Ultra-thin new solar cell structure conversion efficiency close to 20%

Researchers from the Center for Nanoscience and Nanotechnology (C2N) collaborated with researchers at Fraunhofer ISE in Germany to obtain nearly 20% of the new solar cell structure by making a 205nm thick GaAs ultra-thin absorption layer on the nanostructured back mirror. High conversion efficiency.

To date, state-of-the-art solar cells with 20% efficiency require a semiconductor material layer (GaAs, CdTe or copper indium gallium selenide) at least 1 micron thick, or even a silicon material layer of 40 μm or more. The reduced thickness reduces the deposition time, thereby saving the use of rare materials such as tellurium or indium. However, thinning the absorbent will subsequently reduce the absorption and conversion efficiency of sunlight. The plane mirror on the back of the battery has a two-way absorption path, but it cannot absorb itself. The previous methods of capturing light have greatly restricted the performance of solar cells in terms of optical and electrical losses.

The researchers of the research group led by Stéphane Collin and Andrea Cattoni collaborated with Fraunhofer ISE to develop a 205nm-thick III- A new way of capturing light with Group V semiconductor gallium arsenide. The main purpose is to manufacture nano-structured back mirrors to generate multiple overlapping resonances in solar cells, namely Fabry-Perot and guided mode resonances. They limit light to stay in the absorber for a longer period of time. Despite the small amount of material, it can still achieve effective optical absorption. Due to the existence of countless resonances, absorption is enhanced in the large spectral range of the solar spectrum from visible to infrared. Controlling the manufacture of nano-scale back mirrors is a key aspect of this project. The team used nanoimprint lithography, which is an inexpensive, fast, and scalable technology for imprinting sol-gel-derived titanium dioxide films.

Can this ultra-thin solar cell further improve performance? Research results published in Nature Energy show that this architecture should achieve 25% efficiency in the short term. Even if it is still unclear what the limit of this technology is, the researchers are still confident that the thickness can be further reduced by at least two times without reducing efficiency. GaAs solar cells are subject to cost constraints and have certain limitations in commercial applications, so researchers have extended this technical concept to large photovoltaic devices made of CdTe, CIGS, or silicon materials.