Hirokazu Yamane

Investigation of the electrothermo‐optical effect of a smectic LCP–nematic LC–chiral dopant ternary composite system based on SA ↔ N* phase transition

A sharp change in transmittance from a transparent state to a light scattering one within a tiny temperature range is induced accompanied with the heat-induced phase transition from a smectic-A (SA) phase to a chiral nematic (N*) one in a side-chain smectic-A liquid crystalline polymer (SALCP)–low-molecular-weight nematic liquid crystal (NLC)–chiral dopant ternary composite system with a homeotropic boundary condition. By adjusting the polymer ratio, an induced N* phase exhibiting strong light scattering over a wide temperature region has been obtained. The resulting scattering texture retained in the SA phase due to fast cooling from the N* phase can be rather stable and can be easily erased by cooling slowly from the N* phase to the SA phase after the scattering texture being heated into the N* phase again or by application of an alternating current electric field on the scattering texture directly. Based on these characteristics, it is very possible that this composite system will be used as a novel thermal addressed liquid crystal display material with respect to a fast response, a high contrast, and a durable memory effect.

Effect of p-Type Semiconductor Electrode on Photovoltaic Properties in n/p Tandem-Type Dye-Sensitized Solar Cell

To improve the light-to-electric energy conversion efficiency of a dye-sensitized solar cell, a p-type semiconductor electrode was introduced to the cell so that n/p tandem-type solar cell was composed. In the tandem cell, the TiO2 adsorbed with N719 dye molecules and the p-type semiconductor were used an anode and a cathode, respectively, and acetonitrile solution containing iodide was done as an electrolyte. The cathode was prepared on a surface of platinum layer formed on a FTO glass plate by plasma spattering CuxBiyOz as the p-type semiconductor. Short-circuit current density and conversion efficiency of the tandem cell were larger than those in a cathode without the p-type semiconductor layer. The p-type semiconductor layer will be able to absorb low energy photons passed through the anode. After ZnO particles were coated on a surface of the p-type semiconductor layer, open-circuit voltage was increased. Such coating of the particles will be effective to depress a back-transfer at the interface between the p-type semiconductor layer and the electrolyte and band-bending of the p-type semiconductor.

Thermo-recording in (side chain type smectic A liquid crystal polymer/nematic liquid crystal/chiral dopant/dichroic dye) composite with a low power laser

Thermo-recording in a [side chain type smectic A liquid crystal polymer (SmA-LCP)/nematic liquid crystal (N-LC)/chiral dopant/dichroic dye] composite has been realized by using 2mW of power from a He-Ne laser. The laser irradiation-induced phase transitions of smectic A (SmA) → chiral nematic (N*) → SmA formed the dominant thermo-recording mechanism in the composite. Thermo-recording in the (SmA-LCP/N-LC/chiral dopant/dichroic dye) composite exhibited a higher contrast when compared with the non-polymeric (SmA-LC)/N-LC/chiral dopant/dichroic dye composite.

Effects of Composition on Thermo-Optical Properties of (Side Chain Smectic-A Liquid Crystalline Polymer/Low Molecular Weight Nematic Liquid Crystal/Chiral Dopant) Ternary Composite System

Abstract A drastic change from a transparent smectic-A (SmA) phase to a light-scattering chiral nematic (N*) one is achieved in [side chain smectic-A liquid crystalline polymer (SCSmALCP)/low molecular weight nematic liquid crystal (LMWNLC/chiral dopant] a ternary composite system with a homeotropic boundary condition. The light-scattering state of the induced N* phase can be resumed into the initially transparent SmA phase on cooling slowly, and be frozen in the SmA phase on cooling rapidly. The effects of the composition of the ternary composite system on such thermo-optical characteristics are investigated.

High-speed memory switching of liquid crystalline copolymer/low molecular weight liquid crystal composite systems

Reversible and bistable electro-optical switching characteristics have been investigated for induced smectic composite systems composed of side chain type nematic liquid crystalline polymer (nematic LCP) or its copolymer with weak polar methoxy terminal groups in the side chains and low molecular weight nematic liquid crystals (nematic LCs) with strong polar cyano end group. The liquid crystalline copolymer (LCcoP) with weak polar methoxy terminal groups in the side chains was used in order to improve the response speed of the bistable and reversible light switching for the binary composite system at room temperature. Although the LCcoP with 52.5 mol% substituted mesogenic side chains did not exhibit any mesophase characteristics at any temperature, this LCcoP induced a smectic state by mixing nematic LCs. A reversible and bistable electro-optical switching with a short response time (approximately 100 ms) was realized for the induced smectic binary composite system upon application of an appropriate electric field at room temperature.

Effect of Polymeric p-Type Semiconductor on Photovoltaic Properties in Dye-Sensitized Solar Cell

A hole formed in photo-excited dye molecule under illumination is transferred to cathode with iodine ion in electrolyte solution in the dye-sensitized solar cell developed by M. Grätzel and the conductivity of the iodine ion affects conversion efficiency of the cell. In this work, effect of the polymeric p-type semiconductor on the hole transferability is investigated. PEDOT:PSS and P3HT were used as the p-type semiconductors. Dye-sensitized solar cells were composed of aluminium plate, Nb-doped TiO2 layer adsorbed with TCNQ, the electrolyte solution containing iodine ions, and ITO glass plate. In a solid-type cell substituted the electrolyte solution with the p-type semiconductor, photocurrent was not generated. The photocurrent was generated in the solar cell by introducing the electrolyte solution containing iodine ions between the ITO glass and the p-type semiconductor formed on the dye-adsorbed Nb-doped-TiO2 layer or between the dye-adsorbed Nb-doped-TiO2 layer and the p-type semiconductor formed on the ITO glass. The conversion efficiency increased with the introduction of the p-type semiconductor such as PEDOT:PSS, compared only with the electrolyte solution. The p-type semiconductor containing iodine ions promote the hole transfer of iodine ion, compared with that in the electrolyte solution.

Preparation of Organic Photovoltaics Using the Sensitizing Effect of Quantum Dots

Organic photovoltaic is one of the solar cell consists of fullerene derivative which is an n-type semiconductor and the conductive polymer as p-type semiconductor. In my research, silicon quantum dots was introduced to the active layer consisting of fullerene derivative (PCBM) and a conductive polymer (PCPDTBT), to prepare the hybrid photovoltaic. The prepared hybrid solar cell with Si quantum dots achieved better cell performance compared with controlled solar cell without quantum dots. The hybrid solar cell showed larger value of Incident photon-to-current conversion efficiencies and lower photoluminescence intensity. This indicated that domain size among phase separation in active layer was made smaller than the active layer of controlled solar cell, by introducing Si quantum dots. This change of aggregation structure by quantum dots was contributed to the improvement of cell characteristics.

Bistable Memory Switching of (Liquid Crystalline Copolymer/ Low Molecular Weight Liquid Crystal) Composite Systems

Abstract Bistable electro-optical switching characteristics have been investigated for composite systems in a smectic phase induced by mixing a side chain type nematic liquid crystalline polymer (nematic LCP) or its copolymer with weak polar methoxy terminal groups in the side chains and low molecular weight nematic liquid crystals (nematic LCs) with strong polar cyano end groups. The liquid crystalline copolymer (LCcoP) with weak polar methoxy terminal groups in the side chains attaching to a polysiloxane main chain was used in order to improve the response speed of the bistable light switching for the binary composite system. Although the LCcoP with 52.5 mol% substituted mesogenic side chains did not exhibit any mesophase characteristics at any temperature, this LCcoP induced a smectic state by mixing nematic LCs. A reversible and bistable electro-optical switching with a short response time (∽100 ms) was realized for the induced smectic binary composite system upon the application of an appropriate electric field at room temperature.

Fast Bistable Switching Composite Systems of Side-chain Liquid-crystalline Copolymer and Low Molecular Weight Liquid Crystals

Abstract Mesomorphic characteristics and bistable light switching properties of the composite system composed of various side chain type liquid crystalline copolymers (LCcoPs) which includes the flexible dimethylsiloxane segment as one constituent of the copolymer and low molecular weight nematic liquid crystals (nematic LCs) have been investigated in order to construct the optimum smectic binary composite system with both fast light switching characteristics and stable memory effects at room temperature. Two types of novel (LCcoP/nematic LCs) composite systems in a smectic phase studied were (1) (pseudo LCcoP with weak polar methoxy terminal groups/nematic LCs with strong polar cyano terminal groups) and (2) (smectic LCcoP with strong polar cyano terminal groups/nematic LCs with the same terminal groups). The response speed of bistable light switching for the binary composite system could be remarkably improved by reducing the LCcoP fraction maintaining a smectic state at room temperature due to an incre...

Spacer length dependence of mesomorphic characteristics and bistable electro-optical effects for smectic (liquid crystalline copolymer/liquid crystals) composite systems

Abstract Mesomorphic characteristics and bistable electro-optical switching effects of smectic composite systems composed of side chain liquid crystalline copolymer (LCcoP) with a weak polar methoxy terminal group in a side chain and low molecular weight nematic liquid crystals (nematic LCs) with each strong polar cyano end group have been investigated. The spacer length of the mesogenic side chain in LCcoP has strongly affected the mesomorphic characteristics and the electro-optical effects of the (LCcoP/LCs) composite systems. The response speed of the binary composite systems became faster with a decrease of the spacer length. The binary composite systems showed reversible and bistable electro-optical switching characteristics with response time of ∼100 ms, that is, a light scattering state and a transparent one upon the application of ac electric fields with low frequency (up to - Hz) and high one (10–105 Hz), respectively. However, a light scattering state was also observed due to the sign reversal o...