Heterojunction solar cell and preperation method thereof

A method for preparing a heterojunction solar cell, wherein the method comprises:

• providing a semiconductor substrate layer;
• and
• forming a back composite transparent conductive film on one side of the semiconductor substrate layer, wherein a process for forming the back composite transparent conductive film comprises:
• forming a first back transparent conductive film on one side of the semiconductor substrate layer, and
• forming a second back transparent conductive film on a surface of the side of the first back transparent conductive film facing away from the semiconductor substrate layer,
• wherein both the first back transparent conductive film and the second back transparent conductive film are doped with group III heavy atoms and a concentration of group III heavy atoms in the second back transparent conductive film is lower than that of the group III heavy atoms in the first back transparent conductive film,
• wherein the process for forming the back composite transparent conductive film further comprises forming a third back transparent conductive film on one side of the semiconductor substrate layer before forming a first back composite transparent conductive film,
• wherein the third back transparent conductive film is located between the first back transparent conductive film and the semiconductor substrate layer after forming the first back transparent conductive film,
• wherein a work function of the third back transparent conductive film is higher than that of the first back transparent conductive film and higher than that of the second back transparent conductive film,
• wherein a mobility of the third back transparent conductive film is greater than that of the first back transparent conductive film and greater than that of the second back transparent conductive film, and
• wherein a concentration of doping ions in the third back transparent conductive film is lower than that of group III heavy atoms in the first back transparent conductive film and lower than that of group III heavy atoms in the second back transparent conductive film.