Doping Indium Oxide Films with Amino-Polymers of Varying Nitrogen Content Markedly Affects Charge Transport and Mechanical Flexibility

Here, correlations between polymer structure and charge transport in solution-processed indium oxide, In₂O₃:polymer blend flexible thin film transistors (TFTs) are investigated using four polymers having electron-donating amine functionalities (polyethyleneimine (PEI), poly(allylamine), polyethyleneimine ethoxylated (PEIE), and PVP-NH₂ (PVP; poly(4-vinylphenol)), and two PEI-PEIE mixtures) with varied atomic amine nitrogen content (N%) of 12.6, 9.1, 6.9, 2.6, respectively. These amino-polymers influence the semiconducting oxide film TFT electron mobilities via a delicate interplay of electron transfer/doping, charge generation/trap-filling, film morphological/microstructural variations, which depend on the polymer structure, thermal stability, and N%, as well as the polymer content of the In₂O₃ precursor and the carbon residue content in In₂O₃. Thus, increasing the N% from 0.0% in the control PVP to 12.6% in PEI increases the electron doping capacity, the polymer content of the blend formulation, and the blend TFT field-effect mobility. Optimal polymer incorporation invariably enhances charge transport by as much as ≈2×, leading to a maximum carrier mobility of 8.47 ± 0.73 cm² V⁻¹ s⁻¹ on rigid Si/SiO_x substrates and a remarkable 31.24 ± 0.41 cm² V⁻¹ s⁻¹ on mechanically flexible polyimide/Au/F:AlO_x substrates with Al contacts. Furthermore, all of the polymers equally enhance the mechanical durability of the corresponding In₂O₃:polymer blend TFTs with respect to mechanical stress.