The National Nano Device Lab in Taiwan has developed a manufacturing process that can build integrated circuits combining a two-sided solar cell and thin-film transistors (TFTs). The underlying process is said to be environment-friendly and is billed as a step toward self-powered chips.
One side of the resulting chip features both a solar cell and TFTs made from CIGS (CuInGaSe2). These devices are on the back of a silicon-based solar cell. The chips are made without using environmentally harmful cadmium, or sodium, which is typically found in CIGS solar-cells. Cells often incorporate these materials to boost light conversion efficiency. To compensate, the CIGS layer was deposited on a textured surface, bringing the CIGS cell conversion efficiency up to 11%.
The TFTs set a record for CIGS technology, demonstrating a hole mobility of 0.22 cm2/V. The relatively low-temperature (400 to 500°C) and sodium-free manufacturing process used could make the CIGS fabrication technique compatible with CMOS processing.
The researchers will describe their work at the upcoming IEEE International Electron Devices Meeting (IEDM) in Washington, D. C., in December (“Bifacial CIGS [11% Efficiency]/Si Solar Cells By Cd-Free And Sodium-Free Green Process Integrated With CIGS TFTs,”).