Synthesis of freestanding water-soluble indium oxide nanocrystals capped by alanine nitric acid via ligand exchange for thin film transistors and effects of ligands on the electrical properties

We demonstrate synthesis of freestanding water-soluble indium oxide nanocrystals (In₂O₃ NCs) by ligand exchange to β-alanine nitric acid (Ala·HNO₃) and its application for active channel layer in thin film transistors (TFTs), with investigation of the effect of curing temperatures on the TFT properties in terms of thermal behaviour of the ligand molecules at 150, 300, and 350 °C. After ligand exchange from long alkyl ligand (myristic acid, MA) to short Ala·HNO₃, the mobility of NC TFTs cured at 150 °C increased by over 1 order of magnitude, from 1.3 × 10⁻⁴ cm²V^-1s⁻¹ to 4.5 × 10⁻³ cm²V^-1s⁻¹, due to enhanced tunnelling rate (Γ) between adjective NCs. Higher curing temperatures such as 300 and 350 °C, inducing thermal decomposition of the organic ligands, led to further enhancement of the mobility, particularly up to 2.2 cm²V^-1s⁻¹ for the In₂O₃ NC-Ala·HNO₃ TFT cured at 350 °C. It is also found that the ligand exchange of In₂O₃ NC in acidic condition (e.g. HNO₃) would be simple and effective to reduce the surface defects by surface etching, which may lead to better device performances. - Graphical abstract: Display Omitted - Highlights: • Freestanding water-soluble In₂O₃ nanocrystals (NCs) were synthesized by ligand exchange. • Thin film transistors (TFTs) of colloidal NCs were fabricated by spin-coating method. • Water-soluble In₂O₃ NC TFTs showed higher mobilities due to shorter ligand length. • Surface defects of NCs were notably reduced by surface etching during ligand exchange