Evaluation of Effective Field-Effect Mobility in Thin-Film and Single-Crystal Transistors for Revisiting Various...

The magnitude of the field-effect mobility μ of organic thin-film and single-crystal field-effect transistors (FETs) has been overestimated in certain recent studies. These reports set alarm bells ringing in the research field of organic electronics. Herein, we report a precise evaluation of the μ values using the effective field-effect mobility, μ_eff, a new indicator that is recently designed to prevent the FET performance of thin-film and single-crystal FETs based on various phenacene molecules from being overestimated. The transfer curves of a range of FETs based on phenacene are carefully categorized on the basis of a previous report. The exact evaluation of the value of μ_eff depends on the exact classification of each transfer curve. The transfer curves of all our phenacene FETs could be successfully classified based on the method indicated in the aforementioned report, which made it possible to evaluate the exact value of μ_eff for each FET. The FET performance based on the values of μ_eff obtained in this study is discussed in detail. In particular, the μ_eff values of single-crystal FETs are almost consistent with the μ values that were reported previously, but the μ_eff values of thin-film FETs were much lower than those previously reported for μ, owing to a high absolute threshold voltage, |V _th|. The increase in the field-effect mobility as a function of the number of benzene rings, which was previously demonstrated based on the μ values of single-crystal FETs with phenacene molecules, is well reproduced from the μ_eff values. The FET performance is discussed based on the newly evaluated μ_eff values, and the future prospects of using phenacene molecules in FET devices are demonstrated.