TWI455341B - Method for manufacturing solar cells - Google Patents

Description

Solar cell manufacturing method

The present invention relates to a method for producing a solar cell, and more particularly to a method for manufacturing a solar cell improved by a surface roughening by RIE technique.

It is known that in a solar cell structure, the illuminating surface generally has a concave-convex structure, thereby reducing the reflectance of the surface of the solar cell to light and increasing the incident ratio of sunlight. The surface uneven structure described above can be formed by etching the surface of the substrate by reactive ion etching (RIE).

Referring to FIG. 1, although the RIE process can etch the substrate 11 to meet the surface roughness of the substrate 11, the charged particles (plasma) in the process also react with the substrate 11 to form a plasma damage layer on the surface of the substrate 11. 12, the presence of the plasma destruction layer 12 will increase the recombination of the carrier, thereby reducing the photoelectric conversion efficiency of the solar cell, so after the RIE process, the plasma must be removed by wet etching. The destruction layer 12 is mainly composed of yttrium (Si) and lanthanum oxide (SiO _x ). Therefore, a solution such as potassium hydroxide (KOH) or hydrofluoric acid (HF) is usually used as the etching solution. After the destruction layer 12 is removed, a thermal diffusion process is subsequently performed to form a pn junction on the surface of the substrate 11.

However, the apparatus for performing wet etching is expensive, and another wet etching is necessary after the thermal diffusion process, that is, HF is used to remove SiO ₂ generated on the surface of the substrate 11 due to high temperature, so as described above. In the solar cell manufacturing equipment, two sets of wet etching equipment are required, resulting in high equipment and manufacturing cost, which is not conducive to industrial mass production.

Accordingly, it is an object of the present invention to provide a method of manufacturing a solar cell that reduces equipment costs and meets mass production requirements.

Therefore, the method for manufacturing a solar cell of the present invention comprises: (A) etching a first conductive type substrate by dry etching to have a surface having a high and low undulation, and a surface of the first conductive type substrate is further damaged by a plasma. (B) thermally diffusing the first conductive type substrate such that the first conductive type substrate forms a second conductive type doped layer under the plasma break layer, and the plasma damage layer is formed Oxidation and conversion into an oxide layer, the thermal diffusion process comprising a deposition phase and a drive-in phase, the drive-in phase being a drive-in time at a drive-in temperature of 800 ° C to 950 ° C The driving time is 20 minutes to 50 minutes; (C) removing the oxide layer by wet etching to complete the fabrication of the semi-finished product of the solar cell; and (D) forming an electrode on the semi-finished product of the solar cell.

When the driving temperature is too low and less than 800 ° C, the reaction gas molecules cannot generate sufficient moving kinetic energy due to insufficient temperature, so the diffusion effect is not good, which is disadvantageous for the formation of the second conductive type doped layer, and the electricity cannot be obtained. The slurry destruction layer is oxidized; when the driving temperature is too high and is greater than 950 ° C, the temperature resistance of the first conductive type substrate exceeds the temperature range, and warpage occurs. When the driving time is too short, the reaction gas molecules are not sufficiently diffused, which is not conducive to the formation of the second conductivity type. The doped layer, the plasma destruction layer can not be fully oxidized; the driving time can be up to 50 minutes to achieve the effect, and the additional time is only a waste of energy.

The effect of the present invention is that the plasma destruction layer is oxidized by improving the driving-in stage of the thermal diffusion treatment, and the oxide layer is removed by wet etching after the thermal diffusion treatment, so that the present invention can omit the wet etching before the thermal diffusion treatment. This can reduce equipment costs, facilitate mass production, and the solar cells produced still maintain a certain conversion efficiency.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention.

Referring to FIG. 2, a preferred embodiment of the manufacturing method of the present invention is used to fabricate a solar cell comprising a first conductive type substrate 2 and a second conductive type doped layer 4 stacked from bottom to top. An anti-reflection layer 5 and two electrodes 6 respectively located on the lower surface of the first conductive substrate 2 and the surface of the anti-reflection layer 5.

Referring to Figures 3 and 4, the method of manufacturing a solar cell of the present invention comprises:

(1) Step 71: The first conductive type substrate 2 is prepared. This embodiment is a p-type semiconductor germanium (Si) substrate, and is not limited thereto, and an n-type substrate may be used.

(2) performing step 72: etching a surface of the first conductive type substrate 2 by dry etching, in this embodiment, using reactive ion etching (Reactive Ion Etching, RIE for short), and using SF ₆ , Cl ₂ and O _{2 is} mixed as a reaction gas, and the surface of the first-conductivity-type substrate 2 is made to have a high and low undulation, that is, a rough texture in which irregularities are formed. Moreover, since the surface of the first conductive type substrate 2 reacts with the plasma, a plasma damage layer 3 is formed on the surface of the uneven rough microstructure, and the material of the plasma damage layer 3 is mainly tantalum and niobium. Oxide (SiO _x ).

(3) Performing step 73: performing thermal diffusion processing on the first conductive type substrate 2, the heat diffusion processing including a deposition stage and a drive-in stage. First, in the deposition stage, the first conductive substrate 2 is placed in a high temperature furnace tube, the temperature in the furnace tube is about 750 ° C ~ 800 ° C, and a reaction gas is introduced into the furnace tube, which is N _{2 in} this embodiment. -POCl ₃ (phosphorus oxychloride), a mixed gas of O ₂ and N ₂ , but is not limited thereto, and further deposits phosphorus (P) on the surface of the first conductive substrate 2 .

Then, the driving in phase is continued for a driving time at a driving temperature of 800 ° C to 950 ° C, preferably 810 ° C to 950 ° C, more preferably 850 ° C. ~900 ° C; the driving time is 20 minutes to 50 minutes, preferably 25 minutes to 37.5 minutes, so that the phosphorus (P) on the surface of the first conductive substrate 2 enters the surface layer of the first conductive substrate 2, Further, an n-type second conductive type doped layer 4 is formed under the plasma destruction layer 3, and the material thereof is mainly phosphorus glass (PSG); this step is also equivalent to being close to the surface in the first conductive type substrate 2 ( The surface means that the second conductive type doped layer 4 is formed at the surface etched by the dry etching method of step 72.

Moreover, in the driving-in stage, the reactive gas molecules also diffuse into the plasma destruction layer 3, and are oxidized to become an oxide layer 3' due to a higher temperature and time setting, and the oxide layer 3' material Mainly oxides of cerium oxide, phosphorus and cerium; the oxide layer 3' is equivalent to being formed on the first conductive type The side of the board 2 is adjacent to the surface (the surface refers to the surface etched by the dry etching of step 72).

In addition, when the n-type semiconductor is used for the first conductive type substrate 2, the second conductive type doped layer 4 formed by thermal diffusion treatment is a p-type semiconductor.

(4) Step 74 is performed: the oxide layer 3' is removed by wet etching to expose the second conductivity type doping layer 4. This embodiment uses a solution such as hydrofluoric acid (HF) as an etching solution.

(5) Step 75 is performed to form an anti-reflection layer 5 of tantalum nitride on the surface of the second conductive type doped layer 4, and the anti-reflection layer 5 can reduce the reflection of sunlight and increase the incident ratio of light. In practice, it can be carried out by techniques such as sputtering or plasma assisted chemical vapor deposition (PECVD).

At this time, the semi-finished product of the solar cell has been completed, but it should be noted that the formation of the anti-reflection layer 5 is not an essential step, and therefore the anti-reflection layer 5 may not be included in the semi-finished product of the solar cell.

(6) Step 76: An electrode 6 is formed on the semi-finished product of the solar cell, and the electrode 6 is formed on the upper surface of the anti-reflection layer 5 and the lower surface of the first conductive substrate 2 mainly by screen printing. The shape of the electrode 6 in FIG. 3 is merely illustrative and not limiting, and may be in other designs.

(7) Performing step 77: placing the sample subjected to step 76 in a high temperature sintering furnace, wherein the sintering furnace has a plurality of high temperature regions having different temperatures, and the rollers in the furnace drive the sample to continue to advance and are sintered at different high temperatures, the electrodes 6 Therefore, it can be firmly attached, thus completing the fabrication of the solar cell.

Compared with the prior art process, the present invention mainly omits the wet etching before the thermal diffusion treatment, and improves the driving stage of the thermal diffusion treatment by driving The combination of the temperature and the driving time can also oxidize the plasma destruction layer 3 when the second conductive type doping layer 4 is formed. The advantage is that in the existing solar cell process, after the thermal diffusion treatment, the original Wet etching is necessary, and because the hydrofluoric acid solution has a good etching effect on the oxide, the present invention directly removes the oxide layer 3' by using the wet etching step, and the oxide layer 3' is oxidized by the plasma. Destruction of the layer 3, so that the thickness of the oxide layer 3' is in principle thicker relative to the plasma destruction layer 3, it is easier to control to completely etch it, and to avoid damage to the second conductivity type doping layer 4.

Referring to Table 1, the following experimental examples demonstrate that the solar cell produced by the present invention still has good performance. Table 1 V _oc represents the open circuit voltage, J _sc represents the short circuit current, FF value represents the fill factor, and Eff. is the conversion efficiency. In the range of the driving temperature and the driving time defined in Experimental Examples 1 to 8, the short-circuit current, the FF value, and the conversion efficiency of each sample can reach a certain standard. In contrast, in Comparative Example 1, the driving temperature is 780 ° C and lower than 800 ° C, the moving kinetic energy of the reaction gas molecules is insufficient, and the diffusion effect is not good, which is disadvantageous for the formation of the second conductive type doped layer 4, and the plasma destruction layer 3 thereof Also, it was not sufficiently oxidized and completely removed, resulting in poor short-circuit current and conversion efficiency of Comparative Example 1.

In summary, the present invention improves the driving-in stage in the thermal diffusion process, and omits the wet etching of the conventional method before the thermal diffusion process. Therefore, only one set of wet etching equipment is required in the process of the present invention, thereby reducing equipment cost, It is advantageous for mass production, and the produced solar cells still maintain a certain conversion efficiency. Therefore, the present invention takes into consideration the feasibility of mass production and the quality of solar cells.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

2‧‧‧First Conductive Substrate

3‧‧‧plasma damage layer

3'‧‧‧Oxide

4‧‧‧Second conductive doped layer

5‧‧‧Anti-reflective layer

6‧‧‧Electrode

71~77‧‧‧Steps

1 is a schematic view of a known solar cell; FIG. 2 is a schematic view showing a solar cell manufactured by a preferred embodiment of the method for fabricating a solar cell of the present invention; and FIG. 3 is a schematic view showing the steps of the preferred embodiment. And Figure 4 is a flow chart of the steps of the preferred embodiment.

71~77‧‧‧Steps

Claims (8)

A method for manufacturing a solar cell, comprising: providing a first conductive type substrate; etching a surface of the first conductive type substrate by dry etching; and forming a second conductive type near the surface in the first conductive type substrate a doped layer, an oxide layer is formed on the first conductive type substrate near the surface side; the oxide layer is removed by wet etching; and an electrode is formed on the first conductive type substrate. The method for manufacturing a solar cell according to claim 1, wherein the first conductive type substrate is subjected to a thermal diffusion treatment to form the second conductive type doped layer, and the heat diffusion treatment is driven at a temperature of 800 ° C ~ 950 ° C. The method for producing a solar cell according to claim 2, wherein the heat diffusion treatment has a driving time of 20 minutes to 50 minutes. The method for producing a solar cell according to claim 2, wherein the heat diffusion treatment has a driving time of 25 minutes to 37.5 minutes. The method for producing a solar cell according to claim 1, wherein the dry etching method is a reactive ion etching method. The method for producing a solar cell according to claim 1, wherein the etching solution of the wet etching method is a hydrofluoric acid solution. Method for manufacturing solar cell according to item 1 of the patent application scope And forming an anti-reflection layer on the second conductive type doped layer after removing the oxide layer and forming the electrode. The method of manufacturing a solar cell according to claim 7, further comprising a sintering step for forming the electrode.