A research team, led by Professor Yong-Young Noh and Dr. Youjin Reo from the Department of Chemical Engineering at POSTECH (Pohang University of Science and Technology), has developed p-channel Sn2+-halide perovskite TFTs using a thermal evaporation approach with inorganic caesium tin iodide (CsSnI3).
The project was a collaborative effort with Professors Ao Liu and Huihui Zhu from the University of Electronic Science and Technology of China (UESTC) and resulted in the development of high-performance, stable p-channel CsSnI3-based TFTs using a commercially compatible vapor-deposition approach with PbCl2 as an additive. The volatile chloride triggers solid-state reactions and the conversion of as-evaporated precursor compounds. This facilitates the formation of high-quality and uniform perovskite films, and also modulates the high hole density, making them suitable for use as channel layers. The optimized CsSnI3:PbCl2 TFTs delivered average µFE of around 34 cm2 V−1 s−1, on/off ratio of around 108 and storage stability of more than 150 days. The team also demonstrated a large-scale Sn2+-halide perovskite TFT array that overcomes the technical challenges faced in the solution process. The vapor-deposited TFTs could be used in backplanes for organic light-emitting diode displays, or in logic devices and circuits for monolithic three-dimensional integration, where low process temperatures are required.
Transistors are typically categorized as n-type (electron transport) and p-type (hole transport), with n-type devices generally demonstrating superior performance. However, to achieve applications like high speed computing with low power consumption, p-type transistors must also reach comparable efficiency.
To address this challenge, the research team focused on a novel p-type semiconducting material with a unique crystal structure: tin-based perovskites. Traditionally, it has only been fabricated through a solution process—a technique akin to soaking ink into paper—which presents challenges in scalability and consistent quality.
Now, the team successfully applied thermal evaporation, a process widely used across industries such as OLED TV and semiconductor chips manufacturing, to produce high-quality caesium-tin-iodide (CsSnI3) semiconductor layers. This technique involves vaporizing materials at high temperatures to form thin films on substrates.
Furthermore, by adding a small amount of lead chloride (PbCl2), the researchers were able to improve the uniformity and crystallinity of the perovskite thin films. The resulting transistors exhibited outstanding performance, achieving a hole mobility of over 30 cm2/V·s and an on/off current ratio of 108 which are comparable to already commercialized n-type oxide semiconductors—indicating rapid signal processing and low power consumption during switching.
This innovation not only enhances device stability but also enables the fabrication of large-area device arrays, effectively overcoming two major limitations of previous solution-based methods. Importantly, the technology is compatible with existing manufacturing equipment used in OLED display production, presenting significant potential to reduce costs and streamline fabrication processes.
“This technology opens up exciting possibilities for the commercialization of ultra-thin, flexible, and high-resolution displays in smartphones, TVs, vertically stacked integrated circuits and even wearable electronics because low processing temperature below 300 ℃,” said Professor Yong-Young Noh.
