KR20130036127A - Method for forming elctrode of hetero-junction with intrinsic thin layer solar cell device - Google Patents

Abstract

PURPOSE: A method for forming a heterojunction solar cell is provided to reduce an electrode area by selectively depositing copper with a low resistance. CONSTITUTION: The front and the rear of an n-type Si layer are textured. An intrinsic amorphous Si layer(110) is formed on the front or the rear of the n-type Si layer. A p-type amorphous Si layer is formed on the front or the rear of the intrinsic amorphous Si layer. A TCO layer(140) is formed on the front or the rear of the p-type amorphous Si layer. A seed layer(150) is formed on the front and the rear of the p-type amorphous Si layer. Copper is formed by a simultaneous deposition method and a cap is deposited. An annealing process and an edge isolation process are performed.

Description

Electrode formation method of heterojunction solar cell {METHOD FOR FORMING ELCTRODE OF HETERO-JUNCTION WITH INTRINSIC THIN LAYER SOLAR CELL DEVICE}

Electrode deposition process technology for solar cell electrode formation

The present invention relates to a method for forming electrode wiring of a heterojunction solar cell, and more particularly, to a high efficiency that can be completely embedded in a metal layer without a separate firing process of the electrode using a conventional Ag paste using an electroless deposition process technology And a method for forming an ultra low cost metal electrode. The metal electrode of the heterojunction silicon solar cell is currently using the screen printing method using silver paste. However, the screen printing method using silver paste in the field of silicon solar cells, which has a great influence on the efficiency and cost of the entire cell, can be pointed out as one of the major disadvantages in the high efficiency of silicon solar cells. In addition, electrode design and electrode formation process must be very sensitive to electrode materials and electrode material deposition methods, and these electrode materials and formation methods need to be optimized for low cost and high efficiency. It is important to select the proper electrode material and proper formation technique. The screen printing technique widely used in commercially available solar cells has the advantages of relatively low cost of materials and unit processing equipment, large quantities of products can be produced in a large area in a short time in the air, and suitable electrode materials can be selectively applied. have. However, as raw material prices of silver, the main material, have soared every year, they face serious problems in terms of economic efficiency, and the electrode material itself contains glass frit components, which has the disadvantage that the specific resistance is very high. It is pointed out as a factor. In addition, the Ag front electrode formed by screen printing on the front side of the emitter may have a large electrode resistance due to the phenomenon of diffusion penetration into the substrate starting from the junction surface of the electrode and the emitter surface during the heat treatment process, resulting in electrode efficiency. The decline is inevitable. In addition, as the thickness of the silicon solar cell becomes thinner, the defect rate at which the substrate is broken due to the pressure during the silver screen printing is also increasing. Therefore, a new electrode formation method is needed to overcome this problem. During printing and firing at high temperatures, wafers become thinner, resulting in high defect rate.The resistance of glass frit in Ag electrode increases, which is a barrier to high efficiency. Above all, the cost of Ag raw materials is rising rapidly. To reduce, there is an urgent need for new materials, processes, and equipment technologies to replace Ag.

A HIT (Hetero-junction with Intrinsic Thin layer) structured solar cell using the advantages of amorphous silicon and single crystal silicon was developed at Sanyo Electric Co., Ltd. in Japan. Unlike conventional solar cells, where emitters are formed by high temperature diffusion, HIT structures feature p-type and intrinsic amorphous silicon to form crystalline silicon. The amorphous layer only forms a junction and the area that actually absorbs light is the crystalline silicon beneath it. In addition, by providing an insulating layer on the junction interface, the desaturation density of the battery is reduced, which is excellent in temperature characteristics compared to general solar cells. It is also a big advantage that the entire process is carried out at low temperature since the amorphous thin film is usually possible under 400 ° C. However, since the front amorphous has low conductivity, a transparent conductive film should be used as an auxiliary electrode. However, reflection or absorption in the transparent conductive film reduces the conversion efficiency. Using intrinsic layers, the change efficiency at the lab level is 23%.

The difference between the structure of conventional crystalline silicon solar cells and HIT solar cells is the formation of emitters. It is divided into whether the emitter is formed by homogeneous junction or heterojunction. In the case of homogeneous bonding, a high temperature heat treatment process is essential by forming doping on the wafer surface. In addition, a high temperature heat treatment process is required to form a backside electric field. On the other hand, in the case of the HIT cell, the a-Si: H thin film is used to form an emitter on the front side and an electric field on the back side, which does not go through such a high temperature heat treatment process. The present invention relates to a novel electrode formation method and a laminated structure thereof applied to such heterojunction silicon solar cells.

In the method of forming the electrode wiring of the heterojunction solar cell using the selective deposition characteristic, in the method of forming the metal electrode wiring in the heterojunction solar cell device using the selective deposition method, the texturing is formed on the front and back surfaces of the n-type Si. Forming an intrinsic amorphous-Si on the front or back, followed by forming a p-type amorphous-Si on the front or back, followed by forming a TCO layer on the front or back Next, forming a seed layer on the front and rear surfaces, followed by forming a Cu layer on the front and back surfaces by a simultaneous deposition method, followed by a deposition process including a cap deposition step, is followed by annealing. And a method of performing a method of processing an edge isolation process afterwards.

In order to improve efficiency with a selective electroless process by replacing the conventional process using silver paste.

The difference between the structure of conventional crystalline silicon solar cells and HIT solar cells is the formation of emitters. It is divided into whether the emitter is formed by homogeneous junction or heterojunction. In the case of homogeneous bonding, a high temperature heat treatment process is essential by forming doping on the wafer surface. In addition, a high temperature heat treatment process is required to form a backside electric field. On the other hand, in the case of the HIT cell, the a-Si: H thin film is used to form an emitter on the front side and an electric field on the back side, which does not go through such a high temperature heat treatment process. The present invention relates to a novel electrode formation method and a laminated structure thereof applied to such heterojunction silicon solar cells.

According to the solar cell electrode wiring forming method of the present invention, a metal plating layer can be formed by performing an electroless plating method without a separate firing process, and alternative Ag Screen Printing electrode forming technology of raw materials is a selective electrode forming Ni-Cu process. It is possible to improve efficiency by reducing resistance and reducing electrode area when replacing, and above all, it is possible to reduce electrode formation cost by more than 50%.

According to the present invention, after forming the metal electrode forming portion of the arc layer, a separate photoresist forming process is required by selectively depositing only the metal electrode forming portion by controlling the formation of a nickel or copper layer on the arc layer using an electroless plating method. The present invention relates to a process for forming a new electrode wiring, which can be performed without any copper, and selectively deposits low-resistance copper, thereby improving efficiency by reducing electrode area of a solar cell and improving efficiency due to low resistance. Therefore, the present invention can solve the problems of the prior art of the conventional silver screen printing method and improve the performance of the solar cell through low cost, high efficiency.

1A to 1H are cross-sectional views illustrating a metal wiring forming method of a heterojunction solar cell device according to the present invention.
1A: Form N or P Type on Silicon Substrate
Figure 1b: deposit an intrinsic amorphous layer
1C and 1D: forming p-type amorphous-Si on the front or back side
Figure 1e: forming a transparence conducting oxide (TCO) on the front, back
1f: seed layer forming step
Figure 1f: Electroless / Electrolytic Capping Step

EMBODIMENT OF THE INVENTION Preferred embodiment of this invention is described in detail with reference to an accompanying drawing. 1H is a cross-sectional view showing a metal electrode wiring formation method of a heterojunction solar cell according to the present invention.

Referring to FIGS. 1A and 1B, a P-type or N-type is formed on the silicon substrate 100 of FIG. 1A, and text etching may be performed by wet etching including wet etching or plasma etch. Dry etch) process. Subsequently, an intrinsic amorphous layer is deposited as shown in FIG. 1B.

As shown in FIGS. 1C and 1D, as a step of forming a p-type amorphous-Si on the front surface or the rear surface, (120), (130) physical vapor deposition or chemical vapor deposition is possible, and SiON, Si3N4, and SiOx films are formed. The method can also be applied.

Next, FIG. 1E illustrates a method of depositing TCO such as indium tin oxide (ITO) and ZnO (Al) as a transparent conductive oxide in forming a transparence conducting oxide (TCO) on the front and back surfaces.

As shown in FIG. 1F, a method of forming the seed layer is possible.

As a step of forming the seed layer, a method of forming a seed layer applying Ag paste may be used as the seed layer, and a method including a material and a process of applying Ag as another seed layer may be possible. In addition, the seed layer includes a material and a process for applying Cu, and the sputtering method is possible for the Cu deposition method. A solar cell electrode formation method is possible. In addition, the seed layer includes materials and processes that apply Sn, materials and processes that apply Ni, materials and processes that apply Mo (molybdenum), materials and processes that apply Co, W, and such seed layers. Examples of deposition methods for materials applied to these fields include sputtering method, CVD method, evaporation method, ALD method, heterojunction solar cell electrode formation method that can be applied by electroless / electrolytic plating method, and other electrode parts for forming such electrodes. Selective electroless plating is performed as a method for forming an electrode after applying the method of removing the seed layer. In the selective electrode deposition process including the selective copper (Cu) deposition, selective cap deposition step, in the selective copper (Cu) deposition method, the deposition solution comprises Cu, NaOH, HCHO, EDTA, H2O components and the composition thereof is Copper (Cu) has a range of 0.5-10 g / L, NaOH has a range of 1-20 g / L, HCHO has a range of 0.1-3%, and EDTA has a range of 0.1-2%. Have The treatment temperature for selective copper (Cu) deposition ranges from -10C to 90C and the treatment time ranges from 1sec to 60min. Deposition time has a temperature range of 1sec ~ 10min. The deposition thickness of the selective copper (Cu) layer includes a deposition process in the range of about 500 A ~ 30um. Selective copper deposition is deposited by repeating the deposition cycle in the range of 20sec ~ 10min 1 ~ 6 times after DI treatment in 20sec ~ 10min range. Figure 1g shows this process step. After selective copper (Cu) deposition, the subsequent cleaning process should proceed without time delay. If there is a time delay, cleaning is performed after selective copper (Cu) deposition. Selective copper (Cu) deposition after the cleaning (Cleaning) process to proceed the heat treatment is possible. The heat treatment is performed at room temperature-600 C for 1 minute-3 hours. At this time, the hydrogen reduction atmosphere includes the case of applying only H2 and using a hydrogen mixture gas such as H2 + Ar (1-95%), H2 + N2 (1-95%), and performing heat treatment in the Ar atmosphere or N2. It is also possible to heat-treat in an atmosphere. Heat treatment process is to proceed in-situ process, nickel (Ni) after deposition (Cleaning) process proceeds in 1sec ~ 5min after proceeding.

 This heat treatment process can be omitted depending on the conditions of the subsequent process.

In the selective deposition process including selective copper (Cu) deposition and selective cap deposition after seed layer electrode formation, the selective cap deposition method may include Ag, Sn, Ag-Sn, Pb, Co, W, Ni etc. vapor deposition is possible. In a selective deposition process including a selective cap deposition step, in the method of selective nickel (Ni) deposition, the deposition solution includes Ni, H ₂ PO ₂ , NH 4 OH, NH 4 Cl, and H ₂ O components, and the composition thereof is nickel (Ni). Has a range of 0.01-10 g / L, H ₂ PO ₂ has a range of 0.5-8%, NH 4 OH has a range of 0.1-5%, and NH 4 Cl has a range of 0.1-5%. The treatment temperature for selective nickel (Ni) deposition ranges from -30C to 80C and the treatment time ranges from 1sec to 10min. Deposition time has a temperature range of 1sec ~ 10min. The thickness of the selective nickel (Ni) layer includes a process in which the deposition thickness is in the range of 50 A to 3 μm in order to increase the stability of the diffusion barrier layer to prevent the minimum decrease of resistance and copper (Cu) diffusion. Figure 1h shows the structural diagram of the final heterojunction solar cell completed through this cap process.

100: silicon substrate
110: intrinsic a-Si Layer
120: front p-type a-Si Layer
130: rear p-type a-Si layer
140: transparent conductive oxide (TCO) layer layer
150: seed formation and seed patterning step
160: optional electroless copper deposition step
170: electroless / electrolytic capping step

Claims (17)

A method of forming a metal electrode wiring in a solar cell device using an electroless / electrolytic plating method as a method of forming an electrode of a silicon heterojunction solar cell, comprising the steps of: forming texturing on the front and rear surfaces of n-type Si; Forming an intrinsic amorphous-Si on the front or back, followed by forming a p-type amorphous-Si on the front or back, followed by forming a TCO layer on the front or back Forming a seed layer on the front rear surface, followed by forming a Cu layer on the front and back surfaces by a simultaneous deposition method, and then applying a deposition process including a cap deposition step, and then annealing the process. Afterwards, the metal isolation of the silicon heterojunction solar cell applying the electroless / electrolytic deposition process as a method of processing the edge isolation process. Invention to form a wiring. The method of claim 1,
In the step of forming the transparence conducting oxide (TCO) on the front and back, the transparent conductive oxide includes all kinds of TCO such as indium tin oxide (ITO) and ZnO (Al). Forming the seed layer as a seed layer includes a material and a process for applying Ag paste. The method of claim 1,
The seed layer is a step of forming a seed layer, which includes a material and a process of applying Ag, and the deposition of Ag is possible by applying a sputtering method, a CVD method, an evaporation method, an ALD method, and an electroless / electrolytic plating method. Heterojunction solar cell electrode formation method. The method of claim 1,
Forming a seed layer, the seed layer includes a material and a process for applying Cu, and Cu deposition is possible by sputtering method, CVD method, evaporation method, ALD method, electroless / electrolytic plating method. Heterojunction solar cell electrode formation method. The method of claim 1,
Forming a seed layer, the seed layer includes a material and a process of applying Sn, and the deposition of Sn by sputtering, CVD, evaporation, ALD, and electroless / electrolytic plating methods is possible. Heterojunction solar cell electrode formation method. The method of claim 1,
Forming a seed layer, the seed layer includes a material and a process for applying Ni. Ni deposition is possible by sputtering, CVD, evaporation, ALD, and electroless / electrolytic plating. Heterojunction solar cell electrode formation method. The method of claim 1,
Forming a seed layer includes a material and a process for applying Mo (molybdenum) as a seed layer, and the deposition method of Mo (molybdenum) by sputtering method, CVD method, evaporation method, ALD method, electroless A method for forming a heterojunction solar cell electrode capable of depositing by electrolytic / electrolytic plating. The method of claim 1,
Forming a seed layer includes a material and a process for applying Co and W as a seed layer, and sputtering method, CVD method, evaporation method, ALD method, and electroless / electrolytic plating method are used for the deposition method of Co and W. Heterogeneous solar cell electrode formation method that can be applied deposition. The method of claim 1,
Heterojunction solar cell electrode formation method applying a method of removing the seed layer other than the electrode portion for forming the electrode. The method of claim 1,
In the selective electrode deposition process including the selective copper (Cu) deposition, selective cap deposition step, in the selective copper (Cu) deposition method, the deposition solution comprises Cu, NaOH, HCHO, EDTA, H2O components and the composition thereof is Copper (Cu) has a range of 0.5-10 g / L, NaOH has a range of 1-20 g / L, HCHO has a range of 0.1-3%, and EDTA has a range of 0.1-2%. Have 12. The method of claim 11,
The treatment temperature for selective copper (Cu) deposition ranges from -10C to 90C and the treatment time ranges from 1sec to 60min. Deposition time has a temperature range of 1sec ~ 10min. The deposition thickness of the selective copper (Cu) layer includes a deposition process in the range of about 500 A ~ 30um. Selective copper deposition is deposited by repeating the deposition cycle in the range of 20sec ~ 10min 1 ~ 6 times after DI treatment in 20sec ~ 10min range. 12. The method of claim 11,
After selective copper (Cu) deposition, the subsequent cleaning process should proceed without time delay. If there is a time delay, cleaning is performed after selective copper (Cu) deposition.




The method of claim 11, wherein a method of performing a heat treatment after a selective copper (Cu) deposition followed by a cleaning treatment is performed. The heat treatment method is performed at a temperature of 600 ° C. for 1 minute to 3 hours. At this time, the hydrogen reduction atmosphere includes the case where only H2 is applied and the hydrogen mixture gas such as H2 + Ar (1-95%), H2 + N2 (1-95%), etc., and the heat treatment in the Ar atmosphere or the N2 atmosphere Heat treatment at is also possible.
Heat treatment process is to proceed in-situ process, nickel (Ni) after deposition (Cleaning) process proceeds in 1sec ~ 5min after proceeding. This heat treatment process can be omitted depending on the conditions of the subsequent process.
The method of claim 1,
In the selective deposition process including selective copper (Cu) deposition and selective cap deposition after seed layer electrode formation, the selective cap deposition method may include Ag, Sn, Ag-Sn, Pb, Co, W, Ni etc. vapor deposition is possible. The method of claim 1,
In a selective deposition process including a selective cap deposition step, in the method of selective nickel (Ni) deposition, the deposition solution includes Ni, H ₂ PO ₂ , NH 4 OH, NH 4 Cl, and H ₂ O components, and the composition thereof is nickel (Ni). Has a range of 0.01-10 g / L, H ₂ PO ₂ has a range of 0.5-8%, NH 4 OH has a range of 0.1-5%, and NH 4 Cl has a range of 0.1-5%.
17. The method of claim 16,
The treatment temperature for selective nickel (Ni) deposition ranges from -30C to 80C and the treatment time ranges from 1sec to 10min. Deposition time has a temperature range of 1sec ~ 10min. The thickness of the selective nickel (Ni) layer includes a process in which the deposition thickness is in the range of 50 A to 3 μm in order to increase the stability of the diffusion barrier layer to prevent the minimum decrease of resistance and copper (Cu) diffusion.

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