Australian Researchers Improve Solar Cell Efficiency Using Baking Techniques
When discussing the process of manufacturing solar cells, likening it to cake baking might not be the first comparison that springs to mind. However, engineers from the University of New South Wales (UNSW) believe that this culinary skill can help them improve the efficiency of tandem solar cells.
Leading a team of researchers, Scientia Professor Xiaojing Hao from the School of Photovoltaic and Renewable Energy Engineering at UNSW is exploring how baking techniques can shed light on enhancing solar cell technology.
The Potential of CZTS in Solar Technology
The researchers are focusing on a material called CZTS, which stands for copper, zinc, tin, and sulphur. This compound presents an interesting possibility for tandem solar cell semiconductors due to its abundance and environmental benefits compared to some traditional semiconductor materials.
Nonetheless, CZTS has yet to achieve the required efficiency metrics for commercial usage, primarily due to the formation of minor defects during its production.
Understanding Defects Through Baking
According to the UNSW scientists, the key issue with CZTS semiconductors lies in the little imperfections created during the material’s manufacturing process. Professor Hao explains this with the baking analogy: “When you bake a cake, you mix the ingredients and place it in the oven; similarly, we put our solar cell materials in a furnace.”
However, just like baking requires more than merely combining ingredients, solar cell creation involves ensuring an even distribution of components throughout the thermal processing. “The journey is just as vital as the end product,” Hao notes, emphasising the need for careful control from the outset to mitigate defects in the CZTS.
The Impact of Small Defects
Upon examining the initial stages of the high-temperature manufacturing, the researchers discovered that copper tends to shift away from its intended position, causing unwanted impurities and structural flaws. These seemingly minor defects can significantly hinder a solar cell’s effectiveness in converting sunlight into energy.
Professor Hao elaborates, “When one element drifts from its proper place, it initiates the formation of another material phase. As the crystal grows, it leads to impurities and imperfections, creating disarray that traps photo-generated carriers, which ultimately lowers the efficiency of the solar cells.”
The voltage output of solar cells is a direct indicator of energy loss, with detrimental defects resulting in decreased voltage levels. Defect management is therefore crucial in determining the overall efficiency and energy conversion ability of solar technology.
A Breakthrough in Efficiency
The UNSW team’s research revealed that reinforcing the bonding between copper and sulphur during the thermal reaction can significantly minimise defects. This led to a remarkable voltage performance of 12.4 per cent from this class of CZTS solar cells, though still below the efficiency levels of traditional silicon solar cells.
Despite this, the researchers view it as a significant step forward in tackling longstanding challenges within the field of solar technology. They also believe that their findings could be extended to other semiconductor materials in future solar applications, as illustrated by co-author Dr Ao Wang’s comments.
Broad Implications for Semiconductor Development
Wang points out that many researchers focus solely on getting the right mix of initial ingredients, often treating the thermal process as a “black box.” “They presume that if the ingredients are well mixed, the resulting solar cell will be optimal,” he explains. “However, if elements begin separating early in the process, even a perfect recipe may yield subpar results.”
This principle applies not just to CZTS but also to various complex semiconductor materials comprised of multiple chemical elements, making them prone to similar manufacturing challenges.
Professor Hao stresses the critical nature of regulating the conditions of ingredients during the manufacturing process. “Our developed defect control strategy will prove invaluable for the design and optimisation of other compound semiconductors,” she affirms. “Our principles can aid in identifying suitable candidates for tandem solar cells, ensuring that our focus isn’t just on the final mix but on maintaining a uniform distribution from the very beginning.”
This methodology, while applicable to other semiconductor compositions, relies on fundamental design principles that remain consistent across different materials.
