Solar cell and method for production thereof

• US 20040187916A1
• Filed: 02/19/2004
• Published: 09/30/2004
• Est. Priority Date: 08/31/2001
• Status: Abandoned Application

• Current Assignee: Rudolf Hezel
• Original Assignee: Rudolf Hezel
• Inventors: Hezel, Rudolf
• Application Number:
  US10/486,821
• Publication Number:
  US 20040187916A1
• Time in Patent Office: Days
• US Class Current: 136/256
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact solar cells
• CPC Class Codes: H01L 31/0236 Special surface textures
• CPC Class Codes: H01L 31/02363 of the semiconductor body itself, e.g. textured active layers
• CPC Class Codes: H01L 31/035281 Shape of the body
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

The invention relates to a method for production of a solar cell (10) and said cell. According to the invention, a high efficiency may be achieved, whereby, on the rear side of the solar cell, first and second contacts (26, 28) are arranged on projections (18), or the flanks thereof (20, 22), for collecting minority and majority charge carriers.

Claims

1. Solar cell (10) including a semiconductor substrate (16) with first and second contacts (26, 28;

58, 60;

80, 82;

106, 108;

132) for collecting and discharging minority and majority charge carriers generated by incident radiation energy in the semiconductor substrate, whereby at least the back surface of the semiconductor substrate has line or bar-like elevations (18, 50, 52, 54, 56, 78, 104, 130, 140) with respectively first and second longitudinal flanks (20, 22, 62, 74, 76, 110, 112) running parallel, whereby the first and second contacts are arranged on the back surface of the semiconductor substrate spaced from one another, wherein the first and second longitudinal flank (20, 22, 62, 64, 74, 76, 110, 112) of the elevation (18, 50, 52, 54, 56, 78, 104, 130, 140) pass over into one another through an outer segment (24, 72, 86, 114) running parallel or approximately parallel to the plane spanned by the semiconductor substrate (16), wherein on at least some of the elevations, the first contacts (26, 58, 80, 106) extend on the first longitudinal flanks (22, 62, 74, 110) of the elevations and the second contacts (28, 60, 82, 108) on the second longitudinal flanks (20, 64, 76, 112) of the elevations, and wherein the first and second contacts are spaced from one another on the trench side as well as on the exterior segment side.

2. Solar cell according to claim 1, wherein the elevations (18, 50, 52, 54, 56, 78, 104, 130, 140) have a U, V or sawtooth shape in section, wherein the trench bottom runs at least segment-wise parallel or approximately parallel to the plane spanned by the semiconductor substrate (16) and wherein the first or second contact (26, 58, 80, 106;

28, 60, 82, 108) preferably extend up to the outer rim (102, 104) of the first or second longitudinal flank (20, 22, 62, 64, 74, 76, 110, 112) of the elevation as well as up to the trench bottom, or spaced from the latter.

4. Solar cell according to at least claim 1, wherein the contact (58, 80, 106) collecting the minority charge carriers is a metal/semiconductor and/or a MIS (metal insulator semiconductor) contact.

5. Solar cell according to at least claim 1, wherein the second contact collecting the majority charge carriers is a metal contact (28) applied directly on the semiconductor substrate (16) and/or a metal contact (60, 82, 108) applied to a highly doped semiconductor substrate.

6. Solar cell according to at least one of the preceding claims, wherein at least a first passivation layer (66, 96, 114) extends along the back surface of the semiconductor substrate (16).

7. Solar cell according to at least one of the preceding claims, wherein the back surface of the semiconductor substrate (16) has a minority charge carrier on the minority charge carrier layer (emitter layer) (94, 122) conducting these collecting first contacts (58, 80, 106) that is separated with regard to potential from the contacts (60, 82, 108) conducting the (second) contacts collecting majority charge carriers.

8. Solar cell according to at least one of the preceding claims, wherein the emitter layer (94, 122) is formed in the surface region of the semiconductor substrate and/or is influenced by charges in the first passivation layer (96, 114) applied directly on the semiconductor structure.

9. Solar cell according to at least one of the preceding claims, wherein the semiconductor substrate (16) is a p-type doped semiconductor and the emitter layer (94, 122) is a highly doped n-type layer (n⁺) and/or an n-type conducting inversion layer or a hetero-transition formed by positive charges in the first passivation layer (96, 114).

10. Solar cell according to at least one of the preceding claims, wherein the first and/or second contact (80, 82) are arranged regionally on the segment of the first or second longitudinal flank (74, 76), directly on the latter or on an insulator layer (88), previously covered with passivation material and then exposed from it.

11. Solar cell according to at least one of the preceding claims, wherein the first and/or second contacts (26, 28;

58, 60;

80, 82;

106, 108;

132) run linearly in the longitudinal direction for the first or second longitudinal flanks (20, 22, 62, 64, 74, 76, 110, 112) and on these.

12. Solar cell according to at least one of the preceding claims, wherein the first and/or second contact (26, 28;

58, 60;

80, 82;

106, 108;

132) preferably run in the upper longitudinal rim side half of the first or second longitudinal flank (20, 22, 62, 64, 74, 76, 110, 112).

13. Solar cell according to at least one of the preceding claims, wherein at least the first or second longitudinal flank (138) having the first and/or the second contact has a texture (144).

14. Solar cell according to at least one of the preceding claims, wherein the texture is formed by pyramid-like projections (144).

15. Solar cell according to at least one of the preceding claims, wherein the linear or strip-like elevation (78, 104, 130, 140) having the first and second longitudinal flank (74, 76, 110, 112) has a breadth B in its semiconductor substrate side base (55) which is smaller or equals double the diffusion length of the minority charge carrier in the semiconductor substrate (16).

16. Solar cell according to at least one of the preceding claims, wherein the first and second contacts (80, 82;

106, 108;

132) proceeding from an elevation (78, 104, 130, 140) with its respective elevation base side longitudinal edges span a first plane, and wherein a sectional plane (57) intersecting with the longitudinal flanks (62, 64) running parallel to the plane spanned by the semiconductor substrate has a breadth B that is smaller than or equal to double the diffusion length of the minority charge carrier in the semiconductor substrate between the first plane and the semiconductor layer side base (55) of the elevation.

17. Solar cell according to at least one of the preceding claims, wherein the spacing between the base center of the elevation (78, 104, 130, 140) on the rim running on the base side of the second contact (82, 108) is greater than half the breadth of the basis (55).

18. Solar cell according to at least one of the preceding claims, wherein the breadth B of the base (55) of the elevation (56) or the sectional plane (57) comes to 5 μ

m≦

B≦

2 mm.

19. Solar cell according to at least one of the preceding claims, wherein the semiconductor substrate (16) has a thickness D with 20 μ

m≦

D≦

300 μ

m outside the elevation.

20. Solar cell according to at least one of the preceding claims, wherein the solar cell (10) is structured on the front side by parallel-running trenches that for their part run perpendicular to the elevations (18, 50, 52, 54, 56, 78, 104, 130, 140) on the back (14) of the solar cell.

21. Solar cell according to at least one of the preceding claims, wherein the front surface of the solar cell (10) has a passivation layer and/or anti-reflection layer.

22. Solar cell according to at least one of the preceding claims, wherein the passivation layer is the antireflection layer.

23. Solar cell according to at least one of the preceding claims, wherein the passivation layer (172) or the anti-reflection layer consists of plasma silicon nitride.

24. Solar cell according to at least one of the preceding claims, wherein the first and/or second contacts (26, 28, 58, 60, 80, 82, 106, 108, 132) running parallel to one another are connected through a collection contact such as a metal band respectively running perpendicular or basically perpendicular to this.

25. Solar cell according to at least one of the preceding claims, wherein the collector contact is connected with the respective first or second contacts, especially through a conductive adhesive.

26. Solar cell according to at least one of the preceding claims, wherein the semiconductor material is monocrystalline, polycrystalline or amorphous or is an element or semiconductor material.

27. Solar cell according to at least one of the preceding claims, wherein the passivation layer consists of or contains SiO₂, SiN, Al₂O₃, a-Si, a-Si:

H.

28. Solar cell according to at least one of the preceding claims, wherein the passivation layer consists of a double or multiple layer with a-Si or a-Si:

H running on the substrate side over which at least one layer, preferably of SiN, SiO₂, is arranged.

29. Solar cell according to at least one of the preceding claims, wherein the emitter layer (94, 122) runs spaced in relation to the second contact (82, 108).

30. Solar cell according to at least one of the preceding claims, wherein the passivation layer indirectly or directly prevents a charge carrier transport between first and second contact or basically prevents it.

31. Solar cell in the form of a thin layer solar cell in which the first and second minority or majority charge carrier-collecting contacts are arranged on the front surface of the semiconductor substrate constructed and/or arranged according to at least one of the preceding claims.

32. Method for manufacturing a solar cell according to at least one of the preceding claims, including a semiconductor substrate with front and back side in which minority and majority charge carriers are generated through incident radiation energy, which are collected and discharged by first and second contacts running over back surfaces having elevations delimiting first trenches having strip or bar-like first and second longitudinal flanks, whereby the first and/or second electrical contacts are applied directly on the back surface or are applied following whole are or largely whole area covering of the back surface with a passivation layer and if need be removal of regions of the passivation layer and on regions of the semiconductor substrate thus exposed, wherein the first trenches of the back are constructed with trench bottoms and elevations of the back with outer segments which run parallel to the plane spanned by the semiconductor substrate, wherein on at least some of the elevations, the first electrical contacts are applied on the first longitudinal flanks of the elevations and the second electrical contacts on the second longitudinal flanks of the elevations such that the first and second electrical contacts are spaced from one another on the trench bottom side as well as on the outer segment side.

33. Method according to claim 32, wherein the first and/or second contact is applied by evaporation deposition of material under an angle α

a in relation to the normal proceeding from the plane spanned by the semiconductor substrate, whereby the angle of evaporation deposition α

comes to α

≠

0° and

α

≠

90°

.

34. Method according to claim 32 or 33, wherein ions are implanted free of masking for doping the first and/or second longitudinal flank, especially beneath the first and/or second contact to be constructed on this such that these arise under an angle of incidence β

toward the normal, whereby the angle of incidence β

comes to β

≠

0°

, β

≠

90°

.

35. Method according to at least one of claims 32 to 34, wherein a highly doper layer is formed in the semiconductor substrate in particular by local heating by, for example, laser irradiation and/or light irradiation of the first and/or second longitudinal flange, whereby in particular areal extension of the highly doped layer is equal or greater than the areal extension of the first and/or second contact on the semiconductor substrate, whereby the first and/or second flank are irradiated especially when using shadowing brought about by the elevations.

36. Method according to at least one of claims 32 to 35, wherein the first contacts are constructed in a first oblique evaporation deposition step and then the second contacts are constructed in a second evaporation deposition step or the reverse.

37. Method according to at least one of claims 32 to 36, wherein the back surface of the semiconductor substrate is covered over the whole surface or basically over the entire surface with a passivation layer and then, preferably through chemical-mechanical polishing, at least the passivation material and if need be semiconductor material are worn away in the free longitudinal rim region of the elevations as well as especially [in] the plateau-like region running between the longitudinal regions to form the outer segment.

38. Method according to at least one of claims 32 to 37, wherein the first and/or second contact if need be runs regionally on the elevation side of the passivation layer.

39. Method according to at least one of claims 32 to 38, wherein the back surface of the semiconductor substrate is covered with a further passivation layer or a passivation layer system preventing a short circuit after if need be necessary electrical separation of the first and second contacts proceeding from a common elevation.

40. Method according to at least one of claims 32 to 39, wherein tunnel oxide layers for the first contacts to be constructed as MIS contacts are formed during tempering by oxygen administration in the region of the first longitudinal flanks of the elevations.

41. Method according to at least one of claims 32 to 40, wherein regional removal of the first passivation layer or of the metal present [in] segments of elevations extending along the first and second longitudinal flanks [takes place] in particular through chemical-mechanical polishing such that the elevations are oriented in the direction of motion of a polishing element with a translatory or rotary motion such that these run parallel to each other or under an angle β

with 1°

C.≦

β

≠

30°

C.

42. Method according to at least one of claims 32 to 41, wherein a local back field is formed, for example by boron implantation, boron diffusion or alloying with aluminum, for example preferably prior to applying the metal to construct the second contact in the region of the latter.

43. Method according to at least one of claims 32 to 42, wherein a layer (emitter layer) discharging minority charge carriers is formed under the first passivation layer, preferably by diffusion by doping atoms such as phosphorus.

44. Method according to at least one of claims 32 to 43, wherein the emitter layer is formed by increasing the positive charge density, especially by incorporating alkaline metal-containing substances in the first passivation layer, such as a silicon nitride layer, whereby the increase of the charge density preferably lies at a distance d with 1 nm<

d<

10 nm from the semiconductor surface.

45. Method according to at least one of claims 32 to 44, wherein regions of longitudinal flanks are shadowed perpendicular or almost perpendicular to their longitudinal extension prior to constructing the first and/or second contacts, and an additional contact electrically conductively connecting the first or second electrical contacts is applied on such a shadowed region.

3. Solar cell according to claim I or 2, wherein the semiconductor substrate (16) is highly doped by, for example, diffusion, ion implantation or alloying and/or is inverted and/or has a hetero-transition at least in its surface running under the first and/or the second contact (26, 28;

58, 60;

80, 82;

106, 108;

132).