Yaochuan Mei

High Mobility Field‐Effect Transistors with Versatile Processing from a Small‐Molecule Organic Semiconductor

Trialkylgermyl functionalization allows the development of high-performance soluble small-molecule organic semiconductors with mobilities greater than 5 cm(2) V(-1) s(-1) . Spray-deposited organic thin-film transistors show a record mobility of 2.2 cm(2) V(-1) s(-1) and demonstrate the potential for incorporation in large-area, low-cost electronic applications.

Vibration‐Assisted Crystallization Improves Organic/Dielectric Interface in Organic Thin‐Film Transistors

Solution processability of organic semiconductors allows high-throughput fabrication on arbitrary substrates at low-cost, but the films often exhibit low performance. Here, we report on a new method for device fabrication, vibration assisted crystallization (VAC) that produces superior films, which approach the fundamental performance limits shown in corresponding single-crystal measurements.

Quantitative analysis of the density of trap states at the semiconductor-dielectric interface in organic field-effect transistors

The electrical properties of organic field-effect transistors are governed by the quality of the constituting layers, and the resulting interfaces. We compare the properties of the same organic semiconductor film, 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene, with bottom SiO2 dielectric and top Cytop dielectric and find a 10× increase in charge carrier mobility, from 0.17 ± 0.19 cm2 V−1 s−1 to 1.5 ± 0.70 cm2 V−1 s−1, when the polymer dielectric is used. This results from a significant reduction of the trap density of states in the semiconductor band-gap, and a decrease in the contact resistance.

Crossover from band-like to thermally activated charge transport in organic transistors due to strain-induced traps

Significance The operation of organic field-effect transistors is governed by the processes taking place at the device interfaces. The mismatch in the coefficients of thermal expansion of the consecutive layers can induce inhomogeneous strain in the organic semiconductor layer and reduce performance by increasing the electronic trap density. We show that a high-quality organic semiconductor layer is necessary, but not sufficient, to obtain efficient charge-carrier transport, and we propose a device design strategy that allows us to achieve the intrinsic performance limits of a given organic semiconductor regardless of the relative thermal expansions of the constituent layers. The temperature dependence of the charge-carrier mobility provides essential insight into the charge transport mechanisms in organic semiconductors. Such knowledge imparts critical understanding of the electrical properties of these materials, leading to better design of high-performance materials for consumer applications. Here, we present experimental results that suggest that the inhomogeneous strain induced in organic semiconductor layers by the mismatch between the coefficients of thermal expansion (CTE) of the consecutive device layers of field-effect transistors generates trapping states that localize charge carriers. We observe a universal scaling between the activation energy of the transistors and the interfacial thermal expansion mismatch, in which band-like transport is observed for similar CTEs, and activated transport otherwise. Our results provide evidence that a high-quality semiconductor layer is necessary, but not sufficient, to obtain efficient charge-carrier transport in devices, and underline the importance of holistic device design to achieve the intrinsic performance limits of a given organic semiconductor. We go on to show that insertion of an ultrathin CTE buffer layer mitigates this problem and can help achieve band-like transport on a wide range of substrate platforms.