Multi-junction solar cells and methods and apparatuses for forming the same

A method of forming a thin film multi-junction solar cell over a substrate, comprising:

• forming a first photovoltaic junction on a substrate, comprising:
• forming a p-type amorphous silicon layer;
• forming an intrinsic type amorphous silicon layer over the p-type amorphous silicon layer, wherein the intrinsic type amorphous silicon layer includes a p-i buffer intrinsic type amorphous silicon layer and a bulk intrinsic type amorphous silicon layer;
• and
• forming a n-type microcrystalline silicon layer over the intrinsic type amorphous silicon layer;
• and
• forming a second photovoltaic junction over the first photovoltaic junction, comprising:
• forming a p-type microcrystalline silicon layer;
• forming an intrinsic type microcrystalline silicon layer over the p-type microcrystalline silicon layer;
• and
• forming an n-type amorphous silicon layer over the intrinsic type microcrystalline layer.

A tandem junction photovoltaic device, comprising:

• a first photovoltaic junction and a second photovoltaic junction, wherein the first photovoltaic junction comprises:
• a p-type amorphous silicon layer;
• a p-i buffer intrinsic type amorphous silicon layer;
• a bulk intrinsic type amorphous silicon layer;
• and
• a n-type microcrystalline silicon layer;
• and wherein the second photovoltaic junction comprises:
• a p-doped microcrystalline silicon layer;
• an intrinsic type microcrystalline silicon layer;
• and
• a n-doped amorphous silicon layer adjacent to the intrinsic type microcrystalline silicon layer.

A tandem junction photovoltaic device, comprising:

• a first photovoltaic junction and a second photovoltaic junction, wherein the second photovoltaic junction comprises:
• a p-doped microcrystalline silicon layer;
• an intrinsic type microcrystalline silicon layer, wherein the intrinsic type microcrystalline silicon layer is formed by a multiple step deposition process, wherein each deposition step has a gas mixture having different hydrogen to silane ratio to form different film crystalline fraction in each deposition step;
• and
• an n-doped amorphous silicon layer adjacent to the intrinsic type microcrystalline silicon layer.