LAMINATED PASSIVATION STRUCTURE OF SOLAR CELL AND PREPARATION METHOD THEREOF

Abstract

A laminated passivation structure of solar cell and a preparation method thereof are disclosed herein. The laminated passivation structure of solar cell includes a P-type silicon substrate, a first dielectric layer, a second dielectric layer, and a third dielectric layer sequentially arranged on the back side of the P-type silicon substrate from inside to outside. The preparation method includes generating a first dielectric layer on the back surface of the P-type silicon substrate, and then sequentially depositing a second dielectric layer and a third dielectric layer on the first dielectric layer.

Claims

1. A laminated passivation structure of solar cell comprising a P-type silicon substrate (1), and a first dielectric layer (2), a second dielectric layer (3), and a third dielectric layer (4) sequentially arranged on the back surface of the P-type silicon substrate (1) from inside to outside.

2. The laminated passivation structure of solar cell according to claim 1, wherein the first dielectric layer (2) comprises a silicon-containing layer.

3. The laminated passivation structure of solar cell according to claim 1, wherein the first dielectric layer (2) is a silicon oxide layer.

4. The laminated passivation structure of solar cell according to claim 1, wherein the thickness of the first dielectric layer (2) is 1 to 10 nm.

5. The laminated passivation structure of solar cell according to claim 1, wherein the second dielectric layer (3) comprises a silicon-containing layer.

6. The laminated passivation structure of solar cell according to claim 1, wherein the second dielectric layer (3) is any one or a combination of at least two of a silicon oxynitride layer, a silicon nitride layer, and a silicon carbide layer.

7. The laminated passivation structure of solar cell according to claim 1, wherein the thickness of the second dielectric layer (3) is 1 to 150 nm.

8. The laminated passivation structure of solar cell according to claim 1, wherein the second dielectric layer (3) is deposited by a PECVD method with a thickness of 1 to 100 nm.

9. The laminated passivation structure of solar cell according to claim 1, wherein the refractive index of the second dielectric layer (3) is 1.5 to 2.4.

10. The laminated passivation structure of solar cell according to claim 1, wherein the second dielectric layer (3) is a laminated film structure with different refractive indexes.

11. The laminated passivation structure of solar cell according to claim 10, wherein the second dielectric layer (3) is a laminated film structure of silicon oxynitride with a refractive index ranging from 1.6 to 2.2 and silicon oxynitride with a refractive index ranging from 1.7 to 2.4.

12. The laminated passivation structure of solar cell according to claim 10, wherein the second dielectric layer (3) is a laminated film structure of silicon oxynitride with a refractive index ranging from 1.6 to 2.2 and silicon carbide with a refractive index ranging from 1.7 to 2.4.

13. The laminated passivation structure of solar cell according to claim 10, wherein in the laminated film structure of the second dielectric layer (3), along a direction away from the P-type silicon substrate (1), the refractive indexes of each film of the laminated film increase in sequence.

14. The laminated passivation structure of solar cell according to claim 1, wherein the third dielectric layer (4) comprises a silicon-containing layer.

15. The laminated passivation structure of solar cell according to claim 1, wherein the third dielectric layer (4) is any one or a combination of at least two of a silicon oxide layer, a silicon oxynitride layer, a silicon nitride layer, and a silicon carbide layer.

16. The laminated passivation structure of solar cell according to claim 1, wherein the thickness of the third dielectric layer (4) is 1 to 200 nm.

17. The laminated passivation structure of solar cell according to claim 1, wherein the third dielectric layer (4) is deposited by a PECVD method with a thickness of 10 to 150 nm.

18. The laminated passivation structure of solar cell according to claim 1, wherein the refractive index of the third dielectric layer (4) is 1.5 to 2.4.

19. The laminated passivation structure of solar cell according to claim 1, wherein the third dielectric layer (4) is a laminated film structure with different refractive indexes.

20. The laminated passivation structure of solar cell according to claim 19, wherein the third dielectric layer (4) is a laminated film structure of silicon nitride with a refractive index ranging from 1.6 to 2.2 and silicon nitride with a refractive index ranging from 1.9 to 2.4.

21. The laminated passivation structure of solar cell according to claim 19, wherein in the laminated film structure of the third dielectric layer (4), along a direction away from the P-type silicon substrate (1), the refractive indexes of each film of the laminated film increase in sequence.

22. The structure according to claim 1, wherein the first dielectric layer (2) is a silicon oxide layer with a thickness of 1 to 10 nm, the second dielectric layer (3) is a silicon oxynitride layer with a thickness of 1 to 80 nm, and the third dielectric layer (4) is a silicon nitride layer with a thickness of 1 to 100 nm.

23. The structure according to claim 1, wherein the first dielectric layer (2) is a silicon oxide layer with a thickness of 1 to 10 nm, the second dielectric layer (3) is a silicon carbide layer with a thickness of 1 to 80 nm, and the third dielectric layer (4) is a silicon nitride layer with a thickness of 1 to 100 nm.

24. The laminated passivation structure of solar cell according to claim 1, wherein the laminated passivation structure of solar cell further comprises a N.sup.++ heavily diffused region (7), a N.sup.+ lightly diffused region (8), a fourth dielectric layer (9) and a fifth dielectric layer (6) sequentially arranged on the front surface of the P-type silicon substrate (1) from inside to outside.

25. The laminated passivation structure of solar cell according to claim 24, wherein the fourth dielectric layer (9) is a SiO.sub.2 layer.

26. The laminated passivation structure of solar cell according to claim 24, wherein the thickness of the fourth dielectric layer (9) is 1 to 10 nm.

27. The laminated passivation structure of solar cell according to claim 24, wherein the fifth dielectric layer (6) is any one or a combination of at least two of a silicon oxide layer, a silicon oxynitride layer, a silicon nitride layer, and a silicon carbide layer.

28. The laminated passivation structure of solar cell according to claim 24, wherein the thickness of the fifth dielectric layer (6) is a SiN.sub.x layer with a thickness of 25 to 100 nm.

29. The laminated passivation structure of solar cell according to claim 24, wherein the laminated passivation structure of solar cell further comprises a front Ag electrode (10) contacting with the N.sup.++ heavily diffused region (7) through the fifth dielectric layer (6) and the fourth dielectric layer (9).

30. The laminated passivation structure of solar cell according to claim 1, wherein the laminated passivation structure of solar cell further comprises an aluminum back field (5) connecting with the P-type silicon substrate (1) after passing through the third dielectric layer (4), the second dielectric layer (3), and the first dielectric layer (2).

31. The laminated passivation structure of solar cell according to claim 24, wherein the diffusion sheet resistance of the N.sup.+ lightly diffused region (8) is 120 to 300 ohm/sq.

32. The laminated passivation structure of solar cell according to claim 24, wherein the diffusion sheet resistance of the N.sup.++ heavily diffused region (7) is 40 to 100 ohm/sq.

33. The laminated passivation structure of solar cell according to claim 1, wherein the front surface of the P-type silicon substrate is sequentially provided with an emitter junction region and a first SiN.sub.x film from inside to outside, a Ag electrode passes through the first SiN.sub.x film and then connects with the emitter junction region, the back surface of the P-type silicon substrate is sequentially provided with a second SiO.sub.2 film, a SiO.sub.xN.sub.y film and a second SiN.sub.x film from inside to outside, an aluminum back field (5) passes through the second SiN.sub.x film, the SiO.sub.xN.sub.y film and the second SiO.sub.2 film in sequence and then contacts with the P-type silicon substrate.

34. The laminated passivation structure of solar cell according to claim 33, wherein the thickness of the second SiO.sub.2 film is 0 to 10 nm.

35. The laminated passivation structure of solar cell according to claim 33, wherein the SiO.sub.xN.sub.y film is deposited by a PECVD method, and has a thickness of 1 to 100 nm.

36. The laminated passivation structure of solar cell according to claim 33, wherein the second SiN.sub.x film is a SiN.sub.x film deposited by a PECVD method, and has a thickness of 10 to 150 nm.

37. The laminated passivation structure of solar cell according to claim 33, wherein the thickness of the second SiN.sub.x film is 10 to 150 nm.

38. The laminated passivation structure of solar cell according to claim 33, wherein the SiO.sub.xN.sub.y film is a SiO.sub.xN.sub.y laminated film with different refractive indexes.

39. The laminated passivation structure of solar cell according to claim 33, wherein the second SiN.sub.x film is a separate SiN.sub.x passivation layer or a SiN.sub.x laminated film with different refractive indexes.

40. The laminated passivation structure of solar cell according to claim 33, wherein the emitter junction region comprises a N.sup.++ heavily diffused region (7), a N.sup.+ lightly diffused region (8) and a first SiO.sub.2 film which are arranged on the front surface of the P-type silicon substrate (1) from inside to outside.

41. The laminated passivation structure of solar cell according to claim 40, wherein the diffusion sheet resistance of the N.sup.+ lightly diffused region (8) is 120 to 180 ohm/sq, and the diffusion sheet resistance of the N.sup.++ heavily diffused region (7) is 40 to 100 ohm/sq.

42. The laminated passivation structure of solar cell according to claim 33, wherein the thickness of the first SiO.sub.2 film is 1 to 10 nm, and the first SiN.sub.x film has a thickness of 25 to 100 nm.

43. A method for preparing a laminated passivation structure of solar cell according to claim 1, wherein the method comprises the following steps: generating a first dielectric layer (2) on the back surface of the P-type silicon substrate (1), and then sequentially depositing a second dielectric layer (3) and a third dielectric layer (4) on the first dielectric layer (2).

44. The method according to claim 43, wherein the growth method of the first dielectric layer (2) is a thermal oxidation method, a solution method or a PECVD method.

45. The method according to claim 43, wherein the second dielectric layer (3) is deposited by a PECVD method.

46. The method according to claim 43, wherein the third dielectric layer (4) is deposited by a PECVD method.

47. The method for preparing (Original) The laminated passivation structure of solar cell according to claim 43, wherein the method further comprises: preparing a N.sup.++ heavily diffused region (7) and a N.sup.+ lightly diffused region (8), and depositing a fourth dielectric layer (9) and a fifth dielectric layer (6).

48. The method according to claim 47, wherein the fourth dielectric layer (9) is deposited by a PECVD method.

49. The method according to claim 47, wherein the fifth dielectric layer (6) is deposited by a PECVD method.

50. The method for preparing (Original) The laminated passivation structure of solar cell according to claim 43, wherein the method comprises the following steps: removing the mechanical damaged layer of a P-type silicon substrate (1) with an alkaline etching solution, and then etching the surface of the silicon substrate (1) by use of the alkaline etching solution to form a pyramid structure on the front side of the P-type silicon substrate (1), after that, performing diffusion to form a N.sup.+ lightly diffused region (8) on the front side of the P-type silicon substrate (1), and performing laser doping to obtain a N.sup.++ heavily diffused region (7), removing the back junction of the P-type silicon substrate (1), and polishing the back surface of the P-type silicon substrate (1), oxidation generating a first dielectric layer (2) and a fourth dielectric layer (9) on the P-type silicon substrate (1), and then sequentially depositing a second dielectric layer (3), and a third dielectric layer (4) on the first dielectric layer (2), and depositing a fifth dielectric layer (6) on the fourth dielectric layer (9); printing a back Ag electrode and drying, then printing a back Al paste to form an aluminum back field (5), and printing a front Ag electrode (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 is a schematic diagram of a laminated passivation structure of solar cell provided in Example 1, wherein:

[0074] FIGS. 1A-1G show schematic diagrams of the solar cells in different stages according to the preparation method of Example 1 (the front surface of the cell is a textured structure, and is intentionally drawn as a plane for simple illustration) in which: [0075] 1-P-type silicon substrate, [0076] 2-first dielectric layer, [0077] 3-second dielectric layer, [0078] 4-third dielectric layer, [0079] 6- fifth dielectric layer, [0080] 7-N.sup.++ heavily diffused region, [0081] 8- N.sup.+ lightly diffused region, [0082] 9- fourth dielectric layer.

[0083] FIG. 2 shows a schematic cross-sectional view of the laminated passivation structure of solar cell provided in Example 1 (the front surface of the cell is a textured structure, and is intentionally drawn as a plane for simple illustration) in which: [0084] 1-P-type silicon substrate, [0085] 2-first dielectric layer, [0086] 3-second dielectric layer, [0087] 4-third dielectric layer, [0088] 5-aluminum back field, [0089] 6- fifth dielectric layer, [0090] 7-N.sup.++ heavily diffused region, [0091] 8- N.sup.+ lightly diffused region, [0092] 9-fourth dielectric layer, [0093] 10- front Ag electrode.

[0094] FIG. 3 shows a schematic cross-sectional view of the laminated passivation structure provided of solar cell in Example 1 (the front surface of the cell is a textured structure, and is intentionally drawn as a plane for simple illustration) in which: [0095] 1-P-type silicon substrate, [0096] 2- first dielectric layer, [0097] 3-second dielectric layer, [0098] 4- third dielectric layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0099] In order to better explain the present application and facilitate the understanding of the technical solutions of the present application, the present application will be further described in detail below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the claims of the present application, which is subject to the claims.

[0100] In the present application, as a specific embodiment, the laminated passivation structure of solar cell comprises: a P-type silicon substrate, and the front surface of the P-type silicon substrate is sequentially provided with an emitter junction region and a first SiN.sub.x film from inside to outside, a Ag electrode passes through the first SiN.sub.x film and then connects with the emitter junction region, the back surface of the P-type silicon substrate is sequentially provided with a second SiO.sub.2 film, a SiO.sub.xN.sub.y film and a second SiN.sub.x film from inside to outside, an aluminum back field passes through the second SiN.sub.x film, the SiO.sub.xN.sub.y film and the second SiO.sub.2 film in sequence and then contacts with the P-type silicon substrate.

[0101] The emitter junction region includes a N.sup.++ heavily diffused region, a N.sup.+ lightly diffused region and a first SiO.sub.2 film which are arranged on the front surface of the P-type silicon substrate from inside to outside.

[0102] The thickness of the second SiO.sub.2 film is 0 to 10 nm. The SiO.sub.xN.sub.y film is deposited by a PECVD method, with a thickness of 1 to 100 nm. The second SiN.sub.x film is a SiN.sub.x layer deposited by a PECVD method, and has a thickness of 10 nm to 150 nm. The second SiN.sub.x film has a thickness of 10 nm to 150 nm. The first SiO.sub.2 film has a thickness of 0 to 10 nm, and the first SiN.sub.x film has a thickness of 25 to 100 nm.

[0103] The second SiO.sub.xN.sub.y film is a separate SiO.sub.xN.sub.y passivation layer or a SiO.sub.xN.sub.y laminated film with different refractive indexes.

[0104] The second SiN.sub.x film is a separate SiN.sub.x passivation layer or a SiN.sub.x laminated film with different refractive indexes.

[0105] The diffusion sheet resistance of the N.sup.+ lightly diffused region is 120 to 180 ohm/sq, and the diffusion sheet resistance of the N.sup.++ heavily diffused region is 40 to 100 ohm/sq.

[0106] In this embodiment, the film on the back surface of the P-type silicon substrate contains a large amount of H.sup.+, which will be injected into the surface and the interior of the silicon wafer during the subsequent annealing process or sintering process to passivate the recombination center.

[0107] As another specific embodiment, the laminated passivation structure of solar cell comprises: a P-type silicon substrate, and the front surface of the P-type silicon substrate is sequentially provided with an emitter junction region and a first SiN.sub.x film from inside to outside, a Ag electrode passes through the first SiN.sub.x film and then connects with the emitter junction region, the back surface of the P-type silicon substrate is sequentially provided with a second SiO.sub.2 film, a SiO.sub.xN.sub.y film and a second SiN.sub.x film from inside to outside, an aluminum back field passes through the second SiN.sub.x film, the SiO.sub.xN.sub.y film and the second SiO.sub.2 film in sequence and then contacts with the P-type silicon substrate. The emitter junction region 2 includes a N.sup.++ heavily diffused region, a N.sup.+ lightly diffused region and a first SiO.sub.2 film which are arranged on the front surface of the P-type silicon substrate from inside to outside.

[0108] Specifically, 47% by volume of a potassium hydroxide (KOH) solution is used to remove the mechanical damaged layer of the P-type silicon substrate by 2 to 3 .Math.m, and then 47% by volume of a KOH solution is used to etch the surface of the silicon wafer to form a pyramid structure of 2 to 3 .Math.m.

[0109] POCl.sub.3 liquid-low-pressure diffusion is used to form a p-n junction, i.e. a N.sup.+ lightly diffused region, the diffusion temperature is 810° C., the process time is 90 min, and the diffusion sheet resistance is controlled as 120 to 180 ohm/sq.

[0110] Laser selective emitter (SE) doping, the phosphorous atoms in the phosphorosilicate glass after the diffusion is laser doped by the high temperature of laser to form a local heavy doping region, which is the N.sup.++ heavily diffused region with a diffusion sheet resistance of 40 to 100 ohm/sq.

[0111] The back junction of the P-type silicon substrate is removed by a chain cleaning machine, and the back surface of the silicon wafer is polished by 3 to 4 .Math.m to remove the peripheral p-n junction.

[0112] Oxidation is conducted on the front surface, the back surface, and the edges of the P-type silicon substrate wafer to generate thin SiO.sub.2 films, which are the first SiO.sub.2 film and the second SiO.sub.2 film with a thickness of 0 to 10 nm.

[0113] The back-surface SiO.sub.xN.sub.y film is deposited by PECVD, with a thickness of 1 to 100 nm.

[0114] The back-surface second SiN.sub.x film is deposited by PECVD, with a thickness of 10 to 150 nm.

[0115] The front-surface first SiN.sub.x film is deposited by PECVD, with a thickness of 25 to 100 nm.

[0116] A 532 nm ns laser is used to make local grooving on the back laminated film to open the laminated passivation film.

[0117] After a back Ag electrode is printed and dried, a back Al paste is then printed.

[0118] A front Ag cell is printed and quickly sintered at 875° C. to form a good ohmic contact of Ag electrode.

[0119] As yet another specific embodiment, the laminated passivation structure of solar cell comprises: a P-type silicon substrate, and the front surface of the P-type silicon substrate is sequentially provided with an emitter junction region and a first SiN.sub.x film from inside to outside, a Ag electrode passes through the first SiN.sub.x film and then connects with the emitter junction region, the back surface of the P-type silicon substrate is sequentially provided with a SiO.sub.xN.sub.y film, and a second SiN.sub.x film from inside to outside, an aluminum back field passes through the second SiN.sub.x film, and the SiO.sub.xN.sub.y film in sequence and then contacts with the P-type silicon substrate. The emitter junction region includes a N.sup.++ heavily diffused region, a N.sup.+ lightly diffused region and a first SiO.sub.2 film which are arranged on the front surface of the P-type silicon substrate 1 from inside to outside.

[0120] 47% by volume of a KOH solution is used to remove the mechanical damaged layer of the P-type substrate by 2 to 3 .Math.m, and then 47% by volume of a KOH solution is used to etch the surface of the silicon wafer to form a pyramid structure of 2 to 3 .Math.m.

[0121] POCl.sub.3 liquid-low-pressure diffusion is used to form a N.sup.+ lightly diffused region, the diffusion temperature is 810° C., the process time is 90 min, and the diffusion sheet resistance is controlled as 120 to 180 ohm/sq.

[0122] Laser SE doping, the phosphorous atoms in the phosphorosilicate glass after the diffusion is laser doped by the high temperature of laser to form a local N.sup.++ heavily diffused region, and the diffusion sheet resistance is 40 to 100 ohm/sq.

[0123] The back junction is removed by a chain cleaning machine, and the back surface of the silicon wafer is polished by 3 to 4 .Math.m to remove the peripheral p-n junction.

[0124] Oxidation is conducted on the front surface and the edges of the silicon wafer to generate a thin SiO.sub.2 film, which is a first SiO.sub.2 film with a thickness of 0 to 10 nm.

[0125] The back-surface SiO.sub.xN.sub.y film and the second SiN.sub.x film are deposited by PECVD, with thicknesses of 1 to 100 nm and 10 to 150 nm, respectively. The front-surface first SiN.sub.x film is deposited by PECVD, with a thickness of 25 to 100 nm.

[0126] A 532 nm ns laser is used to make local grooving on the back laminated film to open the laminated passivation film.

[0127] After a back Ag electrode is printed and dried, a back Al paste is then printed. A front Ag cell is printed and quickly sintered at 875° C. to form a good ohmic contact.

[0128] The following are typical but non-limiting examples of the present application:

Example 1

[0129] This example provides a laminated passivation structure of solar cell, as shown in FIG. 2 and FIG. 3. The passivation structure of solar cell includes a P-type silicon substrate 1, and the back surface of the P-type silicon substrate 1 is sequentially provided with a first dielectric layer 2, a second dielectric layer 3, and a third dielectric layer 4, an aluminum back field 5 connecting with the P-type silicon substrate 1 after passing through the third dielectric layer 4, the second dielectric layer 3, and the first dielectric layer 2 in sequence, a N.sup.++ heavily diffused region 7, a N.sup.+ lightly diffused region 8, a fourth dielectric layer 9 and a fifth dielectric layer 6 sequentially arranged on the front surface of the P-type silicon substrate 1 from inside to outside. The laminated passivation structure of solar cell provided in this example further includes a front Ag electrode 10, and the front Ag electrode 10 passes through the fifth dielectric layer 6 and the fourth dielectric layer 9 into the N.sup.++ heavily diffused region 7.

[0130] In the laminated passivation structure of solar cell provided in this example, the first dielectric layer 2 is a silicon oxide film with a thickness of 2 nm, the second dielectric layer 3 is a silicon oxynitride laminated film with a total thickness of 20 nm and a refractive index of 1.7, the third dielectric layer 4 is a silicon nitride laminated film with a total thickness of 70 nm and a refractive index of 2.1, the diffusion sheet resistance of the N.sup.+ lightly diffused region 8 is 150 ohm/sq, the diffusion sheet resistance of the N.sup.++ heavily diffused region 7 is 75 ohm/sq, the fourth dielectric layer 9 is a silicon oxide film with a thickness of 2 nm, and the fifth dielectric layer 6 is a silicon nitride film with a thickness of 75 nm and a refractive index of 2.0.

[0131] The second dielectric layer 3 is a three-layer silicon oxynitride laminated film, and along the direction away from the P-type silicon substrate 1 there are a first film of the second dielectric layer 3, a second film of the second dielectric layer 3, and a third film of the second dielectric layer 3, respectively. The refractive index of the first film of the second dielectric layer 3 is 1.7, the refractive index of the second film of the second dielectric layer 3 is 1.8, and the refractive index of the third film of the second dielectric layer 3 is 1.9.

[0132] The third dielectric layer 4 is a three-layer silicon nitride laminated film, and along the direction away from the P-type silicon substrate 1 there are a first film of the third dielectric layer 4, a second film of the third dielectric layer 4, and a third film of the third dielectric layer 4, respectively. The refractive index of the first film of the third dielectric layer 4 is 2.0, the refractive index of the second film of the third dielectric layer (4) is 2.1, and the refractive index of the third film of the third dielectric layer (4) is 2.2.

[0133] In the laminated passivation structure of solar cell provided in this example, the N.sup.+ lightly diffused region 8 is obtained by a tubular liquid phosphorous source diffusion, and the N.sup.++ heavily diffused region 7 is obtained by laser doping.

[0134] A method for preparing the laminated passivation structure of solar cell provided in this example, and the specific steps include: [0135] (1) Using 2% by mass of a KOH solution to remove the mechanical damaged layer of the P-type silicon wafer by 1.5 .Math.m, and then using 3% by mass of a KOH solution to etch the surface of the silicon wafer to form a pyramid structure with a size of 1.5 .Math.m. [0136] (2) Using POCl.sub.3 liquid diffusion to form a N.sup.+ lightly diffused region 8, with the diffusion temperature being 810° C., and the process time being 90 min. [0137] (3) Laser SE doping, laser doping the phosphorous atoms in the phosphorosilicate glass after the diffusion by the high temperature of laser to form a local N.sup.++ heavily diffused region 7. [0138] (4) Removing the back junction by a chain cleaning machine, and polishing the back surface of the silicon wafer by 3.5 .Math.m to remove the peripheral p-n junction. [0139] (5) Generating thin silicon oxide films on the back surface, the front surface, and the edges of the silicon wafer by thermal oxidation, i.e. the first dielectric layer 2 and the fourth dielectric layer 9, with a thickness of 2 nm. [0140] (6) Depositing a silicon oxynitride film on the back surface by PECVD, i.e. the second dielectric layer 3; depositing a silicon nitride film on the back surface by PECVD, i.e. the third dielectric layer 4. [0141] (7) Depositing a silicon nitride film on the front surface by PECVD, i.e. the fifth dielectric layer 6. [0142] (8) Using a 532 nm ns laser to make local grooving on the back laminated film to open the laminated passivation film. [0143] (9) After printing a back Ag paste and drying, and then printing a back Al paste 5 and drying, printing a front Ag paste 10 and quickly sintering at 875° C. to form a good ohmic contact.

[0144] FIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D, FIG. 1E, FIG. 1F, and FIG. 1G are schematic diagrams of solar cells in different stages according to the above-mentioned preparation methods.

Example 2

[0145] The laminated passivation structure of solar cell provided in this example refers to Example 1, and the differences lie in that the first dielectric layer 2 is a silicon oxide film with a thickness of 2 nm, the second dielectric layer 3 is a laminated film consisting of a silicon oxynitride film, a silicon nitride film and a silicon carbide film with a total thickness of 20 nm and a refractive index of 1.7, the third dielectric layer 4 is a two-layer silicon nitride film with thicknesses of 20 nm and 40 nm, respectively, the diffusion sheet resistance of the N.sup.+ light diffusion region 8 is 150 ohm/sq, the diffusion sheet resistance of the N.sup.++ heavy diffusion region 7 is 75 ohm/sq, the fourth dielectric layer 9 is a SiO.sub.2 film with a thickness of 2 nm, and the fifth dielectric layer 6 is a silicon nitride film with a thickness of 75 nm and a refractive index of 2.0.

[0146] The second dielectric layer 3 is a laminated film consisting of a silicon oxynitride film, a silicon nitride film and a silicon carbide film, and along the direction away from the P-type silicon substrate 1 there are a first film of the second dielectric layer 3 (a silicon oxynitride film), a second film of the second dielectric layer 3 (a silicon nitride film), and a third film of the second dielectric layer 3 (a silicon carbide film), respectively. The refractive index of the first film of the second dielectric layer 3 is 1.7, the refractive index of the second film of the second dielectric layer 3 is 1.9 and the refractive index of the third film of the second dielectric layer 3 is 2.0.

[0147] The third dielectric layer 4 is a two-layer silicon nitride film, and along the direction away from the P-type silicon substrate 1 there are a first film of the third dielectric layer 4 and a second film of the third dielectric layer 4, respectively. The refractive index of the first film of the third dielectric layer 4 is 2.0, and the refractive index of the second film of the third dielectric layer 4 is 2.1.

[0148] A method for preparing the laminated passivation structure of solar cell provided in this example, and the specific steps include: [0149] (1) Using 2% by mass of a KOH solution to remove the mechanical damaged layer of the P-type silicon wafer by 1.5 .Math.m, and then using 3% by mass of a KOH solution to etch the surface of the silicon wafer to form a pyramid structure with a size of 1.5 .Math.m. [0150] (2) Using POCl.sub.3 liquid diffusion to form a N.sup.+ lightly diffused region 8, with the diffusion temperature being 810° C., and the process time being 90 min. [0151] (3) Laser SE doping, laser doping the phosphorous atoms in the phosphorosilicate glass after the diffusion by the high temperature of laser to form a local N.sup.++ heavily diffused region 7. [0152] (4) Removing the back junction by a chain cleaning machine, and polishing the back surface of the silicon wafer by 3.5 .Math.m to remove the peripheral p-n junction. [0153] (5) Generating thin silicon oxide films on the back surface, the front surface, and the edges of the silicon wafer by thermal oxidation, i.e. the first dielectric layer 2 and the fourth dielectric layer 9, with a thickness of 2 nm. [0154] (6) Depositing a silicon oxynitride film, a silicon nitride film and a silicon carbide film on the back surface by PECVD, i.e. the second dielectric layer 3; depositing a two-layer silicon nitride film on the back surface by PECVD, i.e. the third dielectric layer 4. [0155] (7) Depositing a silicon nitride film on the front surface by PECVD, i.e. the fifth dielectric layer 6. [0156] (8) Using a 532 nm ns laser to make local grooving on the back laminated film to open the laminated passivation film. [0157] (9) After printing a back Ag paste and drying, and then printing a back Al paste 5 and drying, printing a front Ag paste 10 and quickly sintering at 875° C. to form a good ohmic contact.

Comparative Example 1

[0158] The difference between this comparative example and Example 1 lies in that the laminated passivation structure of solar cell provided by this comparative example isn’t provided with the first dielectric layer 2.

Comparative Example 2

[0159] The difference between this comparative example and Example 1 lies in that the laminated passivation structure of solar cell provided by this comparative example isn’t provided with the second dielectric layer 3.

Comparative Example 3

[0160] The difference between this comparative example and Example 2 lies in that the laminated passivation structure of solar cell provided by this comparative example isn’t provided with the third dielectric layer 4 of the laminated structure.

[0161] The results of cells in different solutions are shown in the table below:

TABLE-US-00001 Open-circuit voltage Short-circuit current Fill factor Conversion efficiency [mV] [mA/cm.sup.2] [%] [%] Example 1 690 40.7 81.5 22.89 Comparative Example 1 688 40.68 81.45 22.80 Comparative 688 40.6 81.45 22.75 Example 2 Example 2 690 40.8 81.5 22.94 Comparative Example 3 690 40.7 81.5 22.89

[0162] The above efficiency tests of the cell is under the standard test conditions: Irradiance 1000 W/m.sup.2, Cell Temperature 25° C., Air Mass AM1.5

[0163] Compared with Example 1, since Comparative Example 1 is not provided with the first dielectric layer 2, a weakened chemical passivation effect is resulted, the cell Voc is lowered by 2 mV and the efficiency is lowered by 0.09%.

[0164] Compared with Example 1, since Comparative Example 2 is not provided with the second dielectric layer 3, a weakened back light reflection effect is resulted, at the same time the bombardment of the first dielectric layer (2) by the high-power plasma during the deposition of the third dielectric layer (4) cann’t be weakened, the open-circuit voltage of the cell is lowered by 2 mV, the current density is lowered by 0.1 mA/cm.sup.2 and the efficiency is lowered by 0.14%.

[0165] Compared with Example 2, since Comparative Example 3 is not provided with the third dielectric layer 4 of the laminated structure, a weakened back light reflection effect is resulted, the current density is lowered by 0.1 mA/cm.sup.2 and the efficiency is lowered by 0.05%.

[0166] Based on the above results, it can be seen that the back laminated passivation structure of solar cell provided in Examples 1-2 has very good chemical passivation and back reflection effects.

[0167] The applicant declares that the present application illustrates the detailed methods of the present application through the above-mentioned examples, but the present application is not limited thereto, that is, it doesn’t meant that the present application can only be implemented depending on the above-mentioned detailed methods.