Newly Observed Temperature and Surface Ligand Dependence of Electron Mobility in Indium Oxide Nanocrystals Solids

Abstract

We developed a new class of organic surface ligands; 2-aminopyridine (2AP), 4-aminobenzoic acid (4ABA), and benzoic acid (BA); for use in the solution ligand exchange of nanocrystals (NCs) in the presence of nitric acid (HNO3). Here, colloidal NCs synthesis is used for the first time. These short, air-stable, easy-to-model ligands bind to the surface of the indium oxide nanocrystal (In2O3 NC) and provide the electrostatic stabilization of NC semiconductor dispersions in N,N-dimethylformamide, allowing for a solution-based deposition of NCs into thin-film transitors (TFTs). The shorter organic ligands greatly facilitate electronic coupling between the NCs. For example, thin films made from 2AP-capped In2O3 NCs exhibited a high electron mobility of μ≈9.5 cm2/(V·s), an on-off current ratio of about >10(7), and a subthreshold swing of 2.34 V/decade. As the ligand length decreased, the electron mobility increased exponentially. Furthermore, we also report on the temperature-dependent behavior of the electron transport of In2O3 NCs films, in the case in which thin films were cured at 150 °C, as the 2AP, BA, and 4ABA ligand molecules were sustained on the NC. We demonstrated a hopping transport mechanism instead of a band-like transport, and the thermally activated carrier transport process governed the charge transport in our In2O3 NC thin-film solid.

Bilayer PbS Quantum Dots for High‐Performance Photodetectors

“…Also, the electronic properties of PbS QDs can be easily modified by surface ligand chemistry . For example, efficient charge transport between QDs and high carrier mobility can be achieved by replacing the long insulating aliphatic ligands with short ones to enhance electronic coupling between QDs . Furthermore, the ligand treatment can also tune the energy levels of PbS QDs by forming different dipole moments at the QD–ligand interface .…”

Solution‐processed Tetrafluoroborate‐capped In2O3 Nanocrystal Thin‐Film Transistors

“…where μ is the mobility, μ 00 is the temperature independent pre‐exponential factor, T is the temperature, E a is the activation energy, and k B is the Boltzmann constant Furthermore, E a can be derived from the slope of Arrhenius plot and is 32, 31, and 25 meV for In 2 O 3 ‐BF 4 − NCs thin film annealed at 150, 250, and 350 °C, respectively. The E a decreases with increasing annealing temperature, because of smaller barrier between the nearest neighbor NCs in In 2 O 3 ‐BF 4 − NCs thin film with increasing annealing temperature …”

“…At a low annealing temperature of 350 C, In 2 O 3 -BF 4 − thin film exhibited a mobility of 13.0 cm 2 /V/s, which is higher than previously reported for In 2 O 3 NC TFT. 21,28 To deeply understand In 2 O 3 -BF 4 − thin film, mechanism of electron transport on In 2 O 3 -BF 4 − NCs thin films was investigated by measuring the TFT properties at different temperatures from 223 to 323 K in a vacuum chamber.…”

“…The E a decreases with increasing annealing temperature, because of smaller barrier between the nearest neighbor NCs in In 2 O 3 -BF 4 − NCs thin film with increasing annealing temperature. 21…”

“…19 Previously, we investigated two types of surface engineering-utilization of shorter organic ligands or inorganic ligands for the semiconducting oxide nanocrystal to increase the mobility of In 2 O 3 NC TFT devices. Replacing long chain oleic acid (OA) ligand of the In 2 O 3 NC by short ligand such as β-alanine, benzoic acid, 4-aminobenzoic acid, and 2-aminopyridine has been investigated to decrease the interdistance [20][21][22] ; however, these NC TFTs exhibited low mobility under the NCs thin film annealing conditions in the low temperature range 150-350 C. As for the 350 C annealing condition, oleic acid, β-alanine, benzoic acid, 4-aminobenzoic acid, and 2-aminopyridine ligands, in their In 2 O 3 NC TFT devices, showed the mobilities of 0.4, 2.2, 3.1, 2.6, and 9.5 cm 2 /V/s, respectively. [20][21][22] This is because a part of organic ligands still survived on the NC surfaces, obstructing the charge transport through NC solids, owing to the high decomposition temperature of those organic capping ligands.…”