Impact of surfactants covering ZnO nanoparticles on solution-processed field-effect transistors: From dispersion state to solid state
Résumé
Solution-processed n-channel oxide semiconductor thin-film transistors (TFTs) were fabricated using zinc oxide (ZnO) nanoparticles. The solution-processable semiconductor dispersions based on ZnO were prepared by dispersing the synthesized ZnO nanospheres in solution. The dispersion state was strongly affected by either the surfactant type or the solvent nature. Two small organic molecules commercially available, ethanolamine (EA) and benzoic acid (BA), were used as surfactant in alcohol solvent. The introduction of EA reduced the size of nanocrystal agglomerates and improved their dispersion properties simultaneously. Spin-coating of EA-modified ZnO dispersion following by a low-temperature annealing produced uniform polycrystalline nanoparticulate thin films. The resulting solid state of thin films demonstrated that the incorporation of EA has not a direct impact on the morphology but slightly decrease the field-effect mobility by less than one order of magnitude due to the insulating properties of EA organic molecules grafted on ZnO particles. As contrary, BA generated the existence of large-size cohesive ZnO agglomerates in solution which persist in the solid state to generate a less efficient charge transport. The modification of the particles surface by capping agent and the resulting particle-particle interactions in thin films were attributed as the main factors to impact on the field-effect mobility. To surfactant-free dispersions, the cohesive forces in ZnO agglomerates have been strongly influence by the solvent nature for a balance between a suitable dispersity of solution state and an effective solid state to charge transport. (C) 2016 Elsevier B.V. All rights reserved.