Back structure of solar cell, and solar cell with back structure

A back structure of a solar cell, comprising an aluminum oxide film layer disposed on a silicon wafer substrate of the solar cell, and a first silicon nitride film layer and a first silicon oxynitride film layer, which are successively disposed on the aluminum oxide film layer from inside to outside, wherein a refractive index of the first silicon nitride film layer is greater than a refractive index of the first silicon oxynitride film layer;

• further comprising a second silicon nitride film layer disposed on the first silicon oxynitride film layer, wherein the refractive index of the first silicon nitride film layer is greater than a refractive index of the second silicon nitride film layer, and a refractive index of the second silicon nitride film layer is greater than the refractive index of the first silicon oxynitride film layer;
• further comprising a second silicon oxynitride film layer disposed on the second silicon nitride film layer;
• further comprising a silicon oxide film layer disposed on the second silicon oxynitride film layer;
• wherein the second silicon nitride film layer comprises at least one sub silicon nitride film layer;
• the at least one sub silicon nitride film layer comprises a first sub silicon nitride film layer, a second sub silicon nitride film layer and a third sub silicon nitride film layer, which are successively disposed on the first silicon oxynitride film layer from inside to outside;
• a refractive index of the first sub silicon nitride film layer is 2.1-2.2, and a film thickness of the first sub silicon nitride film layer is 15-25 nm;
• a refractive index of the second sub silicon nitride film layer is 2.0-2.1, and a film thickness of the second sub silicon nitride film layer is 8-15 nm;
• a refractive index of the third sub silicon nitride film layer is 1.9-2.0, and a film thickness of the third sub silicon nitride film layer is 8-15 nm.