TW201336093A - Solar cell and its manufacturing method - Google Patents

Abstract

A solar cell and its manufacturing method, wherein the mentioned cell comprises: a photoelectric conversion unit, a dielectric layer, a few back-surface field structures, and a first and a second conductive glue layers containing the glass material. The second conductive glue layer is covered onto the dielectric layer, and its glass content ration is smaller than that of the first conductive glue layer. By means of two different materials to make the first and second conductive layers to be used as the back-surface electrode of the cell and adjusting the glass content in the material according to the disposition position and function of the mentioned conductive glue layer, the two materials are made to have different erosion capabilities, therefore on one hand capable of forming the back surface filed structure with high thickness and excellent quality, and on the other hand capable of maintaining the quality and function of the dielectric layer to enhance the characteristics of the open-circuit voltage and the conversion efficiency of the cell.

Description

Solar cell and method of manufacturing same

The present invention relates to a solar cell and a method of fabricating the same, and more particularly to a twinned solar cell and a method of fabricating the same.

Referring to FIG. 1 , it is a schematic diagram of a manufacturing process of a known solar cell 1 . The structure of the solar cell 1 is described first (please refer to the last process of FIG. 1 ), which mainly includes: a wafer 11 , a dielectric layer 12 , A plurality of local back surface fields (LBSF) 13 formed at a partial portion of the wafer 11, and a back electrode 14.

The wafer 11 is used for converting light energy into electrical energy, and includes a p-type germanium substrate, an n-type emitter layer formed on the substrate, and a film layer such as an anti-reflection film. The dielectric layer 12 is formed on a back surface 111 of the wafer 11 for reducing the rate of carrier recombination on the surface of the wafer 11, thereby improving the efficiency of the battery. The dielectric layer 12 has a plurality of through-holes 121. The back electric field structure 13 is formed on the back surface 111 corresponding to the through hole 121. The back electric field structure 13 is a p-type semiconductor material, and the carrier concentration is larger than the p-type germanium substrate, and the electric field is used to block electrons toward the back surface 111. The direction of movement causes electrons to be collected on the n-type emitter layer of the wafer 11 to improve conversion efficiency. The back electrode 14 is located on the surface of the dielectric layer 12 and partially extends into the through hole 121 of the dielectric layer 12 to form an electrical connection with the back surface 111 of the wafer 11, and transmits the power generated by the wafer 11 through the back electrode 14. To the outside.

The solar cell 1 is formed by first forming a complete dielectric layer 12 on the back surface 111 of the wafer 11, and removing the local etching of the dielectric layer 12 to form the through hole 121, and then using the screen printing method. An aluminum paste is coated on the surface of the dielectric layer 12, and then the wafer 11 is sintered. The aluminum paste material is dried to form the back electrode 14, and the aluminum paste material is diffused into the wafer 11, so that the wafer 11 is partially formed. A back electric field structure 13 composed of an aluminum-niobium mixed material.

Since the content of the glass frit in the aluminum paste affects the erosion ability of the aluminum paste, under certain limits, when the erosion ability of the aluminum paste is stronger, the mixing effect of the aluminum and the crucible in the substrate is better. The thicker the back electric field structure 13 formed by sintering, the better the quality. However, since the aluminum paste material also erodes the dielectric layer 12 to cause damage, thereby affecting the quality and function of the dielectric layer 12, the corrosion property of the aluminum paste material cannot be considered in consideration of the quality of the dielectric layer 12. If it is too high, the thickness of the back electric field structure 13 is insufficient, thereby affecting characteristics such as open circuit voltage and conversion efficiency of the battery.

Accordingly, an object of the present invention is to provide a solar cell capable of improving characteristics such as an open circuit voltage and a conversion efficiency, and a method of manufacturing the same.

Thus, the solar cell of the present invention comprises: a photoelectric conversion unit, a dielectric layer, a plurality of back electric field structures, a first conductive adhesive layer containing a glass material, and a second conductive adhesive layer containing a glass material.

The photoelectric conversion unit is configured to convert light energy into electrical energy, and includes an opposite light incident surface and a back surface. The dielectric layer is disposed adjacent to the back side and includes a plurality of perforations. The back electric field structures are respectively located at the back surface of the photoelectric conversion unit corresponding to the perforations. The first conductive paste layer includes a plurality of conductive contacts respectively located in the through holes and contacting the back electric field structure. The second conductive adhesive layer is coated on the dielectric layer, and the glass content ratio of the second conductive adhesive layer is smaller than the glass content ratio of the first conductive adhesive layer.

The method for manufacturing a solar cell of the invention comprises:

Step A: forming a dielectric layer having a plurality of perforations on a back surface of a photoelectric conversion unit;

Step B: coating a first slurry on the dielectric layer and corresponding to the portion of the perforation;

Step C: coating a second slurry on the dielectric layer and the first slurry, and a glass content ratio of the second slurry is smaller than a glass content ratio of the first slurry;

Step D: performing sintering to form the first slurry to form a first conductive adhesive layer, the second paste forming a second conductive adhesive layer, and forming a plurality of corresponding perforations corresponding to the photoelectric conversion unit The back electric field structure at the back.

The effect of the invention is that the back electrode of the battery is formed by two materials, and the glass content in the material is adjusted according to the position and function of the first conductive adhesive layer and the second conductive adhesive layer, so that the two materials are different. The erosion ability, on the one hand, can form a thick electric field structure with good thickness and good quality, on the other hand, it can maintain the quality and function of the dielectric layer, thereby improving the open circuit voltage and conversion efficiency of the battery.

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.

Referring to FIG. 2, a preferred embodiment of the solar cell of the present invention comprises: a photoelectric conversion unit 2, a dielectric layer 3, a plurality of back electric field structures 4, a first conductive adhesive layer 5, and a second conductive adhesive layer 6. .

The photoelectric conversion unit 2 is configured to convert light energy into electrical energy, and includes a light incident surface 21 and a back surface 22 opposite to the light incident surface 21. The photoelectric conversion unit 2 actually includes a substrate having the back surface 22, an emitter layer formed on the substrate, and a film layer such as an anti-reflection film. Wherein, the emitter layer is a semiconductor material, and the conductive form of the main carrier is not limited as long as the emitter layer can form a p-n junction with the substrate. In the present embodiment, the substrate is a p-type germanium substrate, and the emitter layer is an n-type emitter layer, but is not limited thereto.

The material of the anti-reflection layer, such as tantalum nitride (SiN _x ), is used to reduce the reflection of sunlight, increase the incidence of light, and reduce the surface recombination velocity (SRV), but the photoelectric conversion unit 2 It is not necessary to provide the anti-reflection layer. Since the structural design of the photoelectric conversion unit 2 is not a modification of the present invention, it will not be described in detail, and the figure is only illustrated by a single layer. It should be noted that the present invention does not necessarily limit the specific structure and the number of layers of the photoelectric conversion unit 2, because a film layer of different functions can be added depending on the demand of the solar cell.

In addition, a front surface electrode (not shown) is further disposed on the battery, and the bottom of the front electrode can be electrically connected to the emitter layer through the anti-reflection layer, the front electrode and the first conductive adhesive layer 5, The second conductive paste layer 6 cooperates to transfer the electric energy generated by the photoelectric conversion unit 2 to the outside, but since the front electrode is not an improvement point of the present invention, it will not be described.

The dielectric layer 3 is also generally referred to as a passivation layer adjacent to the back surface 22 of the photoelectric conversion unit 2 and includes a first face 31 facing the back face 22 and a second face opposite the first face 31. a surface 32, and a plurality of through holes 33 extending through the first surface 31 and the second surface 32. The material of the dielectric layer 3 is an oxide, a nitride, or a composite of an oxide and a nitride, specifically, for example, SiO. _x , SiN _x , Al ₂ O ₃ , or a composite layer such as SiO ₂ /SiN _x , Al ₂ O ₃ /SiN _x ... and the like. The dielectric layer 3 is used to fill and reduce surface defects, thereby reducing the recombination rate of the carrier at the back surface 22 of the photoelectric conversion unit 2, and improving the conversion efficiency of the battery.

The back electric field structure 4 is located at the back surface 22 of the photoelectric conversion unit 2 corresponding to the through hole 33, and the back electric field structure 4 of the embodiment is a p-type semiconductor formed by an aluminum-bismuth (Al-Si) mixed material. The carrier concentration is greater than the carrier concentration of the p-type germanium substrate, and the electric field of the back electric field structure 4 blocks the electrons from moving toward the back surface 22, so that electrons are collected in the n-type emitter of the photoelectric conversion unit 2. Polar layer to improve carrier collection efficiency and conversion efficiency.

The first conductive adhesive layer 5 is formed by screen printing a paste-like metal paste and drying and solidifying after firing. The metal paste used in the embodiment is an aluminum paste, and the main component thereof is aluminum, wherein Contains a small amount of glass frit and other ingredients. The first conductive adhesive layer 5 includes a plurality of conductive contacts 51 respectively located in the through holes 33 of the dielectric layer 3 and contacting the back electric field structure 4, and a plurality of respective conductive contacts 51 protruding from the through holes. The conductive protrusions 52 are spaced apart from each other and are spaced apart from each other, and the conductive protrusions 52 are in contact with a partial surface of the second face 32 of the dielectric layer 3.

The second conductive adhesive layer 6 of the present embodiment is coated on the second surface 32 of the dielectric layer 3 and the conductive protrusions 52 of the first conductive adhesive layer 5. The second conductive adhesive layer 6 is also formed by screen printing a paste-like metal paste and drying and solidifying after sintering. The metal paste of the embodiment is an aluminum paste, and the main component thereof is aluminum, and a small amount thereof is also contained therein. Glass frit and other ingredients. The second conductive adhesive layer 6 is an aluminum conductive adhesive layer, and the glass content ratio thereof must be smaller than the glass content ratio of the first conductive adhesive layer 5, the reason of which will be described later. The second conductive adhesive layer 6 is combined with the first conductive adhesive layer 5 as a back electrode of the battery.

It is worth mentioning that the second conductive adhesive layer 6 of the present invention is formed by screen printing using a metal paste without using a vacuum-coated film form because the germanium substrate of the general battery is thinner and more fragile, and the metal paste is used. The layer formed by the material has a certain supporting force compared with the film, so that the second conductive adhesive layer 6 made of a metal paste can be used to increase the strength of the substrate, and the second formed after high-temperature sintering. The thickness of the conductive paste layer 6 is preferably 20 μm to 30 μm to provide sufficient strength. In addition, the glass material in the metal paste can enhance the adhesion between the dielectric layer 3 and the second conductive adhesive layer 3 to be adhered to the dielectric layer 3.

Referring to Figures 2, 3 and 4, a preferred embodiment of the method of fabricating a solar cell of the present invention comprises:

(1) Step 71: First, the photoelectric conversion unit 2 is formed, including a step of forming a pn junction on the substrate by a diffusion process, forming an anti-reflection film, and the like, and then forming the dielectric on the back surface 22 of the photoelectric conversion unit 2 Layer 3, and the perforations 33 are formed on the dielectric layer 3. Since the method of manufacturing the photoelectric conversion unit 2 and the dielectric layer 3 is not an improvement of the present invention, it will not be described.

(2) performing step 72: applying a first paste 5' on the dielectric layer 3 and corresponding to the through hole 33 by screen printing, the first paste 5' being filled in the In the through hole 33, and on a partial surface of the dielectric layer 3, the first paste 5' is a slurry for forming the first conductive paste layer 5. The first slurry 5' is then dried and shaped through a baking step to facilitate subsequent processing.

(3) performing step 73: coating a second paste 6' on the dielectric layer 3 and the first paste 5' by screen printing, and the second paste 6' is used to form the A slurry of the second conductive paste layer 6.

The second slurry 6' and the first slurry 5' of this embodiment are both aluminum pastes. As described above, the main component of the aluminum paste is aluminum, and also contains a small amount of glass material and other components. Preferably, the first slurry 5' may comprise from 2 wt% to 7 wt% of glass material, and the second paste 6' may comprise from 1 wt% to 5 wt% of glass material. Further, the glass content ratio of the second slurry 6' must be smaller than the glass content ratio of the first slurry 5'.

(4) performing step 74: performing high temperature sintering to dry and solidify the first slurry 5' to form the first conductive adhesive layer 5, and the second paste 6' is dried and solidified to form the second conductive adhesive layer 6 And during the sintering process, the aluminum paste material of the first paste 5' is diffused from the position of the through hole 33 of the dielectric layer 3 to the back surface 22 of the photoelectric conversion unit 22, and the metal aluminum is thus doped to the photoelectric conversion. The ruthenium substrate of the unit 2 is combined with ruthenium to form an aluminum ruthenium mixture, so that the back electric field structure 4 is formed at the back surface 22, thus completing the fabrication of the battery.

According to the present invention, the glass content ratio of the first slurry 5' is greater than the second slurry 6' by an appropriate glass content limitation, so that the first slurry 5' is more aggressive and can be surely bonded to the substrate. The ruthenium reaction makes the back electric field structure 4 formed by sintering have sufficient thickness and good quality. On the other hand, the second slurry 6' has a low glass content ratio, and the etching property to the dielectric layer 3 is relatively small, so that the damage to the dielectric layer 3 can be alleviated.

Please refer to Table 1 for the results of testing various characteristics of the solar cell of the present invention and the solar cell of the comparative example. The back electrode of the battery of the comparative example is formed by screen printing of a single aluminum paste material, and the material composition thereof is the same as that of the present invention. The two conductive adhesive layers 6 are the same.

V _oc in the table represents the open circuit voltage, J _sc represents the short circuit current, R _s represents the series resistance, R _sh represents the parallel resistance, FF value represents the fill factor, and Eff. is the conversion efficiency. As can be seen from the results of Table 1, the present invention effectively reduces the series resistance with respect to the comparative example, and has a large open circuit voltage, a short circuit current, a parallel resistance, an FF value, and a conversion efficiency. This is because the present invention can produce a thick back electric field structure 4 by increasing the glass content and the aggressiveness of the first paste 5' (which is also equivalent to the first conductive adhesive layer 5 formed therein). Since the second slurry 6' of the present invention (which also corresponds to the second conductive paste layer 6 formed therein) has a low glass content, the quality of the dielectric layer 3 can be achieved.

In summary, the back electrode of the battery is formed by two materials, and the glass content in the material is adjusted according to the position and function of the first conductive adhesive layer 5 and the second conductive adhesive layer 6. The material has different etching ability, so on the one hand, the back electric field structure 4 with thick thickness and good quality can be formed, and on the other hand, the quality and function of the dielectric layer 3 can be maintained, thereby improving the open circuit voltage and conversion efficiency of the battery. . The invention has good applicability, and can adjust the composition of each conductive adhesive layer according to different requirements. For example, if the glass content in the second conductive adhesive layer 6 is further reduced, the quality of the dielectric layer 3 will be further improved. it is good.

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. . . Photoelectric conversion unit

twenty one. . . Glossy surface

twenty two. . . back

3. . . Dielectric layer

31. . . First side

32. . . Second side

33. . . perforation

4. . . Back electric field structure

5. . . First conductive adhesive layer

5’. . . First slurry

51. . . Conductive contact

52. . . Conductive protrusion

6. . . Second conductive adhesive layer

6’. . . Second slurry

71~74. . . step

1 is a schematic view showing a manufacturing process of a known solar cell;

Figure 2 is a cross-sectional view showing a preferred embodiment of the solar cell of the present invention;

3 is a flow block diagram showing a preferred embodiment of a method of fabricating a solar cell of the present invention;

Figure 4 is a schematic view showing the manufacturing process of the preferred embodiment.

2. . . Photoelectric conversion unit

twenty one. . . Glossy surface

twenty two. . . back

3. . . Dielectric layer

31. . . First side

32. . . Second side

33. . . perforation

4. . . Back electric field structure

5. . . First conductive adhesive layer

51. . . Conductive contact

52. . . Conductive protrusion

6. . . Second conductive adhesive layer

Claims (10)

A solar cell comprising: a photoelectric conversion unit for converting light energy into electrical energy, and comprising an opposite light incident surface and a back surface; a dielectric layer disposed adjacent to the back surface and including a plurality of perforations; a back electric field structure, corresponding to the perforation, located at a back surface of the photoelectric conversion unit; a first conductive adhesive layer containing a glass material, comprising a plurality of conductive layers respectively located in the perforations and contacting the back electric field structure a contact portion; and a second conductive adhesive layer containing a glass material, coated on the dielectric layer, and the second conductive adhesive layer has a glass content ratio smaller than a glass content ratio of the first conductive adhesive layer. The solar cell of claim 1, wherein the first conductive adhesive layer and the second conductive adhesive layer are formed by screen printing of a metal paste. The solar cell according to claim 2, wherein the metal paste is an aluminum paste. The solar cell of claim 3, wherein the first conductive adhesive layer further comprises a plurality of conductive protrusions each protruding from the conductive contact and spaced apart from each other. The solar cell of claim 1, wherein the second conductive adhesive layer is an aluminum conductive adhesive layer, and the second conductive adhesive layer has a thickness of 20 μm to 30 μm. A method of manufacturing a solar cell comprising: step A: forming a dielectric layer having a plurality of perforations on a back surface of a photoelectric conversion unit; and step B: coating a portion on the dielectric layer corresponding to the perforation a first slurry; step C: coating a second slurry on the dielectric layer and the first slurry, and a glass content ratio of the second slurry is less than a glass content ratio of the first slurry; Step D: performing sintering to form the first slurry to form a first conductive adhesive layer, the second paste forming a second conductive adhesive layer, and forming a plurality of corresponding perforations corresponding to the photoelectric conversion unit The back electric field structure at the back. The method of manufacturing a solar cell according to claim 6, wherein the first slurry comprises 2 wt% to 7 wt% of a glass material, and the second paste comprises 1 wt% to 5 wt% of a glass material. The method for manufacturing a solar cell according to claim 6, wherein the second slurry is an aluminum paste, and in step D, the second conductive adhesive layer formed after sintering has a thickness of 20 μm to 30 μm. . The method for producing a solar cell according to any one of claims 6 to 8, wherein the first slurry and the second slurry are applied by screen printing. The method for manufacturing a solar cell according to claim 9, wherein in the step B, after the first slurry is applied, a baking step is further performed to dry and shape the first slurry.