Multi-junction photovoltaic device and fabrication method

A photovoltaic device comprising:

• a back contact structure on an upper surface of a flexible substrate;
• a first solar cell present on the back contact structure, wherein the first solar cell includes a germanium-containing crystalline semiconductor layer having a thickness ranging from 100 nm to 100 μm, wherein the first solar cell absorbs a first range of wavelengths;
• at least a second solar cell present on the first solar cell, the at least one second solar cell is composed of at least one semiconductor material that is selected so that the second solar cell absorbs a second range of wavelengths that is different than the first range of wavelengths absorbed by the first solar cell;
• and
• a front contact structure on the upper surface of the at least one second solar cell, wherein the germanium-containing crystalline semiconductor layer of said first solar cell has a first conductivity type, and the first solar cell further comprises an intrinsic semiconductor layer that is in direct contact with the germanium containing crystalline semiconductor layer, and an upper semiconductor layer having a second conductivity type that is opposite the first conductivity type that is in direct contact with the intrinsic semiconductor layer.

A photovoltaic device comprising:

• a back contact structure on an upper surface of a flexible substrate;
• a first solar cell present on the back contact structure, wherein the first solar cell includes a germanium-containing crystalline semiconductor layer having a thickness ranging from 100 nm to 100 μm, wherein the first solar cell absorbs a first range of wavelengths;
• at least a second solar cell present on the first solar cell, the at least one second solar cell may be composed of at least one semiconductor material that is selected so that the second solar cell absorbs a second range of wavelengths that is different than the first range of wavelengths absorbed by the first solar cell;
• and
• a front contact structure on the upper surface of the at least one second solar cell, wherein said at least one second solar cell present on the first solar cell is selected from the group consisting of:
• (a) a p-i-n junction of hydrogenated amorphous silicon, hydrogenated amorphous silicon carbide, hydrogenated amorphous silicon-germanium, hydrogenated crystalline silicon, or a combination thereof;
• (b) a first p-i-n junction of hydrogenated amorphous silicon germanium present on the first solar cell, and a second p-i-n junction of hydrogenated amorphous silicon which may contain carbon present on the first solar cell;
• (c) a first p-i-n junction of hydrogenated crystalline silicon on the first solar cell, a second p-i-n junction of hydrogenated amorphous silicon germanium present on the first solar cell, and a third p-i-n junction of hydrogenated amorphous silicon comprising carbon present on the second solar cell;
• (d) a first p-i-n junction of hydrogenated amorphous silicon germanium present on the first solar cell, a second p-i-n junction of hydrogenated amorphous silicon comprising carbon present on the first solar cell, and a third junction of hydrogenated amorphous silicon-carbide on the second solar cell;
• (e) a first p-i-n junction of hydrogenated nano/microcrystalline silicon present on the first solar cell, a second p-i-n junction of hydrogenated amorphous silicon comprising carbon present on the first solar cell, and a third junction of hydrogenated amorphous silicon-carbide on the second solar cell;
• and
• (f) a p-type buffer region on the first solar cell, a layer of copper-indium-gallium sellenide, cadmium telluride, CZTS (copper, zinc, tin, and sulfur) or CZTSe (copper, zinc, tin, selenium) on the p-type buffer region, and an n-type cadmium sulfide.