Xiaojing Hao

We think we have developed the lift-off technology needed to take this new solar cell to the next level.
Solar energy will be crucial if we are to overcome our reliance on fossil fuels. Xiaojing Hao is developing next-generation photovoltaic technology from abundant, non-toxic minerals to transform the global solar market.

To prevent the catastrophic impacts of climate change, we need to phase out fossil fuel power generation – and fast.

One of the most attractive clean energy alternatives are solar photovoltaic (PV) cells, which can be deployed on rooftops or on building facades, and at utility-scale in power stations.

Currently, silicon-based solar cells dominate the PV market, making up 90% of commercially available products. The ongoing challenge is lowering costs while improving energy conversion efficiency, turning more sunlight into usable power. 

One approach to improving efficiencies is layering thin film solar cells, made from other high band gap semiconducting materials, on top of low band gap cells. This process enables the capture and conversion of more energy from sunlight.  

One of the best commercial thin-film single junction cells, which can also be combined with other cells by the "tandem architecture" approach, is made from copper, indium, gallium and selenide (CIGS). 

“But the one Achilles heel of CIGS solar cells is the production and price volatility of the rare-earth material indium,” says Dr Xiaojing Hao, a solar engineer from the UNSW School of Photovoltaic & Renewable Energy Engineering.   

As touch screen devices become more ubiquitous, the cost of indium is projected to rise, potentially limiting wider deployment, as solar manufacturers strive to keep costs low. 

Hao is developing a promising, low-cost alternative using copper, zinc, tin and sulfide (CZTS) – all of which are abundant, non-toxic materials. One of the benefits is that the cells could find deployment in countries where chemical regulations have traditionally posed barriers.

Hao, who has been studying and working at UNSW under the supervision of world-leading solar pioneer Scientia Professor Martin Green since 2006, has been optimising the design of the new cells to improve electrical potential while developing scalable fabrication pathways, enabling the technology to be easily taken up by industry.

She expects her group to exceed 10% efficiency by early 2016, and has a target of achieving a new world record for CZTS solar cells of 15% within three years – a milestone she says will prompt “a lot of interest from industry”.

“We think we have developed the lift-off technology needed to take this new solar cell to the next level,” she says. “I believe we can make this solar cell much better.”

Hao has already been working with Chinese steel manufacturer, Baosteel, through an Australian Research Council Linkage Grant, to incorporate these low-cost solar cells onto steel building materials.

Not all solar cells are compatible with steel, because during the manufacturing process, heat treatment can cause iron from the steel to diffuse into the solar cell, dampening its electrical potential, explains Hao. But her team has worked out how to prevent this diffusion.

“It could have a big future in the rooftop PV market and in building integrated PV, and it could make a huge difference to people’s lives around the world.”