HyET Solar has developed proprietary production technology for producing lightweight and flexible thin-film silicon solar cells on long foil substrates in a number of roll-to-roll steps. The active layers which convert light into electricity are less than 0.003 millimeters thick. First, solar cells based on single junction amorphous silicon solar cells (~7% efficiency) were developed. HyET Solar has now added the technology for flexible solar foil with amorphous nanocrystalline silicon tandem cells for product efficiencies exceeding 10%.
A unique feature of the process is the use of a temporary (aluminum) foil. The advantage of using a temporary foil is that it enables cost-efficient, homogeneous, roll-to-roll deposition of the active thin-film solar cell layers. This applies in particular to the first layer, which is the transparent top contact. This layer is deposited by means of atmospheric pressure CVD at 500º C, conditions which require high-temperature resistant aluminum foil. The resulting TCO layer has an excellent performance and is essential for optimal energy efficiency and durability. Onto this TCO layer the silicon and the metallic back contact are deposited.
The solar cell layers are divided in longitudinal cells by laser patterning. Such monolithic interconnection allows for far-reaching process automation, customization of the final product and optimal energy yield of the solar foil in the application. The foil is laminated on a permanent carrier foil: a non-exotic polymer foil can be used since no high-temperature steps are involved from this stage on.
Finally, the temporary (aluminum) foil is removed from the active cell area, while at the edges it is retained for current collecting bus bars. These strips guide the generated solar electricity via connection points and standard cables. To protect the thin solar cells, they are embedded in a durable, proprietary encapsulation package.