Three dimensional amorphous silicon/microcrystalline silicon solar cells

• US 5,538,564 A
• Filed: 03/18/1994
• Issued: 07/23/1996
• Est. Priority Date: 03/18/1994
• Status: Expired due to Term

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Kaschmitter, James L.
• Primary Examiner(s): Weisstuch, Aaron
• Application Number:
  US08/214,750
• Time in Patent Office: 858 Days
• Field of Search: 136/255, 136/256, 136/258 AM, 136/258 PC, 257/458, 257/465, 437/2-5, 437/19, 437/166, 437/168, 437/173
• US Class Current: 136/255
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact solar cells
• CPC Class Codes: H01L 31/03529 Shape of the potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/03685 including microcrystalline silicon, uc-Si
• CPC Class Codes: H01L 31/03921 including only elements of Group IV of the Periodic Table
• CPC Class Codes: Y02E 10/545 Microcrystalline silicon PV cells
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02E 10/548 Amorphous silicon PV cells

Abstract

Three dimensional deep contact amorphous silicon/microcrystalline silicon (a-Si/μc-Si) solar cells which use deep (high aspect ratio) p and n contacts to create high electric fields within the carrier collection volume material of the cell. The deep contacts are fabricated using repetitive pulsed laser doping so as to create the high aspect p and n contacts. By the provision of the deep contacts which penetrate the electric field deep into the material where the high strength of the field can collect many of the carriers, thereby resulting in a high efficiency solar cell.

Claims

1. In a process for fabricating solar cells, the improvement comprising:

forming high aspect ratio contacts in a carrier collection material by repetitive pulsed laser doping to create p and n contacts having a depth substantially greater than the width thereof, resulting in very high current collection, thus providing an efficient solar cell.

2. The improvement of claim 1, additionally including forming the carrier collection material from the group consisting of amorphous silicon, amorphous silicon containing microcrystalline silicon formed by laser processing, and a graduation of amorphous silicon to microcrystalline silicon adjacent the contacts.

3. The improvement of claim 1, wherein the repetitive pulsed laser doping is carried out using a laser selected from the group of excimer, flashlamp, dye, and YAG lasers.

4. The improvement of claim 1, wherein the p and n contacts are formed by repetitive pulsed laser doping carried out in a gaseous dopant environment or on predeposited dopant materials.

5. The improvement of claim 1, wherein the repetitive pulsed laser doping for forming the p contacts is carried out in an environment of a dopant selected from the group consisting of BF₃, B₂ H₆, and other p-type gaseous dopant environments.

6. The improvement of claim 1, wherein the repetitive pulsed laser doping for forming the n contacts is carried out in an environment of a dopant selected from the group consisting of PF₅, AsF₅, AsH₄, PH₃, and other n-type gaseous dopant environments.

7. The improvement of claim 1, wherein the repetitive pulsed laser doping is carried out with a pulse length of 5 to 60 ns, energy level of about 150 to 800 mJcm^-2, and pulse spacing of about 5 seconds.

8. The improvement of claim 1, additionally including forming the carrier collection material from the group consisting of a-Si:

H/μ

c-Si;

H, pc-Si, and c-Si.

9. The improvement of claim 1, additionally including forming layers of material on opposite sides of the carrier collection material from the group consisting of SiO₂, TiO₂, TaO₂, Al₂ O₃, and MgO.

10. In a solar cell having a carrier collection material, the improvement comprising:

said carrier collection material containing only a plurality of high aspect ratio p and n contacts therein;

said plurality of high aspect ratio p and n contacts having a depth substantially greater than the width thereof which penetrate the electric field at least half-way into the carrier collection material where the high strength of the electric field can collect the carriers,

said p and n contacts being composed of doped carrier collection material.

11. The improvement of claim 10, wherein the plurality of high aspect ratio p and n contacts are formed in the carrier collection material by repetitive pulse laser doping of areas in the carrier collection material.

12. The improvement of claim 11, wherein the carrier collection material is selected from the group composed of amorphous silicon, laser processed amorphous silicon containing microcrystalline silicon, and a graduation of amorphous silicon to microcrystalline silicon around the contacts.

13. The improvement of claim 12, additionally including a plurality of layers of silicon dioxide, at least one layer thereof being on opposite sides of said carrier collection material.

14. The improvement of claim 13, additionally including a plurality of electrical connectors extending through one of said silicon dioxide layers and in contact with said p and n contacts.

15. The improvement of claim 14, wherein said electrical connectors are also in contact with bus bars located on an outer surface of said one of said silicon dioxide layers.

16. The improvement of claim 15, additionally including a layer of ultra-violet transparent material located on an outer surface of another of said layers of silicon dioxide and adapted to be positioned to receive solar radiation.

17. The improvement of claim 16, wherein said layer of transparent material is formed from the group consisting of E-CTFE, PVDF, E-TFE, PES, PTFE, FEP, HDPE, and other low-temperature polymeric materials which are incapable of withstanding temperatures of over about 180°

C. for a sustained time period longer than about 10⁵ ns.

18. The improvement of claim 10, wherein said carrier collection material is selected from the group consisting of a-Si:

H/μ

c-Si;

H, pc-Si, and c-Si.

19. The improvement of claim 10, additionally including a layer of material selected from the group consisting of SiO₂, TiO₂, TaO₂, Al₂ O₃, and MgO on opposite sides of the carrier collection material.

20. A process for fabricating three dimensional deep contact a-Si/μ

c-Si solar cells, comprising;

depositing a layer of a transparent thermal barrier material on a uv radiation transparent substrate;

depositing a layer of active material on the transparent thermal barrier material;

forming by pulsed energy processing a plurality of doped high aspect ratio contacts in said active material which extend deep into said active material;

depositing a layer of protective material on the layer of active material;

forming doped electrical connectors in said layer of protective material which align with the contacts formed in the active material; and

providing a conductive grid means in contact with said doped electrical connectors.

21. The process of claim 20, additionally including forming the substrate from material selected from the group of E-CTFE, PVDF, E-TFE, PES, PTFE, FEP, and HDPE.

22. The process of claim 21, wherein at least one of the layers of thermal barrier material and protective material is composed of SiO₂.

23. The process of claim 22, wherein said layer of active material is composed of a-Si:

H/μ

-Si;

H.

24. The process of claim 23, wherein said plurality of doped high aspect ratio contacts comprise at least one p and one n contacts.

25. The process of claim 24, wherein said doped contacts are formed by repetitive pulsed laser processing and extend at least half-way into said layer of active material.

26. The process of claim 20, wherein at least one of the layers of thermal barrier material and protective material is composed of at least one of the group consisting of SiO₂, TiO₂, TaO₂, Al₂ O₃, and MgO.