar cell is illustrated.

As shown in FIG. 1, a second conductive type, for example, an n-type semiconductor layer (hereinafter referred to as n-layer) having a conductivity type opposite to that of the first conductive type, for example, a p-type silicon substrate 11, is described below. 12 is formed, and a pn junction is formed at the interface between the p-type silicon substrate 11 and the n-layer 12 to show a pn structure which is an essential component of the solar cell.

SiO ₂ layers 13a and 13b are formed on the front surface of the n-layer 12 and the back surface of the p-type silicon substrate 11, respectively.

A plurality of grooves 14 are formed at a predetermined depth from which the silicon substrate 11 is exposed from the surface of the SiO ₂ layer 13a formed on the front surface of the n-layer 12. The n-type impurities are formed in the grooves 14. The highly doped n ⁺ silicon layer 15 is formed to a thickness of 1 to 5 μm, and a silicon-containing metal layer 16 containing a small amount of silicon is formed on the n ⁺ silicon layer 15 to form a groove 14. It is filling the inside.

At this time, the n ⁺ silicon layer 15 and the silicon-containing metal layer 16 is formed by the solution growth method using the difference in the solid solution of silicon according to the temperature of the metal, since the solution growth method is basically made in the thermal equilibrium state There is no thermal instability in the silicon substrate, and there are no defects in the n ⁺ silicon layer 15 and the silicon-containing metal layer 16 formed by the solution growth method.

The front electrode 17 is formed on the silicon containing metal layer 16.

On the back surface of the p-type silicon substrate 11, a back electrode pattern 18 is formed in which the SiO ₂ layer 13b is partially etched. The p-type silicon substrate 11 under the back electrode pattern 18 is locally formed. A p ⁺ region 19 doped with a high concentration of p-type impurities is formed, and a rear electrode 20 is formed on an upper front surface of the rear SiO ₂ layer 13b including the rear electrode pattern 18.

Then, a method of manufacturing a high efficiency solar cell according to an embodiment of the present invention as described above will be described in detail.

First, an n-layer 12 is formed by doping phosphorus (P) on the front surface of the p-type silicon substrate 11, and SiO is disposed on the front surface of the n-layer 12 and the back surface of the silicon substrate 11 for the antireflection effect. _Two layers 13a and 13b are formed.

Next, a plurality of grooves 14 are formed to a predetermined depth through which the silicon substrate 11 is exposed from the surface of the n layer 12 using chemical etching, mechanical scribing, laser, or the like.

Next, the silicon substrate structure in which the grooves 14 are formed is immersed in a metal molten metal saturated with silicon, and then the grooves 14 are formed by the solution growth method by lowering the temperature below the liquidus line of the corresponding composition in the state diagram of the metal and silicon. An n ⁺ silicon layer 15 heavily doped with metal and a silicon-containing metal layer 16 containing a small amount of silicon are formed therein.

At this time, metals used in the melt of the metal and silicon include Sb, Bi, As and the like. In addition, it is preferable that the silicon is saturated in the melt of the metal and silicon, and when the temperature of the melt is lowered, the cooling rate is preferably lowered to 2 ° C / min or less.

FIG. 2 is a phase diagram of the metal (M) and silicon, which includes a liquid phase region (L), a coexistence region (L + Si) of a liquid phase and a silicon solid phase, and a coexistence region (L + M) of a liquid phase and a metal solid phase. ), And the solid state region S is shown. As shown here, when the temperature of the metal melt (A) having a saturated composition of silicon is lowered by ΔT (B), the silicon becomes supersaturated by ΔX, and the supersaturated silicon is subjected to liquid epitaxy growth. Precipitates to solid through. In this case, the grown silicon layer contains 10 ¹⁹ / cm ³ or more of metal, and the silicon layer containing 10 ¹⁹ / cm ³ or more of the metal sufficiently performs the role of n ⁺ layer.

In addition, as described above, in the solution growth method, since the reaction proceeds in a direction for maintaining thermal equilibrium and the silicon layer grows, the n ⁺ silicon layer 15 is epitaxy only in the silicon substrate 11 exposed through the groove. It grows and does not grow in the SiO ₂ layer 13a.

As such, when the n ⁺ silicon layer 15 grows and the temperature falls below the eutectic point (denoted by E in FIG. 2), a solid phase having a composition of α: β of silicon and metal is precipitated, which is a silicon-containing metal layer. This corresponds to (16).

The amount of silicon present in the silicon-containing metal layer 16 is similar to the theoretical composition predicted from the state diagram, but there is a slight variation due to the difference in solubility of silicon in the metal. Therefore, the silicon content in the silicon containing metal layer 16 is 0.01 to 3 at%.

For example, when the metal is Bi, the silicon-containing metal layer 16 contains about 0.2 at% of silicon, and when the metal is As, about 1 at% of silicon is included.

Next, the front electrode 17 made of a material such as Ag, Cu, or the like is formed on the silicon-containing metal layer 16 by using a plating method, a vacuum deposition method, or a screen printing method.

Next, the SiO ₂ layer 13b formed on the back surface of the silicon substrate 11 is partially etched to form the back electrode pattern 18, and the silicon substrate 11 is doped with p-type impurities through the back electrode pattern 18. Next, a p ⁺ region 19 is formed locally, and then a back electrode 20 is formed on the upper front surface of the SiO ₂ layer 13b including the back electrode pattern 18, thereby completing solar cell manufacturing.

As described above, in the present invention, since the impurity is not formed when the n ⁺ silicon layer is formed by the melt growth method, and thus is formed as a defect-free layer, the impurity generated when heat treatment at a high temperature in order to form the n ⁺ region is performed. There is an effect that the inflow problem is solved, and also there is no heat load has the effect of improving the conversion efficiency of the solar cell.

In addition, since the process time is shortened compared to the conventional high temperature heat treatment, the energy cost is reduced.

In addition, when forming the front electrode on the n ⁺ silicon layer and the silicon-containing metal layer formed by the melt growth method according to the present invention, it is easy to apply low-cost processes such as plating and screen printing, resulting in a low-cost aspect There is an effect of realizing the manufacture of a battery.

Claims (7)

A first conductive semiconductor substrate; A second conductive semiconductor layer formed on the first conductive semiconductor substrate and having a conductivity type opposite to that of the first conductive semiconductor substrate; A pn junction formed at an interface between the first conductive semiconductor substrate and the second conductive semiconductor layer; An oxide film formed on the second conductive semiconductor layer; A plurality of grooves formed at a predetermined depth to expose the first conductive semiconductor substrate from an upper surface of the oxide film; An n ⁺ silicon layer formed to a predetermined thickness in the groove; A silicon-containing metal layer formed on the n ⁺ silicon layer and filling the inside of the groove; A front electrode formed on the silicon-containing metal layer; A rear electrode formed on the rear surface of the first conductive semiconductor substrate; A back oxide film formed on a rear surface of the first conductive semiconductor substrate; A back electrode pattern from which the back oxide film is partially removed; And A p ⁺ region locally formed in the first conductive semiconductor substrate under the back electrode pattern Including, The back electrode is formed on the upper front surface of the back oxide film including the back electrode pattern. The method of claim 1, The n ⁺ silicon layer is a solar cell formed to a thickness of 1 ~ 5 ㎛ with respect to the total depth of the groove. The method of claim 1, The n ⁺ silicon layer is a solar cell formed by a melt growth method using a melt of a metal and silicon forming silicon and silicide. The method of claim 3, wherein The n ⁺ silicon layer is a solar cell containing the metal 10 ¹⁹ / cm ³ or more. The method of claim 1, Solar cell containing 0.01 to 3 at% of silicon in the silicon-containing metal layer. delete A first conductive semiconductor substrate; A second conductive semiconductor layer formed on the first conductive semiconductor substrate and having a conductivity type opposite to that of the first conductive semiconductor substrate; A pn junction formed at an interface between the first conductive semiconductor substrate and the second conductive semiconductor layer; An oxide film formed on the second conductive semiconductor layer; A plurality of grooves formed at a predetermined depth to expose the first conductive semiconductor substrate from an upper surface of the oxide film; An n ⁺ silicon layer formed to a predetermined thickness in the groove; A silicon-containing metal layer formed on the n ⁺ silicon layer and filling the inside of the groove; A front electrode formed on the silicon-containing metal layer; And A rear electrode formed on the rear surface of the first conductive semiconductor substrate In the method of manufacturing a solar cell comprising: The n + silicon layer and the silicon-containing metal layer is formed by a solution growth method using a difference in the solid solution of silicon according to the temperature of the metal, Method for manufacturing a solar cell, characterized in that.

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