A team of researchers from the University of Illinois Urbana-Champaign and Arizona State University have achieved a tandem solar cell efficiency of 25% using gallium arsenide phosphide (GaAsP) and silicon (Si) solar cells, calling it III-V/Si epitaxial tandem solar cell.
Matching it with a Si backside texturing, the team obtained 25% efficiency with a closely matched Jsc of 18.8 mA/cm². For this the researchers improved the top cell carrier lifetime by reducing the defect density. This is attained by using a wide-band gap AlGaAsP electron-blocking layer that formed a pristine interface in the GaAsP cell. Then combining this improved top cell carrier collection ability with rear textured silicon enabled them to obtain the efficiency level. The work validates GaAsP as an efficient and stable partner for Si in tandem structures, according to the scientists.
Even though GaAsP and other semiconductor materials mirroring it are efficient, these are expensive hence can't be expected to be the sole material needed to make solar panels. Therefore, the team complemented it with low-cost silicon.
"Eventually, a utility company could use this technology to get 1.5 times more energy out of the same amount of land on its solar farms, or a consumer could use 1.5 times less space for rooftop panels," said University of Illinois Electrical and Computer Engineering Professor Minjoo Larry Lee.
Commercializing the technology may not be possible at this stage, but Lee believes energy providers and consumers will see the value in using stable materials to achieve a performance boost.
Supported by the National Science Foundation of US and National Aeronautics and Space Administration (NASA), the research work has been published in the journal Cell Reports Physical Science.
24.2% efficiency for all-perovskite tandem cell
Researchers from China's Nanjing University have claimed 24.2% certified efficiency for all-perovskite tandem solar cells on an area over 1 cm² using surface anchoring zwitterionic antioxidant. Their research published in Nature Energy journal adds that the team obtained in-lab power conversion efficiencies of 25.6% and 21.4% for 0.049 cm2 and 12 cm2 devices, respectively.
"The zwitterionic antioxidant inhibits Sn2+ oxidation and passivates defects at the grain surfaces in mixed lead–tin perovskite films, enabling an efficiency of 21.7% (certified 20.7%) for single-junction solar cells," the research work reads. "The encapsulated tandem devices retain 88% of their initial performance following 500 hours of operation at a device temperature of 54–60 °C under one-sun illumination in ambient conditions."