Silicon solar cell and production method thereof
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.
1. A production method of 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 boron-diffused p + layer formed on a second side of said 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,
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,
providing grid-shape electrodes on both the first side and the second side of the p-type substrate, and
providing each of the grid-shape electrodes with a finger electrode and a busbar electrode,
wherein the width of the finger electrode is narrower than 100 μm, 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.
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 made by the production method according to claim 1 or 2 , having the n + pp + structure with the phosphorus-diffused n + layer formed on the first side of the p-type silicon substrate and with the boron-diffused p + layer formed on the second side of the silicon substrate.
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 production method according to claim 1 , wherein said annealing step is performed in an inert gas atmosphere.
8. A production method according to claim 1 , wherein said grid-shape electrodes provided on both the first side and the second side of the p-type substrate are fired at a peak firing temperature of 700° C. or lower.
9. A production method according to claim 8 , wherein the grid-shape electrodes on both the first and second sides are simultaneously fired.
10. A production method according to claim 1 , wherein a width of the finger electrode at the base portion is 0.3 to 2 times of the width of the busbar electrode.
11. A silicon solar cell made by the production method according to claim 10 .