Protective insulating layer and chemical mechanical polishing for polycrystalline thin film solar cells

A method for forming a photovoltaic device, comprising:

• depositing a conductive layer on a glass substrate;
• forming an absorber layer formed from a Cu—Zn—Sn containing chalcogenide material on the conductive layer wherein the Cu—Zn—Sn containing chalcogenide material is a compound with a kesterite structure of the formula:
• Cu2−xZn1+ySn(S1−zSez)4+q wherein 0≦x≦1;
• 0≦y≦1;
• 0≦z≦1;
• −1≦q≦1;
• conformally depositing a protection layer over the absorber layer to fill in between grains of the absorber layer by an atomic layer deposition process;
• planarizing the protection layer and the absorber layer by performing a chemical mechanical polishing process to remove unwanted secondary phase material from a surface of the absorber layer;
• forming a buffer layer on the absorber layer;
• forming a first transparent conductor layer on the buffer layer;
• and
• depositing a second transparent conductor layer on the first transparent conductor layer.