A team of researchers from DGIST has put forth a novel proposal regarding the defect energy level in the absorption layer of kesterite thin-film solar cells. By conducting admittance spectroscopy, they were able to identify specific types of defects in collaboration with Professor Kim Jun-Ho from Incheon National University’s Department of Physics.
Solar cells, known for their ability to convert sunlight into electrical energy, play a vital role in sustainable renewable energy sources. Kesterite thin-film solar cells, in particular, offer the advantage of being composed of abundant elements such as copper, zinc, tin, sulfur, and selenium, thereby addressing resource scarcity and supply instability.
Nevertheless, the low efficiency of kesterite thin-film solar cells poses a challenge that needs to be overcome for widespread adoption and market expansion. Understanding the defect properties within the light-absorbing layer is critical to improving efficiency.
Defects within the light-absorbing layer of a solar cell can impede carrier recombination, while defect clusters have the potential to alter the energy absorption band (band gap) in the light-absorbing layer. These phenomena can reduce carrier lifetime and diffusion length. Hence, identifying the specific defect or defect cluster that affects these properties is of utmost importance.
In this study, the researchers examined the characteristics of defects and defect clusters in the kesterite polished-surface light depth-dependent absorption layer using admittance spectroscopy. They found that areas with significant elemental variations in the light absorption layer were more prone to the formation of defects and defect clusters. Notably, defects with deep energy levels exceeding 150 meV had a severe detrimental impact on the properties of kesterite thin-film solar cells.
Due to the limited carrier mobility in kesterite thin-film solar cells, the researchers discovered that carrier diffusion length decreased further as the defect energy level deepened on the surface of the light-absorbing layer. Consequently, the electric current properties diminished. The primary reason for this degradation was attributed to significant fluctuations in the band gap caused by the defect, leading to increased carrier recombination and shorter carrier lifetimes, thereby reducing voltage and electric current properties.
The implications of this study are substantial, as it emphasizes the importance of preventing the formation of defects with deep energy levels at the interface of the light absorber layer to enhance the efficiency of kesterite thin-film solar cells. The research team provided a range of main defect energy levels exceeding 150 meV based on experimental results and identified the specific types of defects involved.
Senior Researcher Yang Kee-Jeong from DGIST’s Division of Energy Technology stated, “This study’s approach is expected to offer valuable insights for understanding defect properties and improving the efficiency not only of kesterite thin-film solar cells but also other types of solar cells.”
The findings of this study have been published in the journal Carbon Energy.
Source: DGIST (Daegu Gyeongbuk Institute of Science and Technology)
