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We have developed low power consumption 6.18″ WQHD+ flexible AMOLED display with highly efficient top-emission type Blue OLED and successfully launched its mass production. For the next step, we develop more reliable flexible AMOLED display composed by a hole transport material with deep HOMO level and high hole injection property, and a hole-blocking material with shallow LUMO level and strong electron braking ability.

The mobility in top- and bottom-contact thin-film transistors (TFTs) based on 2,2-bianthryl (2A) was improved. The mobility of the top-contact 2A-TFT was improved from 0.25 to 1.0 cm2/Vs by octyltrichlorosilane (OTS) treatment of the SiO2 gate-insulator surface. Large grains and clear step structures corresponding to the molecular length of 2A were observed in the AFM image of a 2A film deposited on the OTS-treated SiO2. The bottom-contact 2A-TFT with typical source–drain (S–D) electrodes of Cr/Au showed a non-linear rise in the output characteristics due to the large injection barrier between the work function of Au and the HOMO level of 2A. The non-linear rise in the output characteristics was successfully improved by employing MoOx as the carrier injection layer for the S–D electrodes. Consequently, the mobility of the bottom-contact 2A-TFT with a MoOx/Au electrode was improved to 1.0 cm2/Vs, which is comparable to that in the top-contact 2A-TFT.

We investigated the air stabilities of threshold voltages ( V th ) on gate bias stress in pentacene thin-film transistors (TFTs) with a hydroxyl-free and amorphous fluoropolymer as gate insulators. The 40-nm-thick thin films of spin-coated fluoropolymer had excellent electrical insulating properties, and the pentacene TFTs exhibited negligible current hysteresis, low leakage current, a field-effect mobility of 0.45 cm 2 /Vs and an on/off current ratio of 3 × 10 7 when it was operated at −20 V in ambient air. After a gate bias stress of 10 4 s, a small V th shift below 1.1 V was obtained despite non-passivation of the pentacene layer. We have discussed that the excellent air stability of V th was attributed to the insulator surface without hydroxyl groups.

Photovoltaic cells with interpenetrating interfaces between codeposited layers of small-molecular-weight materials and conducting polymer layers fabricated by the solvent corrosion method have been investigated. In order to improve photosensitivity in the long-wavelength range of the cells, the codeposited layers of C60:metal-free phthalocyanine (H2Pc) and C60:3,4,9,10-perylene tetracarboxylic bis-benzimidazole (PTCBI) have been fabricated instead of the monodeposited layer of C60. The short-circuit current under a white light and the energy conversion efficiency of the cell using the codeposited layer have been enhanced compared to the C60 monodeposited cell because of its high sensitivity in the long-wavelength range.

Photovoltaic properties of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/C 60 /conducting polymer (CP)/Au have been investigated. The C 60 /CP heterojunction in the photovoltaic cell was fabricated by spin-coating the solution of CP onto the C 60 thin film formed on ITO. Fabricated by this process, the photovoltaic cell has demonstrated the high efficiency for solar cells based on CPs. From the optical properties of C 60 /CP heterojunction and the direct surface observation by using scanning electron microscope and atmic force microscope, it has been clarified that the interpenetrating interface of C 60 and CP contributes to the high photovoltaic performance.

Optical and photovoltaic properties of a photovoltaic cell with a structure of indium-tin-oxide(ITO)/C60/poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV)/Au have been investigated. The C60/MEH-PPV heterojunction of this cell was fabricated by spin-coating the solution of MEH-PPV onto the C60 thin film formed on ITO. Fabricated by this method, the photovoltaic cell has demonstrated a high efficiency, depending on the organic solvents used in the spin-coating process. From the optical properties and the direct observation of the C60/MEH-PPV interface, it has been clarified that such a high photovoltaic performance originates from the interpenetrating interface of MEH-PPV and C60, the morphology of which depends on the solvent used in the fabrication process of the MEH-PPV film.

Photovoltaic properties of a photovoltaic cell with structure indium–tin oxide (ITO)/ZnO/C60/poly(3-hexylthiophene) (PAT6)/Au have been investigated. The C60/PAT6 heterojunction of this cell was fabricated by spin-coating a chloroform solution of PAT6 onto the C60 thin film formed on ZnO-coated ITO. Fabricated by this method, the photovoltaic cell has demonstrated a high efficiency for solar cells based on organic polymers, i.e. a monochromic external quantum efficiency of over 70% at the peak wavelength and a power conversion efficiency of 1.0% under AM1.5 spectral illumination of 100 mW cm−2.

Polymer solar cells based on bulk heterojunction of poly(3-hexylthiophene) (PAT6) and C60 with high efficiencies have been demonstrated. The efficiencies were markedly dependent on composite ratios and annealing temperatures, and energy conversion efficiencies of 2.2% under white light and 6.5% under monochromatic light were obtained in a cell with a PAT6:C60 composite ratio of 1:0.5 annealed at 100 °C. Furthermore, the absorption of PAT6:C60 composite films in a wavelength range related to the absorption of PAT6 depended on the C60 composite ratios, and was changed significantly by annealing. These changes are discussed taking into consideration the hindrance of the crystallization of PAT6 by C60 and the phase segregation between PAT6 and C60 through the aggregation and crystallization of each molecule caused by annealing.

Photovoltaic properties of heterostructure devices of titanium oxide (TiO2) and conducting polymer thin films have been studied. Normal photovoltaic properties were stably observed upon the visible light irradiation of the wavelength range corresponding to the absorption of a conducting polymer, and unique photovoltaic properties were also observed upon the ultraviolet (UV) light irradiation of the wavelength range corresponding to the absorption of TiO2. UV light irradiation caused marked increases in the short-circuit current at the visible-wavelength range and in the open-circuit voltage. These properties have been discussed by considering the enhancement of the built-in field which originates from the hole accumulation caused by the trap levels in the TiO2 layer or TiO2∕conducting polymer interface.

Photovoltaic cells, which consist of a heterojunction of conducting polymer-fullerene systems and a zinc oxide (ZnO) thin film, have been studied. In this structure, an incident photon is used effectively because exciton generation and dissociation, which contribute to photocurrent, mainly occur on the light incident side in a conducting polymer layer. In the layered photovoltaic cells with the structure of indium-tin-oxide (ITO) / ZnO / fullerene / conducting polymer / Au, a monochromatic energy conversion efficiency of 5.2% under 0.6 mW/cm2 illumination at 500 nm and an external quantum efficiency reaching 74% at the peak wavelength have been realized, which can be explained by the interpenetrated fullerene / conducting polymer interface and the short distance between the electron-generation region and electrode enhancing electron collection to the electrode.

Optical properties and photoconduction of composite films of poly(3-hexylthiophene) (PAT-6) and metallofullerene La@C82 have been studied. The photoluminescence intensity of PAT-6 has been quenched and its photocurrent intensity has been enhanced markedly with increasing La@C82 concentration, which has been explained by the photoinduced charge transfer from PAT-6 to La@C82.

We report on the reduced contact resistance in bottom-contact (BC) pentacene thin-film transistors (TFTs) with a molybdenum oxide (MoOx) carrier injection layer. MoOx layers were placed between the gate insulator and the source-drain (S-D) electrodes instead of the conventional adhesive layer such as Cr or Ti. The performance of the BC pentacene-TFT with the MoOx injection layer was significantly improved at low operating voltages. The contact resistance of the MoOx∕Au S-D electrodes, estimated using the gated-transmission line method, was nearly two orders of magnitude smaller than that of conventional Cr∕Au electrodes at the gate voltage of −10V. The highest performance was obtained with a MoOx injection layer a few nanometers thick, which was comparable to the effective channel thickness of the pentacene-TFT on the gate insulator. This result indicated the importance of the direct connection between the MoOx injection layer and the effective channel to reduce the contact resistance.

Photovoltaic cells, with a conducting polymer/C60 interpenetrating heterostructure fabricated by spin-coating a conducting polymer onto a C60 thin film, have been investigated and demonstrated a high efficiency as solar cells based on organic materials. The photovoltaic properties of the photovoltaic cell with a structure of indium-tin oxide (ITO)/C60/poly(3-hexylthiophene)/Au have been improved by the micromodification of the ITO surface and codeposition of metal-free phthalocyanine and C60.

The optical and photovoltaic properties of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/C60/poly(3-hexylthiophene) (PAT6)/Au have been investigated. The C60/PAT6 heterojunction of this cell was fabricated by spin-coating the chloroform solution of PAT6 onto the C60 thin film formed on ITO. The photovoltaic cell fabricated by this method has demonstrated the high efficiency for a solar cell based on organic polymers. From the optical properties and the direct observation of the C60/PAT6 heterojunction, it has been clarified that the interpenetrating interface of PAT6 and C60 contributes to the high photovoltaic performance.