UNSW researchers are consistently leading the development of CZTS solar cell technology, and recently achieved a 13.2% efficiency record with a laboratory scale cell. At the same time, Energy Nature is featuring their previous CZTS record efficiency in its January 2025 edition.
CZTS is the sythetic form of kesterite and is an exciting top cell contender for tandem solar cells which combine two photovoltaic materials (ie. silicon and kesterite, or silicon and perovskite) to capture a wider spectrum of energy from sunlight, thereby increasing the electricity conversion efficiency.
Supported by ARENA and ACAP infrastructure funding, UNSW’s Professor Xiaojing Hao, Dr Kaiwen Sun and their co-researchers have been investigating CZTS solar cell technology, or more specifically Cu₂ZnSnS₄, for 10 years and have led global development for the last eight years.
CZTS is a high-bandgap thin film, flexible material suitable for single-junction and tandem solar cells. CZTS is a compound made up of copper, zinc, tin and sulfur – four cheap and abundant elements in the Earth’s crust.
CZTS is shaping up to be an exciting alternative to the more widely-studied perovskite as a tandem top cell candidate. Unlike perovskite, CZTS is stable, and economically and environmentally favourable due to its non-toxic and abundant elements. However, CZTS has had relatively low energy conversion efficiencies.
Dr Sun said, “If the efficiency can be pushed higher, with a benchmark of 15%, it can be used as a top cell, combined with a silicon bottom cell. That’s the primary focus of our work.”
Hao and Sun achieved a record 11% CZTS cell efficiency in 2018, but progress stagnated after that. The main problem limiting the efficiency of kesterite devices is the poor collection of photogenerated carriers, as they tend to recombine while being transported. This is largely due to the number of defects created within CZTS during production.
Hao and Sun have concentrated their efforts on investigating the effect of annealing CZTS in a hydrogen-containing atmosphere.
Dr Sun said, “Hydrogen, the smallest atom, acts like a tiny helper in our solar cells. It interacts with oxygen atoms, which then influences how sodium – an element that’s hard to control directly – gets distributed. This chain reaction improves the flow of electricity in the material.”
“Using this approach, we achieved a record-breaking efficiency of 11.4% for CZTS solar cells.”
In January 2025, Nature Energy published a paper reporting on this significant achievement, Nature Energy is the sister publication to Nature, one of the most respected and widely read academic journals in the world.
Excitingly, the group have followed up with a new record breaking verified 13.2% <1cm2 CZTS cell.
Their cell is included the latest Solar Cell Efficiency Tables (Version 65) by Martin Green, et al. (2025).
“These cells are made from low-cost, environmentally friendly materials, aligning with the future direction of photovoltaics: green energy from green materials.”
Dr Sun said, "Kesterite and Sb2(S,Se)3 (Antimony chalcogenide) are the only single junction solar cells that UNSW set record efficiencies with in the latest efficiency table, except Si 25%. UNSW is leading the development of these two technologies."
The support of the Australian Centre for Advanced Photovoltaic is crucial to the team's work developing the next generation of solar technologies. Dr Kaiwen Sun has previously held an ACAP Fellowship and is currnetly an ARC DECRA Fellow.
Comments