Influence of trapping states at the dielectric–dielectric interface on the stability of organic field-effect transistors with bilayer gate dielectric

Wet-chemical treatment on the gate dielectric, i.e. tuning the chemical properties via the choice of the buffer dielectric, has been widely employed to study the morphology and growth mode of organic semiconductors (OSCs). Through these studies, further understanding of charge transport mechanisms is obtained, and the electrical performances of organic field-effect transistors (OFETs), e.g. charge carrier mobility, on/off current ratio and subthreshold swing, thus have been greatly improved. In order to achieve a useful device, its stability becomes extremely important. In this article, the study on the charge trapping at the dielectric–dielectric interface by using the combination of poly(methyl methacrylate) (PMMA) and silicon dioxide (SiO2) dual-dielectric was carried out under dark and illuminated conditions. Our results showed that the thickness of the PMMA layer, determining the film uniformity and the magnitude of charge injection barrier, plays a decisive role in the charge trapping process. With the thickness optimized, the device stability is greatly enhanced. Our findings bring about a low-cost, easy-to-realize fabrication method to produce high-performance and stable/reliable OFETs.

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► Charge trapping in buried traps between PMMA and SiO2 was investigated for both p- and n-channel OFETs.
► Trapping of minority carriers occurs only under illumination, resulting in a large shift in threshold voltage.
► High-energy non-equilibrium carriers can be easily injected across thin buffer dielectric under high electrical field.
► Buffer dielectric with optimized thickness suppresses photo-induced charge transfer, thus stabilizing threshold voltage.