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  1. Ab initio molecular dynamics liquid-quench simulations and hybrid density functional calculations are performed to model the effects of room-temperature atomic fluctuations and photo-illumination on the structural and electronic properties of amorphous sub-stoichiometric In2O2.96. A large configurational ensemble is employed to reliably predict the distribution of localized defects as well as their response to the thermal and light activation. The results reveal that the illumination effects on the carrier concentration are greater in amorphous configurations with shorter In–O bond length and reduced polyhedral sharing as compared to the structures with a more uniform morphology. The obtained correlation between the photo-induced carrier density and the reduction in the number of fully coordinated In-atoms implies that metal oxides with a significant fraction of crystalline/amorphous interfaces would show a more pronounced response to illumination. Photo-excitation also produces In–O2–In defects that have not been previously found in sub-stoichiometric amorphous oxides; these defects are responsible for carrier instabilities due to overdoping.

     
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  2. The field-effect electron mobility of aqueous solution-processed indium gallium oxide (IGO) thin-film transistors (TFTs) is significantly enhanced by polyvinyl alcohol (PVA) addition to the precursor solution, a >70-fold increase to 7.9 cm2/Vs. To understand the origin of this remarkable phenomenon, microstructure, electronic structure, and charge transport of IGO:PVA film are investigated by a battery of experimental and theoretical techniques, including In K-edge and Ga K-edge extended X-ray absorption fine structure (EXAFS); resonant soft X-ray scattering (R-SoXS); ultraviolet photoelectron spectroscopy (UPS); Fourier transform-infrared (FT-IR) spectroscopy; time-of-flight secondary-ion mass spectrometry (ToF-SIMS); composition-/processing-dependent TFT properties; high-resolution solid-state1H,71Ga, and115In NMR spectroscopy; and discrete Fourier transform (DFT) analysis with ab initio molecular dynamics (MD) liquid-quench simulations. The71Ga{1H} rotational-echo double-resonance (REDOR) NMR and other data indicate that PVA achieves optimal H doping with a Ga···H distance of ∼3.4 Å and conversion from six- to four-coordinate Ga, which together suppress deep trap defect localization. This reduces metal-oxide polyhedral distortion, thereby increasing the electron mobility. Hydroxyl polymer doping thus offers a pathway for efficient H doping in green solvent-processed metal oxide films and the promise of high-performance, ultra-stable metal oxide semiconductor electronics with simple binary compositions.

     
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  3. Microscopic mechanisms of the formation of H defects and their role in passivation of under-coordinated atoms, short- and long-range structural transformations, and the resulting electronic properties of amorphous In–Ga–O with In : Ga = 6 : 4 are investigated using computationally-intensive ab initio molecular dynamics simulations and accurate density-functional calculations. The results reveal a stark difference between H-passivation in covalent Si-based and ionic oxide semiconductors. Specifically, it is found that hydrogen doping triggers an extended bond reconfiguration and rearrangement in the network of shared polyhedra in the disordered oxide lattice, resulting in energy gains that outweigh passivation of dangling O-p-orbitals. The H-induced structural changes in the coordination and morphology favor a more uniform charge density distribution in the conduction band, in accord with the improved carrier mobility measured in H-doped In–Ga–O [W. Huang et al. , Proc. Natl. Acad. Sci. U. S. A. , 2020, 117 , 18231]. A detailed structural analysis helps interpret the observed wide range of infrared frequencies associated with H defects and also demonstrate that the room-temperature stability of OH defects is affected by thermal fluctuations in the surrounding lattice, promoting bond migration and bond switching behavior within a short picosecond time frame. 
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