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Cheaper, safer, thin-film solar with Kesterite

Prof. Xiaojing Hao and her team have achieved two energy efficiency world records for a new solar cell material – sulfide kesterite, also known as CZTS.


Australia has the highest per capita uptake of rooftop solar in the world. This reflects a growing demand for cheap and renewable energy. However, there are many drawbacks to current silicon wafer-based solar technologies. They are expensive to produce and difficult to recycle. They are also inflexible and must be installed on a flat surface, severely limiting the locations in which they can be used.

One solution to this is flexible thin-film solar cells which can be installed as coatings on a range of surfaces, from car bodies to buildings. However, commercially available thin-film solar options, CIGS and CdTe, use scarce and toxic materials, making them expensive to produce and recycle. Cheaper, non-toxic, thin-film alternatives are needed in order to scale up their adoption.


Prof. Xaiojing Hao and her team at UNSW Sydney have broken four world records in their quest to create cheap and ‘green’ thin-film solar cells. In the process, Prof. Hao has emerged as a world leader in the area, recognised in both the 2020 Prime Minister’s and 2018 NSW Premier’s Prizes for Science.

Prof. Hao has been recognised for her pioneering work in thin-film photovoltaics.

Her team is developing an alternative to CIGS and CdTE called sulfide kesterite (Cu2ZnSnS4), also referred to as CZTS, that uses non-toxic and abundant elements. It can also be manufactured using existing equipment that is already in use to produce CIGS. Another benefit of CZTS is it captures a different spectrum of light than silicon solar cells. This means they can be combined into a ‘tandem’ solar cell that can capture more energy than silicon or CZTS alone.

Prof. Hao’s team have already achieved two energy efficiency world records for CZTS, breaking the 10% energy conversion efficiency barrier for this promising new material. To achieve this result the researchers used a range of high-end microscopy techniques across three of our NSW facilities: UNSW Sydney, the University of Sydney, and the University of Wollongong.

Side and top view of atom probe tomography data of CZTSSe showing zinc atoms (green) and sodium oxide atoms (blue) highlighting a grain boundary.

Her team is also investigating a related kesterite material CZTSSe (Cu2ZnSn(S,Se)4), where some of the sulfur is replaced with selenium. Prof. Hao’s team have achieved 12.5% efficiency with this material and, by using our microscopy, have recently identified some factors that are limiting its performance, clearing the way for further improvements.


More efficient CZTS/Se will reduce emissions and environmental impact through:

  • increasing the range of surfaces that can be used for generating electricity
  • cheap and efficient solar energy options
  • non-toxic components that are safe and easy to recycle contributing to a circular economy.

J. Li et al., Adv Materials 2020
DOI: 10.1002/adma.202005268

J. Li et al., Nature Energy 2022
DOI: 10.1038/s41560-022-01078-7


August 2, 2023