Quantum dot record

C&I Issue 3, 2020

An international team of researchers has set a world record for converting solar energy to electricity using quantum dot devices. They could be developed as flexible outer skins in next generation solar panels.

The team led by Lianzhou Wang of the University of Queensland, Australia, achieved a 16.6% efficiency for their quantum dot solar devices (Nature Energy, doi: 10.1038/s41560-019-0535-7); the previous record was 13.4%. The US National Renewable Energy Laboratory recognised the achievement after independent testing.

‘This near 25% improvement in efficiency is important,’ says Wang. ‘It is effectively the difference between quantum dot solar cell technology being an exciting “prospect” and being commercially viable.’

Wang’s team worked with mixed caesium and formamidinium lead triiodide perovskite systems in the form of quantum dots. It is challenging to synthesise such complex systems with the right properties for high-performance solar cells because their surfaces tend to be rough and unstable.

They overcame these challenges by using oleic acid ligands to control the synthesis, which allowed the systems to form rapidly and with much fewer surface defects.

The team also demonstrated that the quantum dot devices were substantially more stable in sunlight, compared with their thin-film counterparts. They retained 94% of the original power conversion efficiency under continuous illumination for 600 hours.

The new material offers several advantages over conventional solar technologies, which tend to use rigid, costly materials, says Wang. ‘This new generation of [flexible] quantum dots is compatible with more affordable and large-scale printable technologies,’ he says, opening up a range of potential applications, such as a transparent skin to powering cars, planes and homes, as well as wearable technology.

The near 25% improvement in efficiency over the previous world record could be a milestone, agrees Jingbi You of the Institute of Semiconductors, Chinese Academy of Sciences in Beijing. ‘This is a significant gain considering the various uses for these cells when converted into thin, flexible films that can be pasted on a number of surfaces to generate electricity. Eventually it could serve as one of the major parts in meeting the UN’s goal to increase the share of renewable energy in the global energy mix.

Unlike previous studies, You notes that Wang’s team found that increasing the concentration of oleic acid ligands during the formation of mixed-cation perovskite quantum dots helps preserve high radiative efficiency by suppressing surface defects.

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