A research team led by Professor Ji-Sang Park of the Sungkyunkwan University, SKKU Advanced Institute of Nanotechnology (SAINT), in collaboration with Professor Yong-Young Noh’s team at Pohang University of Science and Technology (POSTECH) and the teams of Professors Ao Liu and Huihui Zhu at the University of Electronic Science and Technology of China (UESTC), has successfully overcome the critical oxidation problem of conventional eco-friendly, lead-free perovskite semiconductors and developed a p-type transistor with world-class performance. The study was published in Nature, one of the world’s most prestigious scientific journals, on July 1.
Transistors are essential components that control electrical signals in countless electronic devices, including smartphones. They are broadly classified into n-type transistors, which use electrons as charge carriers, and p-type transistors, which use holes—the vacancies left by electrons. Achieving a balance between the two is essential for developing low-power, high-performance semiconductor devices. However, improving the performance of p-type transistors has remained extremely challenging and has been identified by the Ministry of Science and ICT as one of the “10 Future Challenges in the Semiconductor Field.”
Tin (Sn)-based perovskite semiconductors have attracted attention as one of the most promising eco-friendly alternatives to toxic lead (Pb), as well as strong candidates for addressing this challenge due to their excellent hole transport properties. However, when exposed to oxygen in the air, unreacted and undercoordinated tin ions on the surface are readily oxidized, creating defects that interfere with charge transport. This long-standing problem causes the performance and lifetime of the semiconductor to deteriorate rapidly.
To address this issue, the joint research team introduced a new volatile surface reconstruction process that effectively heals chemical defects. The researchers treated the surface of a cesium–tin–iodide semiconductor with potassium acetate. During the process, unstable tin species on the surface—the primary cause of performance degradation—are converted into volatile compounds and removed from the surface. At the same time, potassium iodide naturally forms at the sites left behind by the removed tin species, creating a robust self-passivating protective layer that blocks exposure to air and moisture. In other words, the process simultaneously removes the source of defects and fills the resulting surface with a protective barrier.
Using this innovative technique, the researchers achieved world-class performance in p-type perovskite transistors, with hole mobility exceeding 50 cm²/V·s and an on/off current ratio of more than 10⁸. In particular, while conventional devices could degrade within minutes when exposed to air, the newly developed devices maintained stable operation for more than four hours under ambient conditions. They also demonstrated outstanding durability, retaining their initial performance for more than one month even under harsh thermal conditions at 100°C.
Professor Ji-Sang Park said, "Beyond simply enhancing device performance, this study was especially meaningful because we were able to identify the specific chemical reaction pathways and defect-healing principles of volatile surface reconstruction. Elucidating this mechanism in close collaboration with our domestic and international partners was deeply rewarding, especially as we expect this approach to be broadly applicable to other next-generation semiconductor materials."
This research was supported by the Leader Research Program and the Mid-Career Researcher Program of the National Research Foundation of Korea, as well as by Samsung Display.
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