Silicon solar cell and production method thereof

• US 20050133084A1
• Filed: 10/08/2004
• Published: 06/23/2005
• Est. Priority Date: 10/10/2003
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Joge, Toshio, Hosoya, Tomonori, Araki, Ichiro
• Granted Patent: US 7,495,167 B2
• Time in Patent Office: Days
• US Class Current: 136/255
• CPC Class Codes: H01L 31/03529 Shape of the potential jump barrier or surface barrier
• CPC Class Codes: H01L 31/068 the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

It is an object of the present invention to provide a silicon solar cell with n⁺pp⁺ BSF structure using solar grade silicon substrate, having a life time close to the initial level of the substrate. The solar cell of the present invention is produced by a back side boron diffusion step for diffusing boron on a back side of the substrate, a front side phosphorus diffusion step for diffusing phosphorus on a front side of the substrate, a low-temperature annealing step for annealing the substrate at 600° C. or lower for 1 hour or more, and an electrode firing step carried out at a peak temperature of 700° C. or lower for 1 minute or less, carried out in this order.

Claims

1. A production method of silicon solar cell having an n⁺pp⁺ structure with a phosphorus-diffused n⁺ layer and boron-diffused p⁺ layer formed on a p-type silicon substrate, comprising the steps of:

a back side boron diffusion step for diffusing-treating boron on a back side of the silicon substrate,

a front side phosphorus diffusion step for diffusing phosphorus on a front side of the silicon substrate after the back side boron diffusion step, and

a low-temperature annealing step for annealing the substrate at 600°

C. or lower for 1 hour or more after the front side phosphorus diffusion step.

2. A production method according to claim 1, further including the steps of:

an electrode printing step after the low-temperature annealing step; and

an electrode firing step after the electrode printing step,

wherein the electrode firing step is to fire the electrode at a peak temperature of 700°

C. or lower for a peak temperature period time of 1 minute or less.

3. A silicon solar cell having an n⁺pp⁺ structure with a phosphorus-diffused n⁺ layer formed on a first side of p-type silicon substrate and with a boron-diffused p⁺ layer formed on a second side of the silicon substrate, wherein

the n⁺pp⁺ structure of the silicon substrate is produced by the method according to claim 1 or 2,

each of the first and second sides is provided with a grid-shape electrode, and

each of the grid-shape electrodes is provided with a finger electrode and a busbar electrode.

4. A silicon solar cell according to claim 3 which is provided with a bifacial cell.

5. A silicon solar cell according to claim 3, wherein the grid-shape electrode formed on the first side is different in shape from the grid-shape electrode formed on the second side.

6. A silicon solar cell according to claim 3, wherein an area ratio of the grid-shape electrode formed on the first side to the first side is smaller than an area ratio of the grid-shape electrode formed on the second side to the second side.

7. A silicon solar cell according to any one of claims 3 to 6, wherein the width of the finger electrode is narrower than 100 μ

m, the width of the busbar electrode is wider than 10 times of the width of the finger electrode, and the width of the finger electrode is made wider at a base portion at which the finger electrode and the busbar electrode are connected to each other.