Scientists from North Carolina State University have developed a new superabsorbing design that could substantially improve the light-absorption efficiency of thin film solar cells, as well as reduce their manufacturing costs. They demonstrated a reduction in the thickness of semiconductor materials used in the solar cells by over one order of magnitude without compromising the capability of solar light absorption, a breakthrough that could fundamentally solve their light-absorption efficiency problems, since the cells would need less material and the thin films could be deposited more quickly.
Enhancing solar light absorption is crucial in the development of high-efficiency, cost-effective solar cells. The team has been working on the fundamental issue of the maximum enhancement attainable in the semiconductor materials, as existing theory fails to address this problem due to the complicated optical properties of semiconductor materials. This prompted them to develop a new theoretical model and then leverage the model to show the upper limit of solar absorption enhancement for the active materials in solar cells.
The research, reported in Scientific Reports [Yu, et al., Sci. Rep. (2014), doi:10.1038/srep04107], initially investigated the maximum light absorption efficiency of semiconductor materials using light-trapping techniques, showing that to maximize solar absorption it requires a design where the light-trapping efficiency for solar light is equal to the intrinsic absorption efficiency of the semiconductor materials. They therefore designed a structure that could match their light-trapping efficiency with the absorption efficiency of the semiconductor materials. As senior author Linyou Cao said, “The structure should be very easy to produce with standard thin film deposition and nanolithography techniques.”
The latest thin film solar cells use an amorphous silicon layer of about 100 nm thick to capture most of the available solar energy. The structure proposed here – which in cross-section resembles a rectangular onion, with the light-absorbing semiconductor material coating a rectangular core and the semiconductor being coated with three layers of anti-reflective coating – can absorb 90% of available solar energy from only a 10 nm thick layer of amorphous silicon. The findings work for other materials; for instance, for a cadmium telluride layer of 1 μm thickness to absorb solar energy, the new design only requires a 50 nm thick layer of cadmium telluride to achieve the same results.
The next step is for the team to combine with industry partners to potentially help implement the design in the production of a new generation of solar cells.