Fluorine Tweaks Push Organic Transistor Performance to New Heights

Organic field-effect transistors, or OFETs, sit at the heart of a growing family of flexible electronics: printed sensors, memory devices, inverters, and the test structures researchers use to probe how well new semiconducting materials move charge. A new review published in the Journal of Materials Science argues that one of the most powerful levers for improving these devices is also one of the smallest atoms on the periodic table. Written by Yiwei Li, Xuran Wang and colleagues at the Beijing Institute of Graphic Communication, the review systematically surveys how fluorine substitution reshapes the energy levels, packing behavior, and stability of π-conjugated molecules and polymers, and it concludes that fluorination is among the most reliable strategies for boosting device performance.

The central insight of the review is that fluorination acts on organic semiconductors through several distinct mechanisms at once. First, fluorine is highly electronegative, so attaching it directly to a conjugated backbone pulls electron density away from the π-system and lowers the lowest unoccupied molecular orbital, the LUMO. That single change can flip a material’s transport character from p-type, where holes carry the current, to ambipolar or even n-type, where electrons dominate. Because n-type and ambipolar materials are historically harder to make than their p-type counterparts, this energy-level tuning has opened the door to organic complementary circuits that were long impractical.

Second, fluorination dramatically improves ambient stability. Many high-mobility n-type semiconductors degrade in air because oxygen and water attack the electron-transporting state. Lowering the LUMO makes the material less vulnerable to this oxidative damage, so fluorinated derivatives of perylene diimides, naphthalene diimides, and related electron-deficient cores can keep working in unencapsulated devices. The review traces this theme from early air-stable n-channel materials through to modern polymers that maintain electron mobility even at very high relative humidity.

Third, fluorine engages in weak but consequential noncovalent interactions. Fluorine atoms can form halogen-bond-like contacts with sulfur, hydrogen, and other atoms in neighboring molecules, and these interactions act as conformational locks that planarize the backbone and guide how molecules stack in the solid state. Because charge-carrier mobility in organic semiconductors depends directly on how well molecules pack and how easily electrons hop or delocalize between them, these subtle structural effects translate into measurable gains in transistor performance.

The review organizes the field into two broad categories based on where the fluorine ends up. The first category covers fluorine atoms placed directly on the conjugated main chain. This includes fully perfluorinated systems, such as tetradecafluorosexithiophene and perfluoropentacene, which demonstrated that complete fluorination can produce genuine n-type transport and even p–n junctions and complementary circuits when paired with their hydrogenated analogues. It also includes molecules terminated with fluorobenzene groups and systems in which the number and position of fluorine substituents are varied systematically to fine-tune packing and transport.

Position matters as much as quantity. Studies of isoindigo-based polymers, diketopyrrolopyrrole copolymers, and fluorinated benzothiadiazole units show that moving a fluorine atom from one ring position to another can change backbone planarity, side-chain orientation, and thin-film microstructure, sometimes with opposite effects on hole and electron mobility. The review highlights cases where regioselective fluorination enabled ultrahigh intrinsic mobility by tightening crystal packing, alongside cautionary examples where fluorination introduced charge trapping and operational instability, a reminder that the technique must be applied with structural precision.

The second category shifts the fluorine away from the backbone and into the side chains, in the form of trifluoromethyl groups and semifluoroalkyl chains. Here the benefits are different in kind. Fluoroalkyl chains improve solubility and processability, enhance ambient stability by shielding the reactive backbone, and, remarkably, can drive self-organization within thin films. Because fluorinated and non-fluorinated segments tend to segregate, semifluoroalkyl side chains can promote edge-on orientation of polymer backbones relative to the substrate, the geometry that favors in-plane charge transport, and can encourage the growth of large crystalline domains during solution processing.

This side-chain engineering has produced some of the field’s most striking results. Semifluorinated side chains have been used to build polymers whose solubility switches reversibly with temperature, enabling environmentally friendly patterning and self-organized high-mobility films. Fluoroalkylated naphthalene diimide and naphthodithiophene diimide derivatives have delivered air-stable, high-electron-mobility transistors, while trifluoromethyl-substituted oligomers achieved very high electron mobility in early n-channel devices. The review notes that when stability and solution processability are the priority, fluoroalkyl substitution often outperforms direct ring fluorination.

The two strategies are increasingly combined. Recent work pairs backbone fluorination with side-chain fluorination to simultaneously lower energy levels, lock molecular conformation, and control film morphology, and fluorinated side chains terminated with polar groups have been applied to n-type organic thermoelectrics to improve both performance and air stability. The authors argue that this dual-modulation mindset, treating fluorination as a tunable design parameter rather than a binary choice, is what allows chemists to balance the competing demands of mobility, stability, and manufacturability.

For a field racing toward printable, flexible, and wearable electronics, the message of the review is that fluorine offers a rare combination of predictability and versatility. By showing precisely how fluorination position, density, and location, backbone versus side chain, map onto energy levels, packing motifs, crystallinity, and device metrics, the authors provide a practical design guide for the next generation of organic semiconductors. As OFETs move from laboratory curiosities toward commercial sensors and circuits, the smallest substituent in organic chemistry looks set to remain one of its most powerful.

Subject of Research: Fluorine modification of π-conjugated semiconductors for organic field-effect transistors

Article Title: Review: fluorine-modified π-conjugated molecules/polymers for organic field-effect transistors-a boost to devices performance

Article References: Li, Y., Wang, X., Ji, Y., Li, Q., Li, Z., Du, S., Feng, Y., Wu, T., Liu, S., & Yu, Z. (2026). Review: fluorine-modified π-conjugated molecules/polymers for organic field-effect transistors-a boost to devices performance. Journal of Materials Science, 61(42), 32391-32433. https://doi.org/10.1007/s10853-026-13597-9

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13597-9

Keywords: organic field-effect transistors, fluorination, organic semiconductors, π-conjugated polymers, charge transport, LUMO energy levels, ambient stability, fluoroalkyl side chains, molecular packing, n-type semiconductors, thin-film crystallinity, materials science