Method and apparatus for self-doping negative and positive electrodes for silicon solar cells and other devices

• US 6,180,869 B1
• Filed: 05/04/1998
• Issued: 01/30/2001
• Est. Priority Date: 05/06/1997
• Status: Expired due to Term

• Current Assignee: Suniva, Inc.
• Original Assignee: Ebara Solar, Inc.
• Inventors: Meier, Daniel L., Davis, Hubert P.
• Primary Examiner(s): Robinson, Ellis
• Assistant Examiner(s): MIGGINS, MICHAEL C
• Application Number:
  US09/072,411
• Time in Patent Office: 1,002 Days
• Field of Search: 136/256, 136/261, 136/262, 257/461
• US Class Current: 136/256
• CPC Class Codes: H01L 21/28512 on semiconductor bodies comprising elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact solar cells
• CPC Class Codes: H01L 31/0288 characterised by the doping material
• 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 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A self-doping electrode to silicon is formed primarily from a metal (major component) which forms a eutectic with silicon. A p-type dopant (for a positive electrode) or an n-type dopant (for a negative electrode) is alloyed with the major component. The alloy of major component and dopant is applied to a silicon substrate. Once applied, the alloy and substrate are heated to a temperature above the major component-silicon eutectic temperature such that the major component liquefies more than a eutectic proportion of the silicon substrate. The temperature is then decreased towards the eutectic temperature permitting molten silicon to reform through liquid-phase epitaxy and while so doing incorporate dopant atoms into its regrown lattice. Once the temperature drops below the major component-silicon eutectic temperature the silicon, which has not already regrown into the lattice, forms a solid-phase alloy with the major component and the remaining unused dopant. This alloy of major component, silicon and unused dopant is the final contact material. Alternatively, a self-doping electrode may be formed from an unalloyed metal applied to a silicon substrate. The metal and substrate are heated to a temperature above the metal-silicon eutectic temperature in an ambient gas into which a source of vaporized dopant atoms has been introduced. Dopant atoms in the ambient gas are absorbed by the molten mixture of metal-silicon to a much greater extent than they are absorbed by the solid silicon substrate surfaces. The temperature is then decreased to below the metal-silicon eutectic temperature. During this temperature decrease, the doped regrown silicon layer and the metal-silicon alloy final contact material are created in the same process as described above.

Claims

1. A solar cell, comprising:

a rectifying junction, at least partially exposable to solar radiation for generation of electrical current, made of a first semiconductive material, comprising a first half and a second half;

a first electrode making ohmic contact to the first half;

a second electrode making ohmic contact to the second half;

wherein the first half has been doped with a first dopant to be a semiconductive material of a first type;

wherein the second half has been doped with a second dopant to be a semiconductive material of a second type opposite to the first type;

wherein the second half comprises a first region beneath the second electrode that has been more heavily doped with a third dopant than at least a portion of the remaining second half;

wherein the first region is aligned with the second electrode;

wherein the second electrode comprises an alloy of a first metal, the third dopant and the first semiconductive material;

wherein the first metal is capable of forming a eutectic with the first semiconductive material and the first metal is not capable of significantly doping the first semiconductive material; and

wherein that part of the second electrode that comprises the first metal and the first semiconductor comprises eutectic proportions of the first metal and the first semiconductive material.

2. The solar cell of claim 1, wherein the first metal of the second electrode is in proportion to a total of the third dopant of the second electrode and the third dopant of the first region, such that an alloy comprising the proportion of the first metal to the total of the third dopant is capable of existing as a solid, of single uniform phase, in a first temperature range, and transitions directly to a liquid phase at a second temperature range, wherein the second temperature range is immediately above the first temperature range.

3. The solar cell of claim 1, wherein the first dopant is antimony.

4. The solar cell of claim 1, wherein the first dopant is gallium.

5. The solar cell of claim 1, wherein the first dopant is phosphorous.

6. The solar cell of claim 1, wherein the first dopant is a Periodic Table Group III element.

7. The solar cell of claim 1, wherein the first dopant is a Periodic Table Group V element.

8. The solar cell of claim 1, wherein the third dopant is selected from the group consisting of a Periodic Table Group III element.

9. The solar cell of claim 1, wherein the third dopant is selected from the group consisting of a Periodic Table Group V element.

10. The solar cell of claim 1, wherein the first metal is silver.