For a material for organic thin-film transistors, not only high mobility but also low threshold voltage and long-term stability are important requirements. In order to realize these properties, materials with relatively large oxidation potentials, namely weak donors, have been designed as p-channel organic semiconductors. Here we propose a different strategy; transistor properties of dibenzotetrathiafulvalene (DBTTF) are significantly improved by the introduction of tert-butyl groups. Although this chemical modification does not much change the ionization potential, small threshold voltage and stability over several months are attained together with the improved mobility, probably due to some kind of passivation effect of the bulky tert-butyl groups. In contrast, the systematic fluorine substitution rapidly diminishes the transistor performance. There are two kinds of herringbone structures with much different dihedral angles of about 50° and 130°, and the tert-butyl compound falls into the former category.

Quantum dots (QDs) are expected to be applied to emitting materials used in wide-color-gamut displays. However, the development of low-toxic alternatives is necessary because QDs that exhibit high color purity and highly efficient emission contain toxic materials such as Cd. In the present study, quantum dot light-emitting diodes (QD-LEDs) prepared using ZnInP/ZnSe/ZnS QDs as InP-based QDs were fabricated, and their electroluminescence (EL) properties were investigated. The synthesized QD dispersion showed a green photoluminescence (PL) spectrum with a peak wavelength of 509 nm, a full-width at half-maximum (FWHM) of 41 nm, and a PL quantum yield of 59.8%. Tris[2,4,6-trimethyl-3-(pyridin-3-yl)phenyl]borane (3TPYMB), which is an electron-transporting material (ETM), was added to the emitting layer (EML) of the QD-LEDs. The QDs and the ETM were nonuniformly deposited, the density of QDs in the EML was reduced, and the process of injecting electrons and holes into the QDs was changed. 3TPYMB assisted in recombination in the QDs because the electron injection barrier from 3TPYMB to the QDs was sufficiently small and because the deep highest occupied molecular orbital level effectively blocked holes. As a result, the external quantum efficiency was improved from 0.24% to 1.01%, and stable EL spectra with a peak wavelength of 522 nm and an FWHM of 46 nm, similar to the PL spectrum of the QD film, were obtained without being dependent on luminance. A bright and stable green EL emission was achieved with an InP-based QD-LED blended with 3TPYMB.

Group III-nitride nanocrystals are promising candidates for lighting applications. However, development of their colloidal quantum dots (QDs) has not progressed because of issues with the synthesis of indium nitride (InN) nanoparticles, such as the long reaction time and the generation of indium metal as a by-product. Here, we propose a new synthetic method that can solve almost all of the above problems and improve the quality of InN nanocrystals. In addition, we demonstrate that Ga-In-N QDs and Zn-In-N QDs synthesized using the proposed method exhibit photoluminescence.

No abstract