UNSW scientists surpass 10% efficiency with CZTS PV cell

Researchers at UNSW have surpassed 10% efficiency for a cell based on copper zinc tin sulfide – sulfide kesterite. It is the fourth time in two years the group has set a new record for the efficiency of cells based on such materials.

August 8, 2018 Mark Hutchins

A new UNSW research project will attempt to improve the quality of advanced solar PV cells.

Image: UNSW

UNSW scientists have surpassed 10% efficiency on a CZTS solar cell. The 1.11cm² PV cell represents the first time such efficiency has been achieved at the centimeter scale. The world record for a CZTS cell was set at 12.6% by Japanese thin film producer Solar Frontier in 2013. This, however, was achieved using a cell measuring just 0.4cm².

The research group that broke the record, led by UNSW Scientia Fellow Xiaojing Hao, also holds the efficiency record for a ‘full size’ CZTS device, at 7.6%.

The Cu₂ZnSnS₄ solar cells with over 10% power conversion efficiency enabled by heterojunction heat treatment study, published in the journal Nature Energy, describes a heat treatment which reduces recombination in the cell, increasing efficiency.

Though its efficiency is far below today’s commercial solar products, CZTS is a popular material for researchers looking to create new highly efficient cell concepts thanks to its use of cheap, abundant and non-toxic materials, as well as its flexibility in production.

CZTS in tandem cells

The UNSW researchers point out that with further boosts to efficiency, CZTS would offer several advantages over current thin film PV technologies, eliminating a reliance on rare, expensive materials such as indium, or toxic substances such as cadmium. The cells could also be suitable for flexible applications as well as tandem cells.

“CZTS-related material has a chance to be used in a tandem cell with silicon, as its bandgap can be easily tuned over a wide range when alloying with other elements, making it well matched to the high bandgap requirements for the upper cells of tandem stacks,” says Xiaojing. “The key prerequisite for such development is we need to get the efficiency of CZTS to beyond 20 per cent for us to see total energy efficiency of more than 30 per cent.”

Xiaojing plans to seek funding for a project investigating CZTS technology at the end of the year, and believes her team are on track to achieve further efficiency increases. She is also working on a project with UNSW professor Martin Green, investigating similar materials as candidates for tandem cells with silicon. “For each efficiency change, we need a step-change technology,” adds Xiaojing. “With CZTS, there are still so many things that we don’t know. Unravelling these unknowns is the most exciting adventure.”

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