A team of senior researchers, including Kee-jeong Yang, Dae-hwan Kim, and Jin-gyu Kang from the Division of Energy & Environmental Technology, DGIST (President Kunwoo Lee), collaborated with Prof. Kim Jun-ho's team from the Department of Physics, Incheon National University and Prof. Koo Sang-mo's team from the Department of Electronic Materials Engineering to significantly improve the performance of kesterite (CZTSSe) thin-film solar cells in joint research. They developed a new method for doping silver (Ag) in solar cells to suppress defects that hinder cell performance and promote crystal growth, thereby dramatically increasing efficiency and paving the way for commercialization.
CZTSSe solar cells are composed of copper (Cu), zinc (Zn), tin (Sn), sulfur (S), and selenium (Se), and are gaining attention as a resource-abundant, low-cost, and eco-friendly solar cell technology. In particular, they have the advantage of being suitable for large-scale production and highly competitive in price because they use materials that are abundant in resources instead of the scarce metals used in conventional solar cells. However, conventional CZTSSe solar cells have low efficiency and high current losses due to electron-hole recombination, thus making them difficult to commercialize.
To address these issues, the research team employed a method of doping the solar cell precursor with Ag. Ag inhibits the loss of Sn and helps the materials mix better at low temperatures. This allows the crystals to grow larger and faster, reducing defects and improving the performance of the solar cell. In this study, they systematically analyzed how the placement of Ag at different locations in the precursor changes the defects and electron-hole recombination properties in the solar cell. The results indicate that Ag can significantly improve the performance of the solar cell by preventing Sn loss and maximizing the defect suppression effect.
Importantly, they also found that doping Ag in the wrong place actually interferes with the formation of Zn and Cu alloy, causing Zn to remain in the bulk and form defect clusters. This can lead to increased electron-hole recombination losses and degraded performance. From this, the research team offered an important insight: solar cell performance varies significantly depending on where Ag doping occurs.
Furthermore, the research team found that the liquid material formed by Ag doping promotes crystal growth, significantly improving the density and crystallinity of the absorber layer. This resulted in an improved energy band structure and fewer defects, ultimately allowing for smoother charge transport in the cell. These findings are expected to contribute significantly to the production of high-performance solar cells at low cost.
"In this study, we analyzed the effect of Ag doping, which had not been clearly identified before, process by process, and found that silver plays a role in suppressing tin loss and improving defects," said Yang Kee-jeong, a senior researcher at the Division of Energy & Environmental Technology. "The results provide important insights into the design of silver-doped precursor structures to improve solar cell efficiency and are expected to contribute to the development of various solar cell technologies."
The research was funded by the Ministry of Science and ICT's Source Technology Development (Leapfrog Development of Carbon Neutral Technology) Program and the Future-Leading Specialization Research (Grand Challenge Research and Innovation Project (P-CoE)) Program. The paper was published online in the Energy & Environmental Energy (IF 32.4), a leading international journal in the field of energy.
