System and method for tin plating metal electrodes

• US 9,496,429 B1
• Filed: 12/30/2015
• Issued: 11/15/2016
• Est. Priority Date: 12/30/2015
• Status: Active Grant

• Current Assignee: SolarCity Corporation (Tesla Inc.)
• Original Assignee: SolarCity Corporation (Tesla Inc.)
• Inventors: Erben, Christoph G., Sun, Zhi-Wen
• Primary Examiner(s): Blum, David S
• Application Number:
  US14/985,238
• Time in Patent Office: 321 Days
• Field of Search: 438/98
• US Class Current: 1/1
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/022433 Particular geometry of the grid contacts
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact solar cells
• CPC Class Codes: H01L 31/0682 back-junction, i.e. rearside emitter, solar cells, e.g. interdigitated base-emitter regions back-junction cells
• CPC Class Codes: H01L 31/1864 Annealing
• CPC Class Codes: H01L 31/1884 Manufacture of transparent electrodes, e.g. TCO, ITO
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

Systems and methods for fabricating a photovoltaic structure are provided. During fabrication, a patterned mask is formed on a first surface of a multilayer body of the photovoltaic structure, with openings of the mask corresponding to grid line locations of a first grid. Subsequently, a core layer of the first grid is deposited in the openings of the patterned mask, and a protective layer is deposited on an exposed surface of the core layer. The patterned mask is then removed to expose the sidewalls of the core layer. Heat is applied to the protective layer such that the protective layer reflows to cover both the exposed surface and sidewalls of the core layer.

Claims

1. A method for fabricating a photovoltaic structure by forming a first grid on a first surface of a multilayer body of the photovoltaic structure, the method comprising:

forming a patterned mask on the first surface of the multilayer body, wherein openings of the patterned mask correspond to grid line locations of the first grid;

depositing, using a plating technique, a core layer of the first grid in the openings of the patterned mask;

depositing, using a plating technique, a protective layer on an exposed surface of the core layer while the patterned mask is covering sidewalls of the core layer;

removing the patterned mask to expose the sidewalls of the core layer; and

applying heat to the protective layer such that the protective layer reflows to cover both the exposed surface and sidewalls of the core layer.

2. The method of claim 1, wherein the patterned mask includes a photoresist mask or a SiO₂ mask.

3. The method of claim 1, wherein the core layer includes a metallic layer comprising Cu.

4. The method of claim 1, wherein a thickness of the core layer is be between 10 and 100 microns.

5. The method of claim 1, wherein the protective layer includes one or more metallic materials selected from a group consisting of:

tin;

tin-lead alloy;

tin-zinc alloy;

tin-bismuth alloy;

tin-indium alloy;

tin-silver-copper alloy;

tin-lead-zinc alloy; and

tin-lead-copper alloy.

6. The method of claim 5, wherein the protective layer includes one or more of:

tin; and

tin-lead alloy.

7. The method of claim 1, wherein a thickness of the protective layer, before the protective layer reflows, is between 0.3 and 10 microns.

8. The method of claim 1, wherein a thickness of the protective layer, after the protective layer reflows, is between 0.1 and 5 microns.

9. The method of claim 1, wherein the multilayer body comprises at least:

a base layer;

an emitter layer positioned on a first side of the base layer; and

a surface field layer positioned on a second side of the base layer.

10. The method of claim 9, wherein the multilayer body further comprises:

a passivation layer positioned between the base layer and the emitter layer;

a second passivation layer positioned between the base layer and the surface field layer;

a transparent conductive oxide layer positioned on the emitter layer; and

a second transparent conductive oxide layer positioned on the surface field layer.

11. The method of claim 1, further comprising:

forming a second grid on a second surface of the multilayer body simultaneously with the first grid.