Engineers at the University of New South Wales (UNSW) have achieved a world-record efficiency of 13.2% for kesterite (CZTS) solar cells, marking a leap forward in tandem solar cell technology.
Photovoltaic (PV) researchers the world over have been investigating the best materials to combine with tradition silicon cells to form “tandem” cells, boosting efficiency compared to a single junction solar cell.
Scientia Professor Xiaojing Hao and her team from UNSW’s School of Photovoltaic and Renewable Energy Engineering have achieved a best-ever efficiency of 13.2% for high bandgap kesterite solar cells, which had been enhanced with hydrogen.
Kesterite is a naturally occurring mineral that’s more commonly created artificially from a combination of copper, zinc, tin and sulphur, leading many to refer to the abundant, non-toxic substance as CZTS.
“The big picture here is that we ultimately want to make electricity cheaper and greener to generate,” says Professor Hao.
“Silicon modules have almost reached the limit of their theoretical efficiency, so what we are trying to do is answer the question coming from the PV industry as to what the next generation of cells will be made of.
“And as well as that, how can we make solar panels less expensive to manufacture, and how can we get more electricity per area so the panels can be particularly beneficial for area-limited PV applications?”
Overcoming material defects
Using CZTS materials in PV technology isn’t a new concept; CZTS are environmentally friendly, cost-effective to manufacture and offer a strong PV performance over a long life span.
Unfortunately, they tend to be inefficient due to the high number of defects introducing during the manufacturing process.
The UNSW team has overcome some of the challenges inherent in the manufacturing process by “annealing” or heat-treating the solar cell device in a hydrogen-rich atmosphere, thereby reducing defects in the resulting material.
“What we have shown in this work is that introducing hydrogen can ensure those defects have less of an impact – which is known as passivation,” Hao said.
Prof. Hao is hopeful the new breakthrough will accelerate the chances of CZTS reaching 15% efficiency within the next year and expects commercialisation of the technology to be achieved by 2030.
“There is still work to be done to find ways to further reduce the defects we find in CZTS, either during the fabrication or via post-fabrication treatments,” she says.
“But we know that this is a good material. When we consider the requirements from the bottom up, we know that we need something that is widely abundant, that is environmentally friendly, that has good optoelectronic properties and can last a long time – and CZTS fits the bill.”