Solar cell and solar cell manufacturing method

A solar cell comprising:

• an n-type silicon substrate;
• a p-type impurity diffusion layer formed on one side of the n-type silicon substrate and containing a p-type impurity element;
• an n-type impurity diffusion layer formed on an opposite side of the n-type silicon substrate and containing an n-type impurity element at a higher concentration than the n-type silicon substrate, the n-type impurity diffusion layer having a first n-type impurity diffusion layer in which an n-type impurity element is diffused at a first concentration, and a second n-type impurity diffusion layer in which an n-type impurity element is diffused at a second concentration lower than the first concentration;
• on-p-type-impurity-diffusion-layer electrodes formed on the p-type impurity diffusion layer;
• and
• on-n-type-impurity-diffusion-layer electrodes formed on the first n-type impurity diffusion layer, wherein
• a concentration of the n-type impurity element at a surface of the first n-type impurity diffusion layer is between 5×1020 atoms/cm3 and 2×1021 atoms/cm3 inclusive, and a concentration of the n-type impurity element at a surface of the second n-type impurity diffusion layer is between 5×1019 atoms/cm3 and 2×1020 atoms/cm3 inclusive.

A solar cell manufacturing method, comprising:

• a first step of forming a p-type impurity diffusion layer containing a p-type impurity element on one side of an n-type silicon substrate;
• a second step of applying an n-type dopant-containing paste containing an n-type impurity element to an opposite side of the n-type silicon substrate;
• a third step of subjecting the n-type silicon substrate to a first heat treatment under gas atmosphere not containing an n-type impurity element in a processing chamber to allow the n-type impurity element to be diffused from the n-type dopant-containing paste into a region of the n-type silicon substrate under the n-type dopant-containing paste to thereby form a first n-type impurity diffusion layer in the region of the n-type silicon substrate under the n-type dopant-containing paste, the first n-type impurity diffusion layer having the n-type impurity element diffused at a first concentration;
• a fourth step of subjecting the n-type silicon substrate to a second heat treatment under dopant-containing gas atmosphere containing an n-type impurity element in the processing chamber to allow the n-type impurity element to be diffused from the dopant-containing gas into unapplied regions having the n-type dopant-containing paste not applied thereon on the opposite side of the n-type silicon substrate to thereby form a second n-type impurity diffusion layer in the unapplied regions, the second n-type impurity diffusion layer having the n-type impurity element diffused at a second concentration lower than the first concentration;
• a fifth step of removing the n-type dopant-containing paste;
• a sixth step of forming on-p-type-impurity-diffusion-layer electrodes on the p-type impurity diffusion layer;
• and
• a seventh step of forming on-n-type-impurity-diffusion-layer electrodes on the first n-type impurity diffusion layer.