Polymer stabilized ZnO nanoparticles for low-temperature and solution-processed field-effect transistors

Abstract

Homogeneous, smooth and densely-packed nanoparticulate ZnO films for field-effect transistors (FETs) are formed by spin-coating suspensions of ZnO nanoparticles in an organic solvent, followed by baking at 150 °C. The morphology of the films is strongly dependent on the type and amount of surfactant polymers that are employed to cap ZnO nanoparticles and stabilize the suspensions. Infrared spectroscopy, atomic force microscopy, electron microscopy and electrical characterization reveal that a certain amount of surfactant is needed to make the size of the agglomerates small enough to form such nanoparticulate films; however, an excess amount of surfactant results in an increase in the resistivity of the nanoparticulate films owing to the electrically semi-insulating nature of the surfactants. FETs composed of the nanoparticulate ZnO films in the bottom gate configuration operate in the n-channel enhancement mode with a clear saturation current at higher drain voltages. The field-effect mobility of the FETs varies by more than three orders of magnitude dependent on the type and amount of surfactants, exhibiting the highest value of 8 × 10⁻³ cm² V⁻¹ s⁻¹. This clearly indicates that the appropriate development and synthesis of surfactants for inorganic nanocrystal suspensions are highly important for low-temperature and solution-processed FETs, compatible with plastic substrates, towards printable electronics.