image: Recently, Wei Deng and colleagues from Soochow University, China, proposed a transparent electrical contact concept for improving the performance of organic transistors. This work was recently published in National Science Review.
Credit: ©Science China Press
“Magic Molecules” Unlocks High-Performance Flexible Electronics
In a groundbreaking development for organic electronics, a team of Chinese scientists has devised a novel method using fluorinated thiol molecules to dramatically enhance the performance of single-crystal organic thin-film transistors (SC-OTFTs). The study demonstrates how these "magic molecules" can significantly reduce electrical resistance at metal-semiconductor interfaces, paving the way for next-generation flexible devices such as bendable displays, wearable health monitors, and advanced IoT sensors.
The Challenge: Imperfections at the Buried Contact Interfaces in Organic Transistors
Organic semiconductors offer unique advantages for flexible electronics due to their lightweight, bendable nature. However, creating reliable electrical contacts between metal electrodes and organic single-crystalline films (OSCFs) has long been a hurdle. Traditional metal deposition methods, such as thermal evaporation, often damage the delicate organic surfaces, introducing trap states that hinder electron flow and degrade device performance. These imperfections lead to high contact resistance and unstable operation, limiting the practical use of organic transistors in real-world applications.
The Breakthrough: Molecule Upgrading Engineering at the Buried Interface
Led by researchers from Soochow University, the team introduced a game-changing solution: using pentafluorobenzenethiol (PFBT), a fluorinated thiol molecule, to upgrade buried metal-OSCF contacts through an in-situ chemical reaction. Unlike traditional approaches that rely on additional interlayers or complex processes, this method leverages PFBT’s ability to spontaneously form strong bonds with metal electrodes (such as silver) while filling interfacial trap states in the organic semiconductor layer. "PFBT acts as a dual-functional molecular engineer," explains Dr. Wei Deng, one of the study’s corresponding authors. "Its sulfur atoms form robust bonds with silver, increasing the metal’s work function and reducing the energy barrier for charge injection. Meanwhile, its fluorine-rich structure donates electrons to fill trap states in the organic layer, effectively repairing the interface and eliminating resistance."
Performance Improvements
Compared to untreated devices, SC-OTFTs with PFBT-upgraded contacts exhibit: A 16-fold reduction in contact resistance, dropping from 1,314 Ω·cm to just 79.7 Ω·cm, allowing carriers to flow more freely; A 73.3% decrease in Schottky barrier height, from 150 meV to 40 meV, significantly enhancing charge injection efficiency; A high average reliable mobility of 13.2 cm²/V⁻¹s⁻¹ (a measure of how quickly carriers move through the material), paired with an impressive reliability factor of 89%.
These improvements translate to transistors that operate with near-ideal efficiency, featuring a near-zero threshold voltage (-0.47 V) and a low subthreshold swing (136 mV/dec), even at low supply voltages as low as -5 V. Such advancements address long-standing challenges in organic electronics, where high performance and reliability have been difficult to achieve simultaneously.
A Versatile Solution for Flexible Electronics
The PFBT-based method is not only effective but also versatile. It works with various organic semiconductors, including both p-type (such as C8-BTBT, the study’s model material) and n-type materials, as well as polymer semiconductors. The team successfully fabricated arrays of 72 devices with remarkable uniformity, demonstrating the technique’s scalability for large-area manufacturing—a critical step toward application.
"One of the most exciting aspects is the method’s simplicity," notes Dr. Yongji Wang, a lead author of the study. "By integrating PFBT into the solution during film formation, we achieve in-situ interface modification without additional processing steps. This makes it compatible with roll-to-roll printing techniques, ideal for mass-producing flexible electronics."
A Milestone in Organic Electronics
The study represents a significant milestone in the field, combining molecular-level interface engineering with practical device performance. By addressing the core issue of contact resistance and trap states, the Soochow University team has unlocked the full potential of organic semiconductors, proving they can rival traditional inorganic thin-film transistors in performance while offering unmatched flexibility.
As the research community and industry alike embrace this innovation, the future of electronics looks increasingly flexible—both in form and function. With further development, molecular upgrading could become a standard technique in the manufacturing of high-performance organic devices, driving advancements in technology that are as elegant as they are revolutionary.