A new precursor route to semiconducting Zinc Oxide

We demonstrate a new precursor route towards solution- processed films of the II-VI semiconductor Zinc oxide (ZnO). Spray pyrolysis of aqueous solutions of the Zinc salt Zinc chloride (ZnCl2) onto a substrate heated to at least 250 oC gives films that are insoluble in water, display an absorption edge at 365 nm, and when electrically gated display thin film transistor characteristics similar to ZnO films derived via the established Zinc Acetate (ZnAc) precursor route; we therefore identify it as ZnO. Control experiments attempting spray pyrolysis of aqueous Zinc sulfate solutions, and delayed pyrolysis of cold- sprayed and dried ZnCl2 films, do not lead to semiconducting films. Formation of ZnO from an aqueous Zinc salt requires the simultaneous presence of Zinc ions, Chloride ions, and water, at the time of pyrolysis. We therefore suggest the actual ZnO precursor is the ZnClxH2O(4−x) species that forms when ZnCl2 dissolves in water [The Journal of Chemical Physics 39, 3436 (1963)]. The reported process is easy to upscale for large area ZnO coatings, e.g. on window panes for thermal control, as no organic solvent vapours are released

A membrane- free cation selective water- gated transistor

Sensors for the detection of waterborne cations are of great practical interest, and chemistry has synthesised a formidable catalogue of cation selective complexation agents (‘ionophores’) as selective sensitisers (e.g. 9-13, 15-19, 28, 29). Current ionophore- based sensors separate the complexation of the cation by the ionophore, and the transduction of complexation into an electrical signal, into separate components. We here unite both functions into a single, sensitised semiconducting layer of a water- gated organic thin film transistor (OTFT). The resulting OTFT transduces waterborne cations into an electrical signal with same selectivity, sensitivity, and limit of detection as established sensors at much simplified preparation and operation. This opens a new route to apply the ‘ionophore’ family of functional organic materials in practical cation sensors

An ionic liquid-gated polymer thin film transistor with exceptionally low "on" resistance

We report the ionic liquid (IL) gating of a solution processed semiconducting polymer, poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). IL gating relies on the poor solubility of PBTTT, which requires hot chlorinated benzenes for solution processing. PBTTT, thus, resists dissolution even in IL, which otherwise rapidly dissolves semiconducting polymers. The resulting organic thin film transistors (OTFTs) display low threshold, very high carrier mobility (>3 cm2/Vs), and deliver high currents (in the order of 1 mA) at low operational voltages. Such OTFTs are interesting both practically, for the addressing of current-driven devices (e.g., organic LEDs), and for the study of charge transport in semiconducting polymers at very high carrier density

Precursor- route ZnO films from mixed casting solvent for high performance aqueous electrolyte- gated transistors

We significantly improved the properties of semiconducting zinc oxide (ZnO) films resulting from the thermal conversion of a soluble precursor, zinc acetate (ZnAc), by using a mixed casting solvent for the precursor. ZnAc dissolves more readily in a 1:1 mix of ethanol (EtOH) and acetone than in either pure EtOH, pure acetone, or pure isopropanol, and ZnO films converted from mixed solvent cast ZnAc are more homogeneous. When gated with a biocompatible electrolyte, phosphate buffered saline (PBS), ZnO thin film transistors (TFTs) derived from mixed solvent cast ZnAc give 7 times larger field effect current than similar films derived from ZnAc cast from pure EtOH. Sheet resistance at VG = VD = 1V is 18 kΩ/▢, lower than for any organic TFT, and lower than for any water- gated ZnO TFT, reported to date