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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.

Optical and photovoltaic (PV) properties of PV cells with the structure indium tin oxide (ITO)/C60/conducting polymer (CP)/Au have been investigated. The C60/CP heterojunctions in the PV cells were fabricated by spin-coating an organic solution of CP onto the C60 underlying layer. Mixed organic solvents of chloroform and toluene were used to fabricate C60/CP interpenetrating interfaces. The C60/CP interfaces were controlled by adjusting the mixture ratio of chloroform to toluene. From the optical properties and SEM observation of C60/CP heterojunctions, it has been clarified that the interpenetrating interface of C60 and CP contributes to the balance of carrier generation and carrier transport, resulting in superior PV performance.

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.

Absorption spectra, fluorescence spectra and photoconduction characteristics in thin films of polyacetylene (PA) derivatives such as monosubstituted PAs and disubstituted PAs have been studied. In disubstituted PAs, intense fluorescence is observed with Stokes shift from the absorption edge and photocurrent is observed at around the absorption edge. On the other hand, in monosubstituted PAs, photocurrent is observed at a much shorter wavelength than the absorption edge, but photoluminescence (PL) in the film is negligible. In the solution of monosubstituted PAs, weak fluorescence is observed at a shorter wavelength than the absorption edge. These differences in fluorescence and carrier generation processes have been discussed by taking the differences of the electronic states between monosubstituted PAs and disubstituted PAs into consideration.

Organic photovoltaic cells with interpenetrating heterojunction of a conducting polymer and C60 have been fabricated by spray method. Photovoltaic cells fabricated by spray method and subsequent heat treatment have demonstrated a high photoconversion efficiency which is as the same as those fabricated by the spin coating method.

We have studied the optical and photovoltaic properties in thin films of novel types of polyacetylene derivatives such as monosubstituted polyacetylenes and disubstituted polyacetylenes. Poly(o-trimethylsilylphenylacetylene) (PPA-oSiMe 3 ) and poly(1-phenyl-2-p-n-butylphenylacetylene) (PDPA-nBu) have demonstorated their unique optical characteristics, and we found that the heterostructure photovoltaic cell of PPA-oSiMe 3 /fullerene had larger photosensitivity than that of PDPA-nBu/fullerene. The interactions between polyacetylene derivatives and fullerene at the interface have been investigated, and the photocurrent processes have been discussed by taking the electronic states into consideration.

The optical and electrical properties of novel fullerene derivatives, such as tetra(amino)fullerene epoxides (TAFEs) have been studied. The optical properties and photoconductivity in composite films and bilayer films of conducting polymers and fullerene derivatives have been also investigated. Donor-acceptor-type photovoltaic cells have been fabricated, and the photo-conversion properties have been discussed taking the photoinduced charge transfer into consideration.

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.

The field-effect mobility of a liquid-crystalline semiconducting polymer, poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (PB16TTT), has depended significantly on the surface energies of self-assembled monolayers (SAMs) formed on insulating layers. Using a SAM with fluoroalkyl groups, with a low surface energy of 13.3 mN/m, the mobility of PB16TTT reached as high as 1 cm2/V s. These results indicate that an edge-on orientation of the polymer chains progresses more favorably on the surfaces with low surface energies via the liquid-crystalline phase.

The influence of H2O and O2 on the transistor characteristics in p- and n-type organic thin-film transistors (OTFTs) fabricated on the SiO2 gate insulator was investigated. In both p- and n-type OTFTs, the threshold voltage (Vth) shifted drastically to positive direction after exposure to ambient air and dry air, although the field-effect mobilities in saturation regime were almost unchanged before and after the Vth shift. The Vth shifts to the positive direction indicate that negative charges are generated on the SiO2 gate-insulator surface by exposure to ambient air and dry air. The influence of SiO− on the gate-insulator surface and deprotonation processes of SiOH caused by H2O and O2 were discussed as the origin of the significantly positive Vth shift.

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.

We report on high crystalline thin films of liquid-crystalline polythiophene derivative, poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (PB16TTT) that exhibit terrace structures and molecular steps of its polymer chains by annealing in its liquid-crystalline phase. The crystallinity of the PB16TTT polymer films formed on SiO2 gate insulating layers with smooth self-assembled monolayer was improved by changing the octyltrichlorosilane treatment time for the SiO2, which led to reproducible high field-effect mobilities of the polymer thin-film transistors up to 0.44cm2∕Vs. High stability of the transistor for repeated stressing in ambient air was also demonstrated.

n-type organic thin-film transistors based on a thiazolothiazole derivative were fabricated on a SiO2 gate insulator treated with n-alkyl self-assembled monolayers (SAMs), which were composed of various alkyl chain lengths. The field-effect electron mobility increased depending on the alkyl chain length of the SAMs. A long alkyl chain significantly improved the on current and electron mobility. The highest electron mobility of 1.2cm2∕Vs and on/off ratio of 107 were achieved with an alkyl chain longer than that of tetradecyl-trichlorosilane. This result is attributed to the suppression of the influence of electron trap sites on the SiO2 gate insulator by employing the SAM with the long alkyl chain.

Photovoltaic cells with an interpenetrating interface between a conducting polymer layer and a fullerene layer fabricated by a solvent corrosion method have been investigated. Using a weakly dissoluble combination of a solvent and an underlayer film, we fabricated a “semilayered” structure that maintained a bilayer structure and interpenetrated at the interface of the conducting polymer and the fullerene layers. Poly(3-hexylthiophene) (PAT6) or poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) were used as the conducting polymer layer and C60 was used as the fullerene layer. In these cells, high external quantum efficiencies (EQEs) were obtained because of efficient exciton dissociations at the interpenetrating interface and efficient carrier transports by each continuous pathway between fullerene molecules of electrons and between conducting polymers of holes. An improvement was achieved by inserting a zinc oxide layer with an appropriate thickness between ITO and fullerene layer. From the comparison between the absorption spectra and the obtained EQE, the ratio of the contribution of each absorption to photocurrent was estimated. The photovoltaic properties were found to be dependent on the solvent used and corrosion time, which have been discussed by taking the form and the degree of corroded interpenetrating interface into consideration.

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.

The morphology of titanium oxide films, prepared via two different methods, oxidation following the evaporation of titanium and spin-coating a suspension of TiO2 nanoparticles, was investigated by scanning electron micrograph (SEM) and X-ray diffraction (XRD). SEM images indicated that the surface of the TiO2 film is rough and the pore size is large, compared with those of the TiO x film, which results from the connected network of the TiO2 film. Pore filling is likely to be easier in the TiO2 film than in the TiO x film due to its larger pore sizes. Poly(3-hexylthiophene) (PAT6) chains can be interrupted by the TiO2 network structure, as evidenced in UV-Vis spectrum. XRD revealed better crystallinity in the TiO2 film than in the TiO x film. The investigation of the photoluminescence (PL) spectra revealed that PL of PAT6 is quenched when it was filled into the network pores. We prepared the photovoltaic devices using PAT6 as both sensitizer and hole conductor and titanium oxide and PV films as the electron conductor, to reveal the effect of the morphology of the titanium oxide films on the photovoltaic performance. An improvement of conversion efficiency by over twofold in the TiO2 cells compared with that of the TiO x cells was observed. These phenomena suggest that the photovoltaic performances of PAT-TiO2 (or TiO x )/PV cell were dependent on the interfacial morphology between both PAT6 and TiO x and PAT6 and PV.