Facile Molecular Approach to Transparent Thin-Film Field-Effect Transistors with High-Performance Using New Homo- and Heteroleptic Indium(III)-Tin(II) Single-Source Precursors

摘要

Various routes to new molecular bimetallic indium(III)-tin(II) alkoxides precursors for low-temperature synthesis of conducting tin-rich indium tin oxide were investigated. The studies include the facile syntheses, spectroscopic properties, and structural characterization of the new homo- and heterolepitic bimetallic alkoxides (~tBuO)Sn(μ-O~tBu)2InX2 (X = O~tBu (1), N(SiMe3)2 (2)) as well as the first heptanuclear bimetallic chlorides, that is, the oxo tert-butoxide clusters In3Sn4(O~tBu)6Cl6O2~+ Cl~-(3) and In3Sn4(O~tBu)6Cl7O_(2*)In3Sn4(O~tBu)7Cl6O2 (4). To evaluate the suitability of 1 and 2 as single-source precursors (SSPs) for the preparation of tin-rich indium tin oxide (ITO) thin films, their thermal degradation under dry synthetic air was investigated and the resulting materials were analyzed by a combination of different analytical techniques such as powder X-ray diffraction analysis (PXRD), transmission electron microscopy (TEM), FT-IR, scanning electron microscopy (SEM), energy-dispersive X-ray analysis EDX, elemental analysis, and inductively coupled plasma optical emission spectrometry (ICP-OES). Thermal treatment of 1 and 2 resulted in amorphous tin-rich ITO and crystalline ITO with traces of the cassiterite phase of tin dioxide. Incorporation of tin into the indium oxide lattice on atomic scale in crystalline ITO is evidenced by the increased lattice parameters extracted from the PXRD measurements. Results of the SEM-mapping show homogeneous distribution of indium and tin in the materials. The final In:Sn ratio of the as-prepared materials as determined by means of the ICP-OES analysis is close to that of the In:Sn ratio of 1:1 in the molecular precursors, thus confirming the suitability of 1 and 2 as SSPs to produce tin-rich ITO. Thin film field effect transistors were fabricated by spin-coating of Si-wafers with a solution of 2 in toluene and subsequent calcination under dry air. The as-prepared FETs from 2 exhibit excellent performance as shown by a field effect mobility of 3.7 X 10~(-1)cm~2V~(-1)s at 350 °C and an I_(on/off) current ratio of 1 X 10~7.