Czts thin film solar cell and manufacturing method thereof

A method of production of a CZTS-based thin film solar cell comprising:

• forming a metal back surface electrode layer on a substrate;
• forming on the metal back surface electrode layer a metal precursor film which includes at least Cu, Zn, and Sn which is selected so that, when expressed by coordinates using a Cu/(Zn+Sn) ratio as the abscissa and a Zn/Sn ratio as the ordinate, a Cu—Zn—Sn composition ratio (atomic ratio) falls in a region connecting a point A (0.825, 1.108), a point B (1.004, 0.905), a point C (1.004, 1.108), a point E (0.75, 1.6), and a point D (0.65, 1.5);
• sulfurizing and/or selenizing the metal precursor film to form a p-type CZTS-based light absorption layer;
• forming on the p-type CZTS-based light absorption layer an n-type high resistance buffer layer of a zinc compound;
• and
• forming on the n-type high resistance buffer layer an n-type transparent conductive film,
• wherein when the metal precursor film has a Zn/Sn ratio over 1.11, after formation of the p-type CZTS-based light absorption layer and before formation of the n-type high resistance buffer layer, the method performs treatment to add Sn to the surface of the p-type CZTS-based light absorption layer on the n-type high resistance buffer layer side so as to form a region with a Zn/Sn ratio of 1.11 or less, then form the n-type transparent conductive film.