Shunsuke Nishino

Effect of Self-Assembled Monolayer on Electroluminescence Properties of Organic Light-Emitting Diodes

We investigate the effect of a self-assembled monolayer (SAM) as a hole injection layer on the electroluminescence (EL) properties of organic light-emitting diodes (OLEDs). We modify the surface of an indium–tin-oxide (ITO) substrate using (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F-SAM) and n-decyltriethoxysilane (CH3-SAM). The current of the OLED with F-SAM is higher that those of the OLEDs with or without CH3-SAM at the same voltage and the same as that of an OLED with copper phthalocyanine (CuPc). In addition, the half-lifetime of the OLED with F-SAM is 2500 times greater than that of the OLED without the hole injection layer and about twice that of the OLED with CuPc. We discuss the conduction mechanism of the OLED in terms of the barrier height of the hole injection and the voltage distribution of the organic layers.

Chalcopyrite nanocomposite material for sustainable thermoelectrics

A chalcopyrite nanocomposite is explored as a low temperature and sustainable thermoelectric material. Chalcopyrite nanoparticles are created through a wet chemical synthetic method and display remarkable phase purity. These nanoparticle building blocks are processed into a large scale material by linking of nanoparticles by short chain ligands to enhance electrical conductivity, pressing into a pellet and subsequent thermal annealing to remove volatiles and enhance particle contacts through sintering. The resulting materials Seebeck characteristics are measured and found to be 23.6 µV/K, a P-type material.

Application of Soluble Poly(phenylenevinylene) Wrapped in Amylose to Organic Light-Emitting Diodes

Non-substituted poly(phenylenevinylene) (PPV) is an insoluble material. Ikeda et al. synthesized Amylose-PPV (APPV), which is PPV wrapped in amylose, by applying precursor route synthesis of PPV in the presence of amylase; APPV is soluble in dimethylsulfoxide. Comparison of the absorbance and the PL spectrum of APPV film with those of other organic films indicated the PL efficiency of APPV film as 0.28–0.43. The PL efficiency of PPV film is 0.27. Therefore, the amylose wrapping might improve the PL efficiency of PPV. The OLEDs emitted a green light when the OLEDs were fabricated with APPV as an emitting layer.

Modification of Ionization Potential of Poly(ethylene dioxythiophene):Poly(styrene sulfonate) Film by Acid or Base Treatment

We studied the effects of surface treatments on the surface electronic state of the poly(3,4-ethylene dioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) film. The surface treatments performed were immersion of the PEDOT:PSS film in an acid or base solution, and the exposure of the PEDOT:PSS film to acid or base vapor. The ionization potential (Ip) of the PEDOT:PSS film is modified between 4.5 and 5.3 eV by surface treatments. Ip tends to be increased by acid treatment, although it tends to be decreased by base treatment. Because Ip is modified even by brief treatments, the modification is thought to result from surface condition changes. Measurements using X-ray photoelectron spectroscopy (XPS), resistivity, and optical absorbance revealed that an electric double layer might have been formed on the surface of the PEDOT:PSS film by the treatment. The electric double layer shifts the vacuum level. Assuming the formation of an electric double layer, we can describe Ip modification by the treatment.

Chalcopyrite Nanoparticles as a Sustainable Thermoelectric Material

In this report, copper iron sulfide nanoparticles with various composition were synthesized by a thermolysis based wet chemical method. These inherently sustainable nanoparticles were then fully characterized in terms of composition, structure, and morphology, as well as for suitability as a thermoelectric material. The merits of the material preparation include a straightforward bulk material formation where particles do not require any specialized treatment, such as spark plasma sintering or thermal heating. The Seebeck coefficient of the materials reveals P-type conductivity with a maximum value of 203 µV/K. The results give insight into how to design and create a new class of sustainable nanoparticle material for thermoelectric applications.

Thermoelectric properties of high power factor sulfide NiSbS and Co substitution system Ni1− x Co x SbS

This paper describes experimental and theoretical investigations of electronic and thermoelectric (TE) properties of high power factor sulfide Ni1− x Co x SbS (x = 0, 0.10, 0.20, and 0.40). For NiSbS, even in the metallic behavior, the power factor PF of NiSbS is 1.9 mWK−2m−1 at 300 K, which exceeds the high performance TE sulfide materials as tetrahedrites or colusites. For the Ni1− x Co x SbS system, the residual electrical resistivity ρresidual increases. However, the thermopower S decreases in comparison with NiSbS. For density functional theory (DFT) calculations, the chemical potential μ for NiSbS is located at the edge of the pseudo-gap in the electronic density of states (DOS). Electronic structure μ is located at the peak of PF, as understood by the large transmission R(E) and ∂R(E)/∂E at Fermi energy E F for NiSbS. For Co-substitution, μ shifts to the valley of PF from the peak, indicating the importance of electron filling control for TE properties.